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Ahn, Sung Won Oscillation of quenched slowdown asymptotics of random walks in random environment in Z. Akiyama, Reiko Language, culture, and identity negotiation: perspectives of adolescent Japanese sojourner students in the Midwest, USA. Akkala, Arun Goud Asymmetric underlap optimization of subnm finfets for realizing energy-efficient logic and robust memories. AlJaberi, Hana Designing prenatal m-Health interventions through transmigrants reflection on their pregnancy ecology.
Allen, Benjamin The impact of the foot and mouth disease control pathway on milk production in India. Allen, Jennifer L Macronutrient-flavonoid interactions, effects in model food matrices. Allen, Wai K Miocene-Pliocene strike-slip basin development along the Denali fault system in the eastern Alaska range: Chronostratigraphy and provenance of the Mccallum formation and implications for displacement.
Almeida, Leah Zoe Effects of Lake Erie hypoxia on fish habitat quality and yellow perch behavior and physiology. Al Noman, Abdullah Optical characterization of on-chip silicon nitride microresonators. Alotaibi, Ahmed Mohammed Development of a mechatronics instrument assisted soft tissue mobilization IASTM device to quantify force and orientation angles.
Altarabsheh, Ahmad Ghazi Managing urban wastewater system using complex adaptive system approach. Amankwah, Akuffo Subsidies, aquaculture technology adoption, and welfare impacts in Ghana and Kenya. Anderson, Nickolas H Controlling electronics for the formation of high valent uranium imido complexes. Arora, Nigam Bir Utilization of ferrioxamine microarrays for the rapid detection of pathogenic bacteria.
Aslam, Kiran Deciphering the role of Hsp31 as a multitasking chaperone. Assisi, Clara Genomic and transcriptomic analysis of biofilm formation in persistent and transient L. Ayres, Drew C A collaborative integrated stem teaching: Examination of a science and math teacher collaboration on an integrated stem unit. Azarmi, Mehdi End-to-end security in service-oriented architecture. Azzato, Ariana Experimental evaluation of an iPad-based augmentative and alternative communication program for early elementary children with severe, non-verbal autism.
Backing, Thomas H Regularity of solutions and the free boundary for a class of Bernoulli-type parabolic free boundary problems with variable coefficients. Bae, Yeon Jin Integrated design tool of building system optimization for building life cycle cost. Balasubramanian, Shambhavi Fuel type estimation using fuel system parameters. Banks, Devin E Examining differential relationships of substance use and risky sexual behavior among African American and White adolescents. Baradwaj, Aditya G Solid state charge transport in radical polymers. Barrett, Daniel P Learning in vision and robotics.
Barthur, Ashrith Computational environment for modeling and analysing network traffic behaviour using the divide and recombine framework. Baskaran, Savitha Visualization of spatio-temporal data in two dimensional space. Batra, Jennifer C Innovation as everyday action: A case study of organizational discourse and the local meaning of innovation. Batty, Leslie Danel Of angels and animals: Sexuality, spirituality, and social contexts in Rebecca West's modernist novels.
Batz, Cassondra L A meta-analytic examination of the role of gender inequality in explaining gender differences in subjective well-being. Beaty, Melissa S Functional characterization of the Rvc protein of Mycobacterium tuberculosis. Belal, Hatem Mohamed Modifying burning rate and agglomeration size in aluminized composite solid propellants using mechanically activated metals. Bell, Colin D Influence of stormwater control measures on watershed hydrology and biogeochemical cycling.
Bell, Darren Thomas Size scaling of strength and toughness for 3D printed polymer specimens. Bemis, Kyle A framework for the statistical analysis of mass spectrometry imaging experiments. Benham, Sara J Deficits in sound pattern sequencing in children with specific language impairment: A networks approach. Benskin, Joanna Perceval's sister and Juliet Capulet as disruptive guides in spiritual quests. Bercich, Rebecca A Improving the mechanistic study of neuromuscular diseases through the development of a fully wireless and implantable recording device.
Berdanier, Catherine G. P Learning the language of academic engineering: Sociocognitive writing in graduate students. Bergman, Megan N Using academic and learning analytics to explore student success in an online graduate program in communication. Berman, Alycia G Influence of mechanical stimulation on the quantity and quality of bone during modeling. Besser, Erin D Exploring the role of feedback and its impact within a Digital Badge system from multiple perspectives: A case study of preservice teachers. Bhamra, Hansraj Singh Micro-power circuits and systems for wireless sensor nodes and implantable medical devices.
Bhargav, Amruth Development of novel cathodes for high energy density lithium batteries. Bhuiyan, Mansurul MD. Biggs, Bruce A Examining law enforcement officer job satisfaction and burnout through the lens of empowerment theory. Binarandi, Ghazi Artificial neural networks for wireless structural control. Bland, James R Three essays in economics.
Blood, Bridget Lorraine Behavioral responses of Pityophthorus juglandis to volatiles of walnut and Geosmithia morbida, the causal agent of thousand cankers disease. Bodicherla, Dhiraj Zephyr: A social psychology-based mobile application for long-distance romantic partners. Boo, Jeongjoon Enhancing a flight dispatcher display for safer flight operations. Book, Todd A Structural integrity of additive materials: Microstructure, fatigue behavior, and surface processing. Booth, Joran W How pre-ideation methods and skills affect and remove barriers to ideation. Bosanac, Natasha Leveraging natural dynamical structures to explore multi-body systems.
Boussios, David A Modeling of a cereal-livestock production system in Karak, Jordan: A dynamic stochastic programming approach. Bowen, Gregory A Sounding sacred: The adoption of biblical archaisms in the Book of Mormon and other 19th century texts. Boylan, Daniel H The innovative use of Twitter technology by bank leadership to enhance shareholder value. Bragg, John Campbell Silk fibroin-reinforced hydrogels for growth factor delivery and in vitro cell culture. Brar, Jagpinder S Modeling for thermal resistance of non-O shiga toxin producing Escherichia coli in ground beef.
Brayfield, Russell Scott Optical emission spectroscopy of high voltage cold atmospheric plasma generated using dielectric barrier discharges. Brice, William Disability visibility and stigma threat: Effects on the performance, stress, and self-control of disabled workers. Brindley, Jacob A Essays in experimental economics on contract design. Brock, Amanda M Evaluating the impact of a wood-chip bioreactor on phosphorus concentrations. Bronikowski, Scott Alan Grounding robot motion in natural language and visual perception.
Brown, Anne V Understanding the molecular regulation of senescence in Glycine max. Browning, Tyler A Direct photon anisotropy and the time evolution of the quark-gluon plasma. Builta, Stephen Assessing fuel burn inefficiencies in oceanic airspace. Bunka, Christopher A Globalization and state: Factors contributing to the contemporary food security crisis.
Bunnell, Wayne A Multimedia techniques for construction education and training. Busquets, Enrique Advanced control algorithms for compact and highly efficient displacement-controlled multi-actuator and hydraulic hybrid systems. Busse, Margaret M Characterization of a continuous-flow reactor for solar UV water disinfection. Byrd, Elizabeth S A unique perspective on the demand for livestock product attributes. Cabral do Nascimento, Vinicius Magnetic equivalent circuit based permanent magnet characterization.
Cahill, Katie Anne Democracy is not enough: Accountability, international organizations, and the politics social good distribution. Calic, Goran Creativity in organizations: Antecedents and outcomes of individual creativity. Campbell, Emily Does mentoring buffer women in science from the effects of perceived discrimination on career outcomes?
Cao, Lei Dislocations in the nanoscale: A phase-field view. Cao, Muning A study of how Chinese ink painting features can be applied to 3D scenes and models in real-time rendering. Cao, Yudong Combinatorial algorithms for perturbation theory and application on quantum computing. Carichino, Lucia Multiscale mathematical modeling of ocular blood flow and oxygenation and their relevance to glaucoma. Carnes, Mark T Conceptual understanding of threshold concepts of electrical phenomena: Mental models of senior undergraduates in electrical engineering.
Carriere, Danielle E Resilience, suicide, and enrollment in higher education: Three essays on impacts of recession. Carter, Carlos D Antibacterial activity of essential oil encapsulated sodium iota-carrageenan fibers. Cassani, Simone Blood circulation and aqueous humor flow in the eye: Multi-scale modeling and clinical applications. Casteloes, Karen S Techniques and technologies for decontaminating chemically contaminated premise plumbing infrastructure. Castillo, Marcelo J Essays in international migration.
Cavett, Lee A Using security risk analysis: Is the bring your own device policy becoming a liability risk within healthcare? Cedeno Agamez, Miguel Aging effects in automated face recognition. Cen, Lei A study of security issues of mobile apps in the android platform using machine learning approaches. Cervantes Botero, Victor Hernando An application of contextuality-by-default in a psychophysical double detection experiment.
Chae, Junghoon Visual analytics of location-based social networks for decision support. Chakrabarty, Ankush Supervised learning-based explicit nonlinear model predictive control and unknown input estimation in biomedical systems. Chamberlain, Kyle Purification and preparation of intrinsically disordered proteins for NMR spectroscopy. Chandler, Myles G Identifying predictors of university sales competition performace: A social-cognitive account.
Chandrasegaran, Ramaswamy Senthil Kumaran Tools and methods to analyze multimodal data in collaborative design ideation. Chandrasekar, Rohith Development of coherent light sources at the nanoscale using optical metamaterials. Chan, Kai-Chi On the 3D point cloud for human-pose estimation. Chan, Kevin J The effects of scarring on face recognition. Chatzidakis, Stylianos Cosmic ray muons for spent nuclear fuel monitoring.
Chen, Binghe Least-squares finite element method for singularly perturbed problems and the Oseen problem. Chen, Chun-Liang Functional and structural characterization of the mevalonate diphosphate decarboxylase and the isopentenyl diphosphate isomerase from Enterococcus faecalis. Chen, Ji Investigating and expanding the functionality of RNA catalysts: Studies of the hepatitis delta virus, the hammerhead, and the aminoacyl-tRNA synthetase-like ribozymes.
Chen, Keru Physiological aspects of relative changes in nitrogen and plant density stress tolerances over a year period of US maize hybrid introductions. Chen, Long Improvement of treatment for prostate cancer and involvement of Plk1. Chen, Peng-Chu Systemic risk in financial networks. Chen, Xi Impact of dietary modification on aflatoxicosis in poultry. Chen, Yafang Structural and functional studies of the papain-like protease 2 from mouse hepatitis virus. Chen, Yi Local polynomial chaos expansion method for high dimensional stochastic differential equations.
Chen, Yi-hui Effects of age of learning, family, and social environment on attitude and proficiency in EFL among Taiwanese adults. Chernouski, Libby C Rethinking reference: Towards a holistic approach to linguistic reference. Chisama, Benjamin Franklin Farmers' use of mobile phone technology for agricultural information services in Lilongwe District, Malawi. Chiu, Charles Yicheng The effects of chloride-based deicing chemicals on degradation of portland cement mortars with alkali reactive aggregate. Choi, Meena A flexible and versatile framework for statistical design and analysis of quantitative mass spectrometry-based proteomic experiments.
Choi, Mun S Pilot study of the effect of high-protein, renal-appropriate meals during hemodialysis on intradialytic hypotension in maintenance hemodialysis patients. Chojnacki, John T Dynamic triaxial compression experiments on borosilicate and soda-lime glass. Cho, Younghyun Development and evaluation of a watershed-scale hybrid hydrologic model. Chu, Jou-Mei Mechanical properties of transgenic silkworm silk at high rate impact. Chulis, Kimberly Data mining Twitter for cancer, diabetes, and asthma insights. Clark, Christopher Lewis The investigation of carbon-fluorine bond activation by uranium and evaluation of a tris-oxazoline based tripodal ligand to support low-valent uranium centers.
Clinkenbeard, Paige E Teen suicide and other destructive behaviors in contemporary young adult literature: The subjects, the literature, and what it means for educators. Coley, Scott M On the consequences of skeptical theism. Collins, Scott J The impact of global environmental changes on an exotic invasive species, Slliaria petiolata garlic mustard. Conrad, Alicia E Effects of exposure to agricultural drainage ditch water on survivorship, distribution and abundance of riffle beetles Coleoptera: Elmidae in headwater streams of the Cedar Creek Watershed, Indiana.
Cook, Amanda C Essays on health insurance. Cook, Timothy Daniel Expanding M cyclam chemistry; cobalt acetylide complexes for charge delocalization, and functionalized nickel complexes for CO2 reduction. Corkran, Sydney Cooper Comparison of processing parameters in large and small scale beef processing plants and their impact on Escherichia coli prevalence.
Corsten, Anthony Nicholas Evaluation of several pre-clinical tools for identifying characteristics associated with limb bone fracture in thoroughbred racehorses. Coskun, Esra Language and attribution: Women and identity. Coulthard, Glen J A descriptive case study: Investigating the implementation of web based, automated grading and tutorial software in a freshman computer literacy course.
Cox, Perry L Lightcraft Previzion in distance education. Crespo, Jonah Greenfield Asset allocation in frequency and in 3 spatial dimensions for electronic warfare application. Croft, Marcia M The role of African leafy vegetables in food security. Cruz, Lauren M The effects of light intensity and wavelength on in-water orientation of olive ridley sea turtle hatchlings Lepidochelys olivacea.
Cui, Hongming A case study of barriers to Lean Six Sigma adoption in China's manufacturing industry, from entrepreneurial view point. Cui, Wei Design and application of peptide-based fluorescent biosensors for protein tyrosine kinases. Cui, Yan Interval analysis techniques for field mapping and geolocation. Cui, Yi Studies of rechargeable lithium-sulfur batteries. Daly, Christine Ann Seeking certainty: Are people who are experiencing relational doubt more sensitive to relationship cues? Dangeti, Sanmathi Tangible interaction as an aid for object navigation in 3D modeling.
Dang, Zhuoran Experimental study of two phase upward flow in vertical one-inch pipe. D'Aquila, Theresa M Intestinal cytoplasmic lipid droplets, associated proteins, and the regulation of dietary fat absorption. Darko, Francis Addeah Essays on Malawian agriculture: Micro-level welfare impacts of agricultural productivity; profitability of fertilizer use; and targeting of fertilizer subsidy programs. Datta, Dhrubajyoti Micromechanical fracture model for ductile-brittle bimaterial interfaces. Davis, Beshaun Jamaal Making meaning in the presence of sub-threshold psychotic symptoms: An investigation of metacognitive capacity in psychometric schizotypy.
Davis, John Michael The development and evaluation of a lean six sigma advanced manufacturing methodologies course for aeronautical engineering technology curriculum. Davis, Nathan J Mechanical dispersion of semi-solid binders in high-shear granulation. Davis, Zachary G Essays on university competition. Deatherage, Scott S Facebook engagement on college students' interpersonal and intrapersonal functioning.
Degenstein, John C Fast-pyrolysis of biomass related model compounds: A novel approach to experimental study and modeling. DeKorver, Brittland K Undergraduate students' goals for chemistry laboratory coursework. Deldar, Majid Decentralized multivariable modeling and control of wind turbine with hydrostatic drive-train.
DeNardo, Nicholas M Additive manufacturing of carbon fiber-reinforced thermoplastic composites. Deng, Yexin Two-dimensional electronics and optoelectronics: From materials syntheses to device applications. Dennis, Tana Shea Influence of dietary component manipulation and feed management strategies on growth and rumen development of weaned dairy heifers. Deuser, August Robert Technology, nostalgia, and coming-of-age in Salinger's short fiction. DeVilbiss, Frank T Is metabolism goal-directed? Investigating the validity of modeling biological systems with cybernetic control via omic data.
Dey, Sayan Role of river bathymetry in hydraulic modeling of river channels. Dhamankar, Nitin S An immersed boundary method for efficient computational studies of nozzles designed to reduce jet noise. Dhillon, Jaapna The effects of including almonds in an energy-restricted diet on weight, body composition, visceral adipose tissue, blood pressure and cognitive function. Diao, Kelu Hardware accelerated redundancy elimination in network system.
Ding, Zi'ang Lagrangian analysis of vector and tensor fields: Algorithmic foundations and applications in medical imaging and computational fluid dynamics. Doh, Iyll-Joon Development of bacterial colony phenotyping instrument using reflected scatter light. Douilly, Roby 3D dynamic rupture simulation and local tomography studies following the Haiti earthquake. Dow, Ximeng You Nonlinear optical methods for the analysis of protein nanocrystals and biological tissues.
Duarte Gomez, Eileen Enid The use of lux enzymes to investigate the association between irreversible protein denaturation and pressure-mediated inactivation of Escherichia coli. Dubikovsky, Sergey I The association between tolerance for ambiguity and fear of negative evaluation: A study of engineering technology capstone courses. Duffy, Alexandra G Billbug Sphenophorus spp.
Du, Juan Complex formation by alpha-lactalbumin and polysaccharide copolymers. Du, Mike Realtime dynamic binary instrumentation. Dundar, Aysegul Learning from minimally labeled data with accelerated convolutional neural networks. Dunn, Jonathan M Nanoscale phonon thermal conductivity via molecular dynamics. Durkes, Abigail Cox The effects of acidified pepsin on porcine vocal fold tissue: Developing a porcine model of laryngopharyngeal reflux disease. Eadara, Archana Modeling, analysis, and simulation of Muzima fingerprint module based on ordinary and time Petri nets.
Easton, Mckay Whetton Density functional theory calculations complement mass spectrometry experiments in the investigation of biomass fast pyrolysis and ion-molecule reaction mechanisms. Eberline, Andrew Dale Perceptions of and experiences with the Indiana teacher evaluation system in physical education.
Edalatnoor, Arash Energy optimization of air handling unit using CO2 data and coil performance. Edelman, Joshua B Secondary instabilities of hypersonic stationary crossflow waves. Edelman, Peter J Interplanetary mission design with applications to guidance and optimal control of aero-assisted trajectories. Ehlers, Shawn Gregory Rearward visibility issues related to agricultural machinery: Contributing factors, potential solutions.
Engerer, Jeffrey D Rapid transient cooling utilizing flash boiling and desorption on graphitic foams. Erdei, Ronald An examination of the employment of the pair programming methodology as a collaborative instructional scaffold on college student procedural learning and programming self-beliefs. Escalante, Lucio Navarro Discovery and functional analyses of Hessian fly effector-encoding genes. Eun, Joonyup Models and optimization for elective surgery scheduling under uncertainty considering patient health condition. Ewetz, Rickard F Synthesis of clock trees with useful skew based on sparse-graph algorithms.
Faheem Ibeacon based proximity and indoor localization system. Fahmi, Tazin Stress and immunological evaluations of sea urchin treated with four different nutraceuticals. Falk, Courtney Knowledge modeling of phishing emails. Fang, Maureen M Integrating precision machining process capability data into product feature design process. Fan, Jingxian Taming tail latency for erasure-coded, distributed storage systems. Fan, Xiaozhe An LED-based image sensor with energy harvesting and projection capabilities college of technology.
Feng, Chao Biophysical studies of the allosteric regulatory mechanism of Syk tandem SH2 domains interacting with immunoreceptor tyrosine-based activation motifs. Feng, Qingyu Hydrologic and water quality impacts from perennial crop production on marginal lands. Ferialdy, Arfinandi Graph theoretical analysis of the Dynamic Lines of Collaboration model for disruption response.
Fezi, Kyle S Modeling transport phenomena and uncertainty quantification in solidification processes. Frappier, Ann M An investigation of composite failure analyses and damage evolution in finite element models. Fu, Jiahong Uncertainty quantification on industrial high pressure die casting process. Fu, Rong Early parental loss, socioeconomic stressors, and health in later life: Evidence for gender disparity.
Gabet, Ryan M A comparative forensic analysis of privacy enhanced web browsers. Gaeta, Christopher M Quit playing with your watch: Perceptions of smartwatch use. Gaffar, Md Explicit and unconditionally stable finite difference time domain methods for general electromagnetic analysis. Gaitonde, Aalok Jaisheela Uday Thermal transport in lithium ion batteries: An experimental investigation of interfaces and granular materials. Gall, Aaron R Magnesium regulates transcription of the mgtA magnesium transporter gene in Salmonella enterica serovar typhimurium via prolyl-bond formation during translation of the mgtL leader ORF.
Ganatra, Yash Yogesh Passive thermal management using phase change materials. Gangaraju, SricharanLochan Machine-to-machine communication for automatic retrieval of scientific data. Ganguly, Samiran Spintronic device modeling and evaluation using modular approach to spintronics. Gao, Jiejun Nanoparticle toxicity and molecular mechanisms in fish: A case study with silver nanoparticles. Gao, Mengqi Toner usage prediction. Gardner, Nathan W Investigation of an energetic coupling between ligand binding and protein folding. Garrity, Jordan M Design and analysis of a high performance valve.
Geesey, Bryce A Utilizing tunable signal interference control topologies with electromechanical resonators. Ge, Jiaqi Sequential pattern mining with uncertain data. Gentry, Patrick L A new reality: Funding formula changes and property tax caps and their effects on the role of the school superintendent in the state of Indiana. Gettings, Patricia E Understanding the communicative processes of baby boomer women adjusting to retirement: Connecting micro and macro discourses.
Ge, Yifan Investigating spatial distribution and dynamics of membrane proteins in polymer-tethered lipid bilayer systems using single molecule-sensitive imaging techniques. Ghahari, Seyedali The effect of ZnO nanoparticles on thermoelectric behavior and fresh properties of cement paste. Ghosh, Arnab Jyoti Analytical investigation of fretting wear with special emphasis on stress based models. Gilland, Kaitlyn Elizabeth Short-term effects of a Western diet on the number of brainderived neurotrophic factor immunoreactive neurons in the hypothalamic arcuate, ventromedial and paraventricular nuclei.
Glas, Zoe Elizabeth Mitigating conflict: A human dimensions analysis of mesopredators and their management. Glavin, Nicholas Robert Ultra-thin boron nitride films by pulsed laser deposition: Plasma diagnostics, synthesis, and device transport. Goblet, Valentine Pascale Phase of flight identification in general aviation operations. Lucian Soca. Gokhale, Vaibhav V Design of a helmet with an advanced layered composite for energy dissipation using a multi-material compliant mechanism synthesis. Gomes, Joan Implementation of i-vector algorithm in speech emotion recognition by using two different classifiers: Gaussian mixture model and support vector machine.
Goodcase, Eric T The role of attachment insecurity in preferred communication modality and relationship satisfaction of romantic relationships initiated online. Gradzewicz, Audrey D How small the apocalypse. Green, Colleen Warwick Bad girls in corsets: Women and the transgressive body in the nineteenth century. Greene, Frederick V The path towards clear and convincing digital privacy rights.
Griffin-Oliver, Courtney Janai Set and element-level compatibility of spatial and location-word stimuli paired to eye-movement, vocal, and keypress response modalities. Groen, Jessica A We'll find the time: Performing traumatic hope through fictions of child maltreatment.
Guidry, Brett W Finding the ghost with the machine: Breaking through the assessment center validity ceiling by exploring decisional processes using new sources of behavioral data within virtual assessments. Guo, Tian Effect of bioenergy crops and fast growing trees on hydrology and water quality in the Little Vermilion River Watershed. Guo, Tianqi The effect of confinement on the development of an axisymmetric wall jet in confined jet impingement. Guo, Xingye Thermomechanical properties of novel lanthanum zirconate based thermal barrier coatings - an integrated experimental and modeling study.
Gupta, Ravi Digital signal processors as HPC accelerator and performance tuning via static analysis and machine learning. Gupta, Rohinish Modelling and control of a parallel through-the-road plug-in hybrid vehicle. Gurule, Kaitlyn An analysis of digital forensic units. Guzzetti, Davide Coupled orbit-attitude mission design in the circular restricted three-body problem. Haderlie, Jacob C Modeling methods for merging computational and experimental aerodynamic pressure data.
Halimi, Ghulam Hazrat Can Afghanistan achieve self-sufficiency in wheat? Limitations due to market integration. Halimi, Ghulam Hazrat Trade and agriculture policy options to improve the wheat subsector in Afghanistan. Hall, Derrick R. Hammond, Max A The influence of collagen crosslinking and treadmill exercise on the mechanics, composition, and morphology of bone at multiple length scales.
Han, Arum How training set and prior knowledge affect preschoolers' perception of quantity and early number learning. Han, Chang Wan Characterization of heterogeneous catalysts using advanced transmission electron microscopy techniques. Haney, Alison M A matter of faith: The role of religion, doubt, and personality in emerging adult mental health.
Han, Jaemin Multi-session Network Coding characterization using new linear coding frameworks. Haria, Hiral Jayantilal A novel mode-switching hydraulic hybrid for an on-highway vehicle: A study of architecture and control. Harris, Mary Beth Women writers and the genealogy of the gentleman: masculinity, authority, and male characters in eighteenth-century English novels by women. Hassan, Khaled MD. Hawkins, Elizabeth Marie Organizing historical agricultural data and identifying data integrity zones to assess agricultural data quality.
Hay, Martha E Design of nitroxide-based radical polymer materials for electronic applications. Hayrapetian, Allenoush Analyzing and evaluating security features in software requirements. Hazlitt, Robert A Synthesis of a malvidinglucoside derivative with a difluoromethylene linkage. Heijnen, Michel J. H Failures in adaptive locomotion in healthy young adults. Heneghan, Joseph M The biology and management of waterhemp in Indiana. Hengge, Neal N Enzymatic liquefaction of untreated corn stover.
Herrera Perez, Ruth Marisol Influence of the 3D microenvironment on glioblastoma migration and drug response. He, Zijian Service-level based response by assignment and order processing for warehouse automation. Hickle, Mark D Synthesis, design, and fabrication techniques for reconfigurable microwave and millimeter-wave filters. Hinh, Robert Tool comparison of semantic parsers. Hinkel, Irina A What is contemporary art? Hjortland, Nicole M Defining the regulatory determinants in substrate catalysis by biochemical, biophysical, and kinetic studies for the development of specific small-molecule inhibitors of ubiquitin specific proteases 7 and Hodde, Whitney The effect of climate change on the economics of conservation tillage: A study based on field experiments in Indiana.
Hodson, Stephen L Carbon nanotube thermal interfaces and related applications. Hoggatt, Will Development of a fluidic mixing nozzle for 3D bioprinting. Holgate, Horane A Development and initial validation of a culturally responsive classroom climate scale. Hollandbeck, Gaelle Florence Effect of volunteer corn density on deoxynivalenol production by Fusarium graminearum in hybrid corn. Hollingshead, Nicole A Examining the influence of Hispanic ethnicity and ethnic bias on medical students' pain decisions.
Holzer, Corey T The application of natural language processing to open source intelligence for ontology development in the advanced persistent threat domain. Hoogewind, Kimberly A Climate change and hazardous convective weather in the United States: Insights from high-resolution dynamical downscaling. Houston, Saori M A longitudinal study of the development of fluency of novice Japanese learners: Analysis using objective measures.
Houtman, John A Design and plan of a modified hydroponic shipping container for research. Hou, Yangyang Low rank methods for optimizing clustering. Hrycik, Allison R Spatio-temporal diet variation and movement decisions of Lake Erie yellow perch. Huang, Hsin-Ying Examination and utilization of rare features in text classification of injury narratives.
Huang, Shouyuan Parametric and design analysis on thermoelectric generators. Huang, Wanfeng Concurrent detection and isolation of cellular and molecular biomarkers. Huang, Wenhan Parallelized ray casting volume rendering and 3D segmentation with combinatorial map. Huang, Yuqian Pattern exploration and event detection from geo-tagged tweets. Huang, Zhi Vehicle sensor-based pedestrian position identification in V2V environment.
Huang, Zun Wave propagation and imaging in structured optical media. Huckabee, Alexis G In-column polymer modifications: Advancing polymer bonded phases. Hudspeth, Matthew C Multi-axial failure of high-performance fiber during transverse impact. Hughes, Kyle M Gravity-assist trajectories to Venus, Mars, and the ice giants: Mission design with human and robotic applications. Hurt, Moriah J Evaluating the physical welfare of dogs in commercial breeding facilities in the United States.
Hussein, Ahmed Mohamed Abd-elhaffiez Effective memory management for mobile environments. Hu, Yaowu Laser shock imprinting of metallic nanostructures and shock processing of low-dimensional materials. Huynh, William B Gesture based non-obstacle interaction on mobile computing devices for dirty working environment.
Ibrahim, Md Phyllanthus niruri supplemented diet as a modulator of stress and immune responses in Nile tilapia, Oreochromis niloticus, reared in inland recirculating and aquaponics systems. Irven, Donovan Being and literature: The disclosure of place in modernity. Issa, Salah F Exploring the cause of injury or death in grain entrapment, engulfment and extrication.
Jacobs, Elin M Spatiotemporal patterns of hydroclimatic drivers and soil-water storage: Observations and modeling across scales. Jacobs, Nicholas L Analysis of feedback control applied with command shaping to minimize residual vibration. Jahan, Mafruha Options to improve energy efficiency for educational building. Jahan, Suchana Akter Optimization of conformal cooling channels in 3D printed plastic injection molds. James Stephen, Julian Securing cloud-based data analytics: A practical approach. Jarmusch, Alan Keith Ambient ionization - mass spectrometry: Advances toward intrasurgical cancer detection.
Jauregui, Luis A Electronic transport in nano-devices based on graphene and topological insulators. Javagal, Suhas Raveesh User-centric workload analytics: Towards better cluster management. Jeon, Bonggil A method for selecting HVAC retrofit solutions for existing small- and medium-sized commercial buildings. Jeong, Jun Young Analysis of structural and functional brain networks. Jiang, Zhengping Multi-scale simulations for high efficiency low power nanoelectronic devices. Jiao, Peng Dynamic green split optimization in intersection signal design for urban street network.
Jin, Jonghoon Fast and robust convolutional neural networks optimized for embedded platforms. Jin, Zhenong Crop modeling for assessing and mitigating the impacts of extreme climatic events on the US agriculture system. Ji, Yanzhu Transposable element and host dynamics in mammals and birds as revealed by transcriptomic and genomic evidence. Johnson, Scott C Observability and observer design for switched linear systems. Jones, Gavin Robert Accessible surface area of common silica particle types. Jones, Kyle E Hip hop, circulation, and the associational life of Peruvian youth.
Jung, Wonyeong Computational investigation of force generation, relaxation, and remodeling of the actin cytoskeleton. Kaczay, Kaitlin R A comparison of the efficacy of radiant and immersion frying using hash brown patties as a model food matrix. Kadasala, Naveen Reddy Synthesis, characterization, and application of magnetic gold nanoclusters. Kalyanam, Rajesh Interactive logical analysis of planning domains. Kambatla, Karthik Shashank Methods to improve applicability and efficiency of distributed data-centric compute frameworks.
Kanani, Geoffrey H An examination of how specific support structures impact the adjustment process of sub-Saharan African students in two Midwestern institutions of higher education. Utilitarian Situations. Kang, Jisun Improving a mesh segmentation algorithm based on non-negative matrix factorization.
Kang, Ji Yun Help-seeking intention among college students: Cross-cultural study between East Asian international students and domestic students in the Unites States. Karki, Anju Investigating the role of the basic helix-loop-helix transcription factor MIST1 in pancreatic diseases. Karyadi, Kenny A The effects of alcohol odor cues on food and alcohol attentional bias, cravings, and consumption. Kaseb, Ahmed S A cost-effective cloud-based system for analyzing big real-time visual data from thousands of network cameras. Katzman, Tanya Lynn The use of stable isotopes and particulate matter in the investigation of local and regional atmospheric chemistry.
Kebede, Ammanuiel A Asphalt pavement preservation using rejuvenating fog seals. Keith, Melissa G Autonomy and motivation: The impact of task difficulty. Keller, Christine E. M Biochemical changes in animal models of fetal alcohol spectrum disorder. Kendall, Jordan D Hydrocode modeling of oblique impacts into terrestrial planets.
Kesari, Aditi Factors affecting transduction efficiency of pseudotyped viral vectors incorporating alphaviral glycoproteins. Khan, Ishita K Protein function, diversity and functional interplay. The image shows a mixture of fine soil, rocks and substantial boulders that have rolled down the valley's slopes.
Credit: NASA or chalk. Because there has been no lunar tectonic activity or large-scale crustal movement, metamorphic rocks such as schist and gneiss, formed slowly through crustal pressure and heat, are not found on the Moon. Basalt, anorthosite and breccia make up the three main types of lunar rock. Basalt is a dark-colored volcanic rock that once flowed as lava and filled all the marial basins of the near side and some areas on the far side. Its grain size averages less than 1mm, an indication of its rapid cooling after extrusion. A basaltic rock taken from Mare Tranquillitatis.
The lunar maria are all composed of this dark type of rock, which flowed onto the Moon's surface more than 3 billion years ago. The most abundant Mg-suite rocks are norite plagioclase- pyroxene rock and troctolite plagioclase-olivine rock. The Mg-suite rocks date from around 4. Breccia is a composite rock made up of fragments created through the processes of impact shattering, mixing, melting and recrystallization of rock during the high energies released during meteoroid and asteroid impacts.
Typical breccias contain coarse fragments embedded in a fine-grained crystal matrix. Breccias are described as monomict if they contain fragments of only one rock type; most breccias are polymict and are composed of more than one type of rock. All three rock types - mare basalt, anorthositic material and breccia - can be found in any location on the Moon, though the proportions will vary, depending on whether the site is located in the highlands or a mare. Anorthosite makes up the Moon's highland crust, and is the oldest rock type found on the Moon.
This sample is 4. A small proportion of material found in any spot will come from much further afield, debris thrown out by distant impacts hundreds of kilometers away. Shaping the Moon's Surface Impact Much of the Moon has been intensely sculpted by meteoroidal and asteroidal impact. Through the eons, the substantial atmospheres of Venus, the Earth and Mars have served as an effective impact buffer, allowing only a few of the biggest incoming objects to wreak large-scale damage.
Atmosphereless Mercury and the Moon have been fully exposed to the harsh vacuum of space and subjected to bombardment by interplanetary dust, meteoroids, asteroids and comets, in addition to x-rays, gamma rays and cosmic rays. A breccia taken from the valley of Taurus Littrow. Lunar breccias are made up of fused fragments of material derived from impacts. This sample consists of fragments of glass, minerals and rock cemented together in a glassy matrix.
It has been esti- mated that around 3 trillion craters over a meter in diameter dot the lunar surface. Large tracts of the lunar surface have been modified by volcanic activity and other geological processes, including faulting. The lunar crust has never been subjected to any appreciable tectonic activity, and large-impact features many billions of years old can be clearly traced; some of them were actually formed before life on Earth appeared. The overwhelming majority of lunar craters display the hallmarks of impact formation. Leaving aside the evidence of the lunar rocks themselves, there is a clear pattern of impact-crater morphology spanning all size ranges, from the tiniest micrometeorite impact pits to the vast asteroidal impact basins.
The observed morphology of lunar craters perfectly matches computer studies of impacts, in addition to ballistic impact experiments performed in laboratories and field studies of terrestrial craters both natural impact features and manmade explosion craters. Many of the lunar rocks themselves could only have been formed as a result of the sudden high temperatures and pressures produced during impact events.
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There is no evidence to support the idea that any of the larger craters repre- sent the rims of ancient lunar volcanoes, nor is there any evidence to suggest that any major craters were formed by violent crustal explosions or as a result of crustal 19 The Moon's Origin The Moon's Origin Fig. A small number just a few dozen of meteorites found on Earth are known to be mate- rial that originated on the Moon, having been thrown from the lunar surface by the explosive power of impacts.
Only 0. This rare mate- rial may have been blasted from around 20 individual impact events during the past 10 million years. These tiny fragments of lunar-highland breccia and mare basalt, owned by the author, are chips from the catalogued lunar meteorites. Credit: Peter Grego collapse after magmatic subsidence. If some craters did happen to be volcanic in origin, then a number of these features, frozen in various stages of formation, would likely exist, but this has not been not observed.
The lunar surface is continually pelted with a rain of micrometeoroids a term applied to meteoroids smaller than 1 mm in diameter , with an average rate of one micrometeoroid impact per week per square meter. Though small, micro- meteoroids impact at very high velocities, ranging from a minimum of 2. The surfaces of lunar rocks studied under the microscope are indented with countless tiny impact pits, many of them surrounded by a splash pattern of melted material.
Rugged alpine landscapes cannot be found anywhere on the Moon. The giant 2,km-diameter South Pole-Aitken Basin can be easily discerned on the lunar far side. Only the largest meteoroids are capable of penetrating the regolith to the solid crust beneath. A meteoroid about 10 m across would be sufficient to penetrate the typically deep regolith in the highlands. The crust beneath the impactor is compressed and the surrounding material is pushed downwards and outwards. An ultrahot bubble of expanding molten material with a temperature of several million degrees is formed as the impactor and the surrounding rocks are nearly instantaneously vaporized.
The edge of the crater is deformed and uplifted as a plume of excavat- ed material, made up of vaporized rock and larger rock fragments, is blasted outwards from the impact site. The excavated material is distributed around the crater in an ejecta blanket. The first mate- rial to be ejected comprises material that was close to the focus of impact near the surface, and this high-velocity material is launched steeply above the surface to be deposited at great distances from the crater. As the impact progresses, deeper mate- rial is excavated, but the overall energy of the impact dissipates.
Stages in the formation of a large impact crater. The crust is compressed and shockwaves propagate outwards, fracturing the crust. A plume of ejecta is thrown up from the Moon's surface as the edge of the explosion cavity is deformed and uplifted. The crater enlarges as the ejecta sheet is thrown across the crater's surroundings.
The material originally nearer the surface is ejected furthest, while deeper bedrock is lobbed shorter distances from the rim. Craters smaller than about 10 km across are usually smooth, bowl-shaped depressions with rounded, raised rims, and they have an average depth of about one-tenth their diameter. They have simple ejecta collars, usually forming an area of rough terrain that extends to about a crater diameter away from the rim, beyond which can be found small secondary craters formed by the impact of larger frag- ments of debris excavated by the primary impact.
Such simple craters can be seen dotted all over the maria and on the floors of large, flooded craters. Larger-impact features generally have a smaller depth to diameter ratio and they display progres- sively more complex forms. They often have sharp rims and their floors are covered with mounds of debris that has slipped off the steep inner walls, giving the crater rim a distinctly scalloped or polygonal outline. Complex craters more than 20 km in diameter see Table 1. Beyond the rim there is a consid- erable amount of physical structure, including prominent radial ridges and grooves, in addition to secondary cratering caused by the impact of substantial chunks of excavated bedrock.
Secondary craters are simple mechanical-impact pits formed at a far lower velocity than the original impact. The amount of material excavated by these secondary impacts can actually exceed the volume of material thrown out during the original high-velocity impact, since low-velocity impactors tend to be more efficient excavators than high-energy ones, which generate vast quantities of excess heat. Streams of ejected debris can produce lines of craters arrayed radially around their parent crater. These features can consist of an uncon- nected series of craters of roughly similar size typically smaller than about one- twentieth the diameter of the parent crater , or in an interconnected chain of craters some of them highly elongated that runs a considerable distance across the surface.
Some secondary-impact crater chains are so tightly knit that they resemble rilles, and can be mistaken for such at first glance. Such are the dynamics of impact that these radial structures do not follow perfectly straight lines - secondary-chain craters can follow quite curved, even sinuous, paths over the surface. The best place to view the entire array of secondary-impact structures is around the mighty crater Copernicus, since the structures were carved out of generally rather level mare material only comparatively recently in lunar geo- logical terms. Many large young craters are surrounded by bright ray systems.
Rays occur where the regolith has been churned up by secondary impacts, exposing fresh material at the surface. Some rays actually have a distinctly different composition from the regolith that they overlie. Like fingerprints, no two lunar ray systems appear to be exactly alike. Some rays, like those around the little crater Linne in Mare Serenitatis, form near-circular halos.
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Others, like those around Kepler in Oceanus Procellarum, form a neat splash pattern that is equally bright all over. O 0 03 C 0 4 25 Mare Orientale itself. A substantial system of secondary-impact craters,many of which are arranged in radial chains, radiates around the Orientale basin. Some bright lunar rays spread in only one direction, either in a broad fan of material or in a number of searchlight-like lines, like the twin searchlight-like beams emanating from the crater Messier A in Mare Fecunditatis.
The ray systems of numerous large craters appear to commence a short distance away from the crater rim, the crater itself being surrounded by a dark collar of material. Erosion by meteoroids gradually churned up the ray material on the surface, fading it over time. Rays may only last a couple of billion years before being blended in with their surroundings. Craters larger than km in diameter are known as ringed basins. Larger basins up to km in diameter have a well- developed inner mountain ring but lack a central elevation. The largest impact structures found on the Moon are the multiringed basins.
These vast scars of Table 1. The rings may represent frozen waves of crustal mate- rial caused by the collapse of the original central uplift immediately after impact, and the outer rings of multiringed impact basins may be far larger than the origi- nal asteroid impact crater. Examples of the variation in the morphology of impact features of different sizes can best be seen on the far side, where there has been little overt volcanic activity and lava flooding to alter their appearance see Table 1. Basin formation imparted tremendously powerful seismic waves into the lunar crust, which traveled around the Moon to converge on the other side, immediately opposite the impact site.
The concentration of these seismic waves led to the formation of localized areas of chaotic terrain, where pre-existing structures were shaken to their foundations, producing a knobbly, textured landscape. This pecu- liar kind of topography can be found in and around the far-side crater Van de Graaf, a sizable basin km across whose walls were turned into piles of rubble by the seismic waves generated by the formation of the Imbrium basin 3.
Basin Flooding Welling up from the mantle, magmatic intrusions through weak points in the lunar crust have extruded onto the surface as basaltic lava flows. The mare lava erupted from about 4 to 3 billion years ago. Samples of mare basalt melted in the laboratory take on the consistency of motor oil, an extremely ductile substance that is capable of 28 Fig. Projection of the entire lunar surface. The central area bounded by lines is the Moon's near side.
Note the remarkable difference in the number of large, dark, lava-filled basins between the two lunar hemispheres. The maria were not flooded in one single episode - each mare is made up of a number of different layers of lava flows, and distinct strata can be seen in the walls of many small craters in the maria.
Different phases of lava flooding are quite evident telescopically, as many maria take on a patchwork appearance that suggests numerous phases of volcanic activity that erupted batches of lavas of slightly different chemical composition. Most of the marial lava flows were extruded in very large eruptions from extended volcanic vents dotted around the floors of ringed basins and larger impact craters. Masses of material flowed rapidly across the surface in broad sheets that traveled for hundreds of kilometers. Digging a little deeper will reveal a more complicated story regarding the lunar surface.
Since spectral analysis shows that these dark halos consist of mare basalt, these dark-halod impact craters provide evidence for ancient buried lava plains known as cryptomaria. The total area once occupied by cryptomaria may have amounted to as much as half that occupied by the visible maria. The area around Mare Crisium, Mare Marginis and Mare Smythii, extending to the Lomonosov- Fleming region just past the eastern limb, is dotted with dozens of small dark- halod craters, indicating the presence of deeply buried lava flows. Lunar Volcanoes As large-scale vulcanism dwindled, smaller volcanic vents gave rise to a variety of different features.
Even with such fluid lunar lava flows, domes built up when a balance had been struck between the supply of lava being erupted and the rate of cooling of the extruded material. Intermittent eruptions of volcanic ash and pyroclastic deposits produced steeper-sided volcanic cones. Low- viscosity lava, squeezed through very narrow volcanic vents, can produce fire foun- tains that spray a multitude of tiny droplets - successive eruptions are capable of building up quite steep-sided volcanic cones.
Formed by fast- flowing lava, Sinuous rilles originate at volcanic vents and meander downslope. Lunar domes are squat features that were built up by lava and ash deposition when the moon was volcani- cally active. Many display summit craters volcanic vents. Dorsa are the same color as the terrain around them, and they cannot be dis- cerned under a high Sun.
There are two basic types of dorsa. Many of the major dorsa appear to follow the outlines of the mare basins. In some cases - notably in Mare Imbrium - the highest points of the original inner ring structure actual- ly protrude through the wrinkle ridges to stand proudly above the surface as isolated peaks. Some mare wrinkles appear to indicate the presence of ancient, completely buried craters, such as Lamont in Mare Tranquillitatis. These features are likely to have formed when the surfaces of the newly formed maria contracted and compressed, buckling the surface.
A number of mare ridges are the remnants of ancient lava flows; numerous examples can be viewed in Mare Imbrium. These features, which often have broad, ill-defined points of origin, have very low profile and their margins often extend into multiple well-defined lobes.
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Cross-section through a lunar mare and its mountain border. Wrinkle ridges have a number of possible modes of formation, including mare contraction, topographic moulding to un- derlying features and vulcan- ism. Very fast flowing lava extruded from volcanic vents rapidly cut through the recently deposited mare lava flows. The vents are often circular and crater like with flat floors, sunk into the landscape without any appreciably raised rim. Having been formed by very runny lava, the channels always progress downhill, gradually diminishing in depth and width, although the overall slope of the landscape is not always evident.
Some sinuous rilles appear to cut across higher ground, in apparent defiance of gravity. However, this higher ground is more than likely to have arisen by crustal buckling or arching some time after the sinuous rilles had been cut. Their courses were later exposed when the fragile tunnel roofs collapsed, and the remnants of the original roof can be observed on the rille floor, some large house-sized fragments having survived the fall intact.
Unlike terrestrial river valleys, sinuous rilles do not have any outwash plains. Many beau- tiful examples of sinuous rilles can be found in the near-side maria and within some lava-filled craters. Vallis Schroteri is more than km long, averages km wide and measures up to 1, m deep in places.
Vallis Schroteri is of exceptional interest, since a smaller sinuous rille actually winds along the length of the main valley floor, formed when the source of lavas was dwindling. Nearby, the dozen or more components of the Rimae Aristarchus makes one of the finest groups of sinuous rilles. Crustal tension has caused the crust to crack, and the western block of crust has slipped down, leaving a prominent escarpment some 1 1 0 km long.
Credit: Peter Grego sections of the crust fractured and slumped in response to unbearable loads set up in the crust. Normal faults are the most commonly observed types of fault on the Moon, and result from crustal tension; as the crust is pulled apart, the rocks may deform to a certain degree, but there comes a point when the crust cracks. Fault planes are usually inclined and rarely vertical. One side of the fault slips down in relation to the other, producing a freshly exposed rock face called a fault-scarp.
Other clearly visible examples of normal faults can be found in the maria, where they show up well under low angles of illumination. Faults that have been produced in the lunar highlands tend not to have the clean-cut form of Rupes Recta. Rupes Altai is a normal fault that lies several hundred kilometers due east of the Straight Wall. When a block of crust lying between two parallel normal faults subsides, a feature known as a graben rille results. Such valleys are rather common on the Moon. Because their origins are deep-seated, graben rilles can cut cleanly through pre-existing hills, mountains and craters without altering their course.
By far the biggest lunar graben far too large to be termed a rille is Vallis Alpes, a spectacu- lar rift valley that cuts neatly across the lunar Alps. Vallis Alpes is km long and averages 10 km wide, with steep inner walls. Its flat lava-flooded floor, sunk about 1, m below the surrounding uplands, has a small lava-cut sinuous rille running down the middle.
Many prominent graben cut across lunar maria, parallel to mare borders; these are known as arcuate rilles because of their curving paths. Prominent arcuate rilles lie near the southwestern border of Mare Tranquillitatis and the western and southeastern border of Mare Humorum. Intricate systems of interconnected linear rilles can be found in some maria and within many larger craters.
Good examples include a beautiful set of rilles to the east of Triesnecker in Sinus Medii, those on the floors of Lacus Mortis and within the craters Gassendi 32 Fig. Vallis Alpes, a large rift valley in the lunar Alps, was caused when crustal tension caused two parallel faults to appear across the mountains; the crust between the faults subsequently dropped down.
This kind of feature is known as a graben, and many of the Moon's smaller linear and arcuate rilles were cau- sed in the same manner. Credit: Peter Grego and Posidonius. This may be a rare example of a hybrid rille - one that originally formed as a result of crustal tension but that later experienced volcanic activity along its length. Dark-halo craters are also found to lie along some linear rilles. New crustal material is supplied by the mantle as active volcanic ridges push oceanic plates apart, causing them to collide with continental crust at its margins.
The lunar crust can be considered to have existed as a single unit since its appearance shortly after the formation of the Moon. Most of the lunar mountains have been produced by impact processes or crustal movement following major impacts. Many of the bigger, generally unflooded far-side impact basins display central massifs and a system of concentric mountain rings. Its outer ring, km in diameter, is made up of the Montes Cordillera. There is a sharp transi- tion between the smooth plains bounded by the Cordilleras and the radially grooved, mountainous landscape beyond.
This impressively sculpted terrain, formed by the erosion and deposition of piles of debris ejected during the Orientale impact, superficially resembles a terrestrial mountainous landscape that has experienced erosion by an ice sheet. Lava flooding within the near-side impact basins has obliterated many of their internal mountain structures, but here and there peaks do rise abruptly above the flat marial plains, an example is like the nunataks, which protrude through the glaciers of Greenland.
It is thought that, within some of these perpetually shadow-filled craters, vast quantities of nearly pure water ice lie buried beneath the top layers of the lunar soil on the crater floors. The ice is probably concentrated in numerous small areas that cover a total of around 1, sq km at each pole. The estimated total mass of the lunar ice is more than 6 billion tons. As soon as sunlight warmed the surface, the ice lying on the surface would have sublimated again and escaped back into space, but the ice that had fallen in permanently shadow-filled craters would have remained.
The Moon possesses no appreciable atmos- phere. No clouds ever drift across the dark lunar skies, no rainfall ever dampens the gray lunar soil and not a breath of wind whips up the dry lunar dust. TLP have been reported in three basic forms: brief isolated flashes or pulses of light, red- or blue-colored glows and obscurations or darkenings of portions of the lunar surface.
Some TLP have been reported to temporarily masquerade as distinct 3-dimensional topographic features. Such bouts of anomalous short-lived activity seem to occur sporadically in a number of specific small areas of the lunar surface. Among the areas most reportedly prone to TLP are the region in and around the bright crater Aristarchus in Oceanus Procellarum, the large flat-floored crater Plato in the lunar Alps, the borders of Mare Crisium, Mare Serenitatis and Mare Imbrium, and a number of craters with faulted floors, notably Alphonsus, Gassendi and Posidonius.
Lunar scientists have been reluctant to accept that our satellite occasionally displays such very obvious signs of activity, and this lack of widespread recog- nition of the reality of TLP has a great deal to do with the fact that they have been observed mainly by amateur astronomers with limited equipment. Few amateurs have been able to secure a photographic record of TLP, let alone employ anything as sophisticated as a spectroscope during these events when they have occurred.
The majority of TLP have therefore been inadequately recorded, at least for the purposes of later in-depth scientific analysis. Possible Causes of TLP Features on the Moon appear to change considerably during the 2-week-long lunar day as their angle of illumination by the Sun slowly changes.
A topographic feature 35 The Moon's Origin The Moon's Origin that may appear bold and conspicuous when illuminated by a low morning or evening Sun can fade into utter obscurity at lunar midday. Conversely, some albedo features are quite invisible when near the morning or evening termina- tor, but stand out boldly under a high Sun.
In addition, the observed brightness of albedo features is dependent on the height above the lunar surface of both the Sun and the observer on the Earth the selenographic longitude and latitude of the Sun and the observer. A feature observed under a midday Sun on one luna- tion may appear somewhat brighter or dimmer during the following lunation at midday.
The appearance of Aristarchus, one of the most brilliant lunar features, on the unilluminated side of the Moon, can be striking, and it has been the cause of many reported TLP. Thermoluminescence is caused when certain crystalline materials emit light when they are heated as excited electrons fall back to their ground state , but the amount of light given off by lunar thermoluminescence is entirely incapable of being detected by amateur instruments, and the process certainly would not explain any reported TLP.
There have been reports of TLP in the form of localized brightenings taking place at the same time as the arrival of high-energy solar particles emanating from solar flares. These brightenings have been ascribed to the lunar rocks fluorescing as the solar particles impacted on them. Again, the fluorescence of lunar materials is thought to take place, but it is incapable of producing sufficient light to be detected from the Earth. Finally, the Moon is not painted entirely in shades of gray.
Some areas of the Moon do possess delicate, but noticeable, coloration, and the observed intensity of these colors varies with their illumination. A full Moon high in the sky creates the opportunity to scan the Moon and view its large-scale coloration, and a low- to medium-power eyepiece without a filter on a telescope that is relatively free from chromatic aberration a Newtonian reflector, apo chromatic refractor or Maksutov catadioptric is recommended.
Achromatic refractors introduce a degree of false color, not usually a problem when the observer is studying topography alone, but distracting if a TLP search is being attempted. Although the lunar southern highlands are bright and gen- erally color-free, there is a surprising amount of color to be made out in the lunar maria.
One of the best color contrasts can be seen by viewing the adjacent seas of the reddish Mare Serenitatis and the distinctly blue Mare Tranquillitatis. Even using a good telescope under ideal conditions, the inexperienced lunar observer may not expect to see obvious hues of purple, brown, red, green and blue on the Moon, and their presence may wrongly be ascribed to some kind of anomalous event.
Thus, regularly occurring changes in the angle of illumination and the apparent brightness and colors of features can lead an inexperienced observer to draw the wrong conclusion - that a real change has taken place on the Moon. Some of the short-lived flashes that have been observed in random areas around the Moon may have been caused by meteoroid impacts on the lunar surface. Even a relatively small meteoroid impact would be sufficient to produce a brief flash visible in amateur telescopes, and such an event would be more readily visible were it to take place in the unilluminated portion of the Moon.
Nobody doubts that the Moon is hit from time to time by large meteoroids, and that impact flashes bright enough to be telescopically observed are produced, but the suggestion that meteor streams contain individual meteoroidal masses large enough to produce observable impact flashes on the Moon is controversial. It is widely accepted that meteor streams are almost exclusively composed of fragile grains of dust blown out by cometary nuclei, and contain nothing of a size large enough to produce any observable effects on the Moon, however brief. Meteorites found on the Earth have been shown to originate from asteroids, with a few that are known to have been blasted from the Moon and Mars.
There are only a few examples of terrestrial meteorite falls having taken place during the peaks of meteor showers, but these have been coincidental events: an examination of these meteorites shows them to be entirely unconnected with the parent body of the meteor stream. Material thrown up by any sizable meteoroid impact on the Moon would form an expanding shell of material that may itself remain visible for several minutes, especially if the focus of impact happens to lie just beyond the terminator and the ejecta cloud climbs high enough above the lunar surface to be directly illuminated by the Sun.
However, no reported TLP flash site has ever yielded a new crater that has been detected from the Earth. Such a sudden temperature change, as the Moon warms up in the morning sunshine and cools down at lunar dusk, takes place twice every 37 The Moon's Origin The Moon's Origin lunation. The processes of thermal shock, restricted to the materials in the very top layers of the regolith, cannot possibly give rise to any effects observ- able from the Earth. It is probably no coincidence that most TLP activity takes place in areas that have succumbed to substantial crustal stress and display extensive, deep-seated faulting - around mare borders and on the fractured floors of some craters.
In fact, the tidal pull of the Earth on the Moon is An escape of gases in itself may not give rise to any immediately observable effects, although it would be detectable spectroscopically. An energetic venting of gas may cause large volumes of the smaller particles in the loose upper few centimeters of the lunar soil to waft high into the lunar skies, causing a temporary obscuration of localized surface features as viewed from the Earth.
A large cloud of lunar dust might take on the appearance of a temporary hill for a few minutes, able to block enough sunlight for it to cast a shadow before the material gradually settles back on the lunar surface. Were such an event to take place on the night side of the Moon, just past the morning or evening terminator, the cloud might rise high enough to catch the rays of the Sun, creating a temporary bright spot in the darkness.
Volcanic eruptions on Earth that throw up vast clouds of fine debris are often illuminated with flashes of lightning.
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Within the dust cloud, a triboelectric charge is built up as the particles rub against each other, and lightning occurs when there are triboelectric discharges. Two other mechan- isms might cause a gaseous lunar eruption to glow. When rock crystals are subject- ed to mechanical strain, an electric potential appears across the crystal faces, causing a glow when this electricity is discharged into surrounding gases. Alternatively, protons and ultraviolet radiation in the solar wind are capable of exciting the atoms in the vented gases, ionizing them to produce a glow discharge.
Physical Lunar Changes In addition to elusive bouts of short-lived TLP activity, lunar changes of a perma- nent nature have also been suggested; there are a number of alleged cases. A great deal of controversy has surrounded claims of permanent change visible from the Earth, and evidence in their favor has often been weak and unreliable. Advocates of lunar change, attempting to establish a degree of respectability in their field, have been unfortunately hindered by the opinions of cranks and the spurious observations of charlatans.
Photography provides the firmest kind of evidence, yet 38 there has not been a single reliable photograph taken from the Earth that proves that permanent lunar change has taken place. Crater Linne, km off the western coastline of Mare Serenitatis, is a tiny 2. Linne is easily visible in binoculars and small telescopes.
When the area is illuminated by a low early morning or late afternoon Sun, a mm telescope should be just sufficient to resolve the tiny crater itself. It has been claimed that Linne was once a much larger crater - as large as 10 km across - and somehow it had shrunk in size. These assertions were sensationalist and based on poor science. A close look at the body of evidence pointing towards a once-large Linne will show that the case rests on flimsy foundations.
Old general maps, full of other glaring errors in cartography, can hardly be used as evidence, and many historical observations of Linne are contradictory. Linne has not changed appreciably since its formation, perhaps several hundred million years ago. Around km off the western shore of Mare Fecunditatis lie a pair of small craters positioned side-by-side on the marial plain.
The smaller of the two is Messier, a crater elongated in an east-west direction, measuring 9x11 km. Its neighbor, Messier A, measures 13 x 11 km, and has a more distorted shape owing to an extended nearly double western rim. A straight and narrow double ray extends like a searchlight beam from Messier A across to the hills marking the mare border. The Messier pair, fraternal rather than identical twins, make a pleas- ant sight through any telescope. They provide a good example of how the appear- ance of a lunar feature can alter considerably during a lunar day because of the changing angle of illumination, as anyone who has observed them under a variety of lighting conditions can testify.
Throughout the lunar day, the Messier twins can appear to shrink in diameter, assume distinctly nonelliptical shapes, alternate in size Messier sometimes looking as though it is the larger or even merge into one; the rays that emanate from Messier A also undergo changes in apparent brilliance. These are all tricks of the light that can lead the inexperienced observer to conclude that a real metamorphosis has taken place. Physical change does happen on the Moon, but on a scale that is usually un- observable through telescopes on Earth. For example, close-up orbiter photographs of the central hills of the crater Vitello show two sizable boulders, the larger of which is around 25 m in diameter; both objects made distinct tracks in the lunar soil as they rolled down the slope.
The boulders must have been jarred from their original perches by a large moonquake - a vigor- ous shaking of the lunar crust that perhaps resulted from a large meteoritic impact close to Vitello. Using photographs alone, it is impossible to determine the precise date on which the boulders made their short journeys: they could have rolled a moment before the probe took its pictures, or they may have tumbled down the hill many thousands of years ago.
The incredibly slow pace of erosion on the Moon, chiefly caused by a steady drizzle of micrometeorites, means that the tracks impressed in the soil are likely to remain fresh-looking for thousands of years to come. High-resolution photographs taken by orbiting probes have uncovered many more examples of small, localized physical changes due to migrating surface debris. Another mechanism of dust transport may be taking place on the Moon. The lunar soil has low conductivity, is readily charged and retains its electrical charge for long periods.
It is possible that charged particles in the solar wind, along with ultraviolet radiation, electrostati- cally charges the lunar soil, resulting in the levitation perhaps to heights of several kilometers and the transportation of small dust particles along the slowly moving boundary of the terminator. With its extreme clinginess, this charged material may present a hazard to future human lunar exploration. Averaging out the global topography of the lowland basins and mountainous highlands, the figure of the Fig.
Comparison between the Earth and Moon, showing their internal structures. The Earth has a relatively thin, mobile crust underlain by a hot, dynamic mantle and a large hot, iron, core. The Moon has a relatively thick, static crust and a warm interior, with a very small core.
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However, the Moon has a mass of 73, trillion tons, which amounts to just 1. If both the Earth and Moon were shrunk to the size of tennis balls, the wet blue one would weigh g and the dusty gray one would weigh g. On the Moon, an object weighs only about one sixth its terrestrial weight, and when dropped will fall to the lunar surface with 6 times less acceleration due to gravity. To leave the surface of the Moon and enter into lunar orbit or beyond , an object must travel at an escape velocity of 2. Escape velocity can be reached through the gradual acceleration produced by a rocket engine, or by sudden means - say, during an asteroidal impact that launches some of its ejecta into space.
All bodies, therefore, weigh about six times as much on the earth as they would upon the moon; or, rather, a body transferred to the moon's surface would weigh only about one-sixth of what it did on the terrestrial surface. It will therefore be seen that if a body of given mass were to be placed upon planet after planet in turn, its weight would regularly alter according to the force of gravity at each planet's surface.
Gravitation is indeed one of the greatest mysteries of nature. What it is, the means by which it acts, or why such a force should exist at all, are questions to which so far we have not had even the merest hint of an answer. Its action across space appears to be instantaneous. The intensity of gravitation is said in mathematical parlance "to vary inversely with the square of the distance.
At four times the distance, therefore, it will be one-sixteenth as strong. At the earth's surface a body is pulled by the earth's gravitation, or "falls," as we ordinarily term it, through 16 feet in one second of time; whereas at the distance of the moon the attraction of the earth is so very much weakened that a body would take as long as one minute to fall through the same space. Newton's investigations showed that if a body were to be placed at rest in space entirely away from the attraction of any other body it would remain always in a motionless condition, because there would plainly be no reason why it should move in any one direction rather than in another.
And, similarly, if a body were to be projected in a certain direction and at a certain speed, it would move always in the same direction and at the same speed so long as it did not come within the gravitational attraction of any other body. The possibility of an interaction between the celestial orbs had occurred to astronomers before the time of Newton; for instance, in the ninth century to the Arabian Musa-ben-Shakir, to Camillus Agrippa in , and to Kepler, who suspected its existence from observation of the tides.
Horrox also, writing in , spoke of the moon as moved by an emanation from the earth. But no one prior to Newton attempted to examine the question from a mathematical standpoint. Notwithstanding the acknowledged truth and far-reaching scope of the law of gravitation—for we find its effects exemplified in every portion of the universe—there [Pg 45] are yet some minor movements which it does not account for. For instance, there are small irregularities in the movement of Mercury which cannot be explained by the influence of possible intra-Mercurial planets, and similarly there are slight unaccountable deviations in the motions of our neighbour the Moon.
Up to this we have merely taken a general view of the solar system—a bird's-eye view, so to speak, from space. In the course of our inquiry we noted in a rough way the relative distances at which the various planets move around the sun. But we have not yet stated what these distances actually are, and it were therefore well now to turn our attention to this important matter. Each of us has a fair idea of what a mile is. It is a quarter of an hour's sharp walk, for instance; or yonder village or building, we know, lies such and such a number of miles away.
The measurements which have already been given of the diameters of the various bodies of the solar system appear very great to us, who find that a walk of a few miles at a time taxes our strength; but they are a mere nothing when we consider the distances from the sun at which the various planets revolve in their orbits. The following table gives these distances in round numbers. As here stated they are what are called "mean" distances; for, as the orbits are oval, the planets vary in their distances from the sun, and [Pg 47] we are therefore obliged to strike a kind of average for each case:—.
From the above it will be seen at a glance that we have entered upon a still greater scale of distance than in dealing with the diameters of the various bodies of the system. In that case the distances were limited to thousands of miles; in this, however, we have to deal with millions. A million being ten hundred thousand, it will be noticed that even the diameter of the huge sun is well under a million miles. How indeed are we to get a grasp of such distances, when those to which we are ordinarily accustomed—the few miles' walk, the little stretch of sea or land which we gaze upon around us—are so utterly minute in comparison?
The fact is, that though men may think that they can picture in their minds such immense distances, they actually can not. In matters like these we unconsciously employ a kind of convention, and we estimate a thing as being two or three or more times the size of another. More than this we are unable to do. For instance, our ordinary experience of a mile enables us to judge, in a way, of a stretch of several miles, such [Pg 48] as one can take in with a glance; but in our estimation of a thousand miles, or even of one hundred, we are driven back upon a mental trick, so to speak.
In our attempts to realise such immense distances as those in the solar system we are obliged to have recourse to analogies; to comparisons with other and simpler facts, though this is at the best a mere self-cheating device. The analogy which seems most suited to our purpose here, and one which has often been employed by writers, is borrowed from the rate at which an express train travels.
Let us imagine, for instance, that we possess an express train which is capable of running anywhere, never stops, never requires fuel, and always goes along at sixty miles an hour. Suppose we commence by employing it to gauge the size of our own planet, the earth. Let us send it on a trip around the equator, the span of which is about 24, miles. At its sixty-miles-an-hour rate of going, this journey will take nearly 17 days. Next let us send it from the earth to the moon.
This distance, , miles, being ten times as great as the last, will of course take ten times as long to cover, namely, days; that is to say, nearly half a year. Again, let us send it still further afield, to the sun, for example. Here, however, it enters upon a journey which is not to be measured in thousands of miles, as the others were, but in millions. The distance from the earth to the sun, as we have seen in the foregoing table, is about 93 millions of miles. Our express train would take about years to traverse this.
Having arrived at the sun, let us suppose that our [Pg 49] train makes a tour right round it. This will take more than five years. Supposing, finally, that our train were started from the sun, and made to run straight out to the known boundaries of the solar system, that is to say, as far as the orbit of Neptune, it would take over years to traverse the distance. That sixty miles an hour is a very great speed any one, I think, will admit who has stood upon the platform of a country station while one of the great mail trains has dashed past.
But are not the immensities of space appalling to contemplate, when one realises that a body moving incessantly at such a rate would take so long as 10, years to traverse merely the breadth of our solar system? Ten thousand years! Just try to conceive it. Why, it is only a little more than half that time since the Pyramids were built, and they mark for us the Dawn of History.
And since then half-a-dozen mighty empires have come and gone! Having thus concluded our general survey of the appearance and dimensions of the solar system, let us next inquire into its position and size in relation to what we call the Universe. A mere glance at the night sky, when it is free from clouds, shows us that in every direction there are stars; and this holds good, no matter what portion of the globe we visit.
The same is really true of the sky by day, though in that case we cannot actually see the stars, for their light is quite overpowered by the dazzling light of the sun. We thus reach the conclusion that our earth, that our solar system in fact, lies plunged within the midst [Pg 50] of a great tangle of stars. What position, by the way, do we occupy in this mighty maze? Are we at the centre, or anywhere near the centre, or where?
It has been indeed amply proved by astronomical research that the stars are bodies giving off a light of their own, just as our sun does; that they are in fact suns, and that our sun is merely one, perhaps indeed a very unimportant member, of this great universe of stars. Each of these stars, or suns, besides, may be the centre of a system similar to what we call our solar system, comprising planets and satellites, comets and meteors;—or perchance indeed some further variety of attendant bodies of which we have no example in our tiny corner of space.
But as to whether one is right in a conjecture of this kind, there is up to the present no proof whatever. No telescope has yet shown a planet in attendance upon one of these distant suns; for such bodies, even if they do exist, are entirely out of the range of our mightiest instruments. On what then can we ground such an assumption?
Merely upon analogy; upon the common-sense deduction that as the stars have characteristics similar to our particular star, the sun, it would seem unlikely that ours should be the only such body in the whole of space which is attended by a planetary system. There is in fact no background at all. The brilliant orbs are all around us in space, at different distances from us and from each other; and we can gaze between them out into the blackness of the void [Pg 51] which, perhaps, continues to extend unceasingly long after the very outposts of the stellar universe has been left behind.
Shall we then start our imaginary express train once more, and send it out towards the nearest of the stars? This would, however, be a useless experiment. Our express-train method of gauging space would fail miserably in the attempt to bring home to us the mighty gulf by which we are now faced. Let us therefore halt for a moment and look back upon the orders of distance with which we have been dealing. First of all we dealt with thousands of miles. Next we saw how they shrank into insignificance when we embarked upon millions.
We found, indeed, that our sixty-mile-an-hour train, rushing along without ceasing, would consume nearly the whole of historical time in a journey from the sun to Neptune. In the spaces beyond the solar system we are faced, however, by a new order of distance. From sun to planets is measured in millions of miles, but from sun to sun is measured in billions. But does the mere stating of this fact convey anything? I fear not. For the word "billion" runs as glibly off the tongue as "million," and both are so wholly unrealisable by us that the actual difference between them might easily pass unnoticed.
Let us, however, make a careful comparison. What is a million? It is a thousand thousands. But what is a billion? It is a million millions.
Consider for a moment! A million of millions. That means a million, each unit of which is again a million. In fact every separate "1" in this million is itself a million. Here is a way of trying to realise this [Pg 52] gigantic number. A million seconds make only eleven and a half days and nights. But a billion seconds will make actually more than thirty thousand years! Having accepted this, let us try and probe with our express train even a little of the new gulf which now lies before us. At our old rate of going it took almost two years to cover a million miles.
To cover a billion miles—that is to say, a million times this distance—would thus take of course nearly two million years. Alpha Centauri, the nearest star to our earth, is some twenty-five billions of miles away. Our express train would thus take about fifty millions of years to reach it! This shows how useless our illustration, appropriate though it seemed for interplanetary space, becomes when applied to the interstellar spaces. It merely gives us millions in return for billions; and so the mind, driven in upon itself, whirls round and round like a squirrel in its revolving cage.
There is, however, a useful illustration still left us, and it is the one which astronomers usually employ in dealing with the distances of the stars. The illustration in question is taken from the velocity of light. Light travels at the tremendous speed of about , miles a second. It therefore takes only about a second and a quarter to come to us from the moon. It traverses the 93,, of miles which separate us from the sun in about eight minutes. It travels from the sun out to Neptune in about four hours, which means that it would cross the solar system from end to end in eight.
To pass, however, across the distance which separates us from Alpha Centauri [Pg 53] it would take so long as about four and a quarter years! Astronomers, therefore, agree in estimating the distances of the stars from the point of view of the time which light would take to pass from them to our earth. They speak of that distance which light takes a year to traverse as a "light year. Now as the rays of light coming from Alpha Centauri to us are chasing one another incessantly across the gulf of space, and as each ray left that star some four years before it reaches us, our view of the star itself must therefore be always some four years old.
Were then this star to be suddenly removed from the universe at any moment, we should continue to see it still in its place in the sky for some four years more, after which it would suddenly disappear. The rays which had already started upon their journey towards our earth must indeed continue travelling, and reaching us in their turn until the last one had arrived; after which no more would come.
We have drawn attention to Alpha Centauri as the nearest of the stars. The majority of the others indeed are ever so much farther. We can only hazard a guess at the time it takes for the rays from many of them to reach our globe. Suppose, for instance, we see a sudden change in the light of any of these remote stars, we are inclined to ask ourselves when that change did actually occur. Was it in the days of Queen Elizabeth, or at the time of the Norman Conquest; or was it when Rome was at the height of her glory, or perhaps ages before that when the Pyramids [Pg 54] of Egypt were being built?
Even the last of these suppositions cannot be treated lightly. We have indeed no real knowledge of the distance from us of those stars which our giant telescopes have brought into view out of the depths of the celestial spaces. Had the telescope never been invented our knowledge of astronomy would be trifling indeed. Prior to the year , when Galileo first turned the new instrument upon the sky, all that men knew of the starry realms was gathered from observation with their own eyes unaided by any artificial means.
In such researches they had been very much at a disadvantage. The sun and moon, in their opinion, were no doubt the largest bodies in the heavens, for the mere reason that they looked so! The mighty solar disturbances, which are now such common-places to us, were then quite undreamed of.
The moon displayed a patchy surface, and that was all; her craters and ring-mountains were surprises as yet in store for men. Nothing of course was known about the surfaces of the planets. These objects had indeed no particular characteristics to distinguish them from the great host of the stars, except that they continually changed their positions in the sky while the rest did not.
The stars themselves were considered as fixed inalterably upon the vault of heaven. The sun, moon, and planets apparently moved about in the intermediate space, supported in their courses by strange and fanciful devices. The idea of satellites was as yet unknown. Comets were regarded as [Pg 56] celestial portents, and meteors as small conflagrations taking place in the upper air. In the entire absence of any knowledge with regard to the actual sizes and distances of the various celestial bodies, men naturally considered them as small; and, concluding that they were comparatively near, assigned to them in consequence a permanent connection with terrestrial affairs.
Thus arose the quaint and erroneous beliefs of astrology, according to which the events which took place upon our earth were considered to depend upon the various positions in which the planets, for instance, found themselves from time to time. It must, however, be acknowledged that the study of astrology, fallacious though its conclusions were, indirectly performed a great service to astronomy by reason of the accurate observations and diligent study of the stars which it entailed.
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We will now inquire into the means by which the distances and sizes of the celestial orbs have been ascertained, and see how it was that the ancients were so entirely in the dark in this matter. There are two distinct methods of finding out the distance at which any object happens to be situated from us. The other is by moving oneself a little to the right or left, and observing whether the distant object appears in any degree altered in position by our own change of place.
One of the best illustrations of this relative change of position which objects undergo as a result of our own change of place, is to observe the landscape from the [Pg 57] window of a moving railway carriage. As we are borne rapidly along we notice that the telegraph posts which are set close to the line appear to fly past us in the contrary direction; the trees, houses, and other things beyond go by too, but not so fast; objects a good way off displace slowly; while some spire, or tall landmark, in the far distance appears to remain unmoved during a comparatively long time.
Actual change of position on our own part is found indeed to be invariably accompanied by an apparent displacement of the objects about us, such apparent displacement as a result of our own change of position being known as "parallax. Thus it comes to pass that distances can be measured without the necessity of moving over them; and the breadth of a river, for instance, or the distance from us of a ship at sea, can be found merely by such means. It is by the application of this principle to the wider field of the sky that we are able to ascertain the distance of celestial bodies.
We have noted that it requires a goodly change of place on our own part to shift the position in which some object in the far distance is seen by us. To two persons separated by, say, a few hundred yards, a ship upon the horizon will appear pretty much in the same direction.
They would require, in fact, to be much farther apart in order to displace it sufficiently for the purpose of estimating their distance from it. It [Pg 58] is the same with regard to the moon. Two observers, standing upon our earth, will require to be some thousands of miles apart in order to see the position of our satellite sufficiently altered with regard to the starry background, to give the necessary data upon which to ground their calculations. The change of position thus offered by one side of the earth's surface at a time is, however, not sufficient to displace any but the nearest celestial bodies.
When we have occasion to go farther afield we have to seek a greater change of place. This we can get as a consequence of the earth's movement around the sun. Observations, taken several days apart, will show the effect of the earth's change of place during the interval upon the positions of the other bodies of our system. But when we desire to sound the depths of space beyond, and to reach out to measure the distance of the nearest star, we find ourselves at once thrown upon the greatest change of place which we can possibly hope for; and this we get during the long journey of many millions of miles which our earth performs around the sun during the course of each year.
But even this last change of place, great as it seems in comparison with terrestrial measurements, is insufficient to show anything more than the tiniest displacements in a paltry forty-three out of the entire host of the stars. We can thus realise at what a disadvantage the ancients were.
The measuring instruments at their command were utterly inadequate to detect such small displacements. It was reserved for the telescope to reveal them; and even then it required the great telescopes of recent times to show the [Pg 59] slight changes in the position of the nearer stars, which were caused by the earth's being at one time at one end of its orbit, and some six months later at the other end—stations separated from each other by a gulf of about one hundred and eighty-six millions of miles. The actual distances of certain celestial bodies being thus ascertainable, it becomes a matter of no great difficulty to determine the actual sizes of the measurable ones.
It is a matter of everyday experience that the size which any object appears to have, depends exactly upon the distance it is from us. The farther off it is the smaller it looks; the nearer it is the bigger. If, then, an object which lies at a known distance from us looks such and such a size, we can of course ascertain its real dimensions. Take the moon, for instance. As we have already shown, we are able to ascertain its distance. We observe also that it looks a certain size.
It is therefore only a matter of calculation to find what its actual dimensions should be, in order that it may look that size at that distance away. Similarly we can ascertain the real dimensions of the sun. The planets, appearing to us as points of light, seem at first to offer a difficulty; but, by means of the telescope, we can bring them, as it were, so much nearer to us, that their broad expanses may be seen. We fail, however, signally with regard to the stars; for they are so very distant, and therefore such tiny points of light, that our mightiest telescopes cannot magnify them sufficiently to show any breadth of surface.
Instead of saying that an object looks a certain [Pg 60] breadth across, such as a yard or a foot, a statement which would really mean nothing, astronomers speak of it as measuring a certain angle. Such angles are estimated in what are called "degrees of arc"; each degree being divided into sixty minutes, and each minute again into sixty seconds. Popularly considered the moon and sun look about the same size, or, as an astronomer would put it, they measure about the same angle.
This is an angle, roughly, of thirty-two minutes of arc; that is to say, slightly more than half a degree. The broad expanse of surface which a celestial body shows to us, whether to the naked eye, as in the case of the sun and moon, or in the telescope, as in the case of other members of our system, is technically known as its "disc. Since some members of the solar system are nearer to us than others, and all are again much nearer than any of the stars, it must often happen that one celestial body will pass between us and another, and thus intercept its light for a while.
The moon, being the nearest object in the universe, will, of course, during its motion across the sky, temporarily blot out every one of the others which happen to lie in its path. When it passes in this manner across the face of the sun, it is said to eclipse it. When it thus hides a planet or star, it is said to occult it. The reason why a separate term is used for what is merely a case of obscuring light in exactly the same way, will be plain when one considers that the disc of the sun is almost of the same apparent size as that of the moon, and so the complete hiding of the sun can last but a few minutes at the most; whereas a planet or a star looks so very small in comparison, that it is always entirely swallowed up for some time when it passes behind the body of our satellite.
The sun, of course, occults planets and stars in exactly the same manner as the moon does, but we cannot see these occultations on account of the blaze of sunlight. By reason of the small size which the planets look [Pg 62] when viewed with the naked eye, we are not able to note them in the act of passing over stars and so blotting them out; but such occurrences may be seen in the telescope, for the planetary bodies then display broad discs. There is yet another occurrence of the same class which is known as a transit.
This takes place when an apparently small body passes across the face of an apparently large one, the phenomenon being in fact the exact reverse of an occultation. As there is no appreciable body nearer to us than the moon, we can never see anything in transit across her disc. But since the planets Venus and Mercury are both nearer to us than the sun, they will occasionally be seen to pass across his face, and thus we get the well-known phenomena called Transits of Venus and Transits of Mercury.
As the satellites of Jupiter are continually revolving around him, they will often pass behind or across his disc. Such occultations and transits of satellites can be well observed in the telescope. There is, however, a way in which the light of a celestial body may be obscured without the necessity of its being hidden from us by one nearer. It will no doubt be granted that any opaque object casts a shadow when a strong light falls directly upon it. Thus the earth, under the powerful light which is directed upon it from the sun, casts an extensive shadow, though we are not aware of the existence of this shadow until it falls upon something.
The shadow which the earth casts is indeed not noticeable to us until some celestial body passes into it. As the sun is very large, and the earth in comparison very [Pg 63] small, the shadow thrown by the earth is comparatively short, and reaches out in space for only about a million miles. There is no visible object except the moon, which circulates within that distance from our globe, and therefore she is the only body which can pass into this shadow.
Whenever such a thing happens, her surface at once becomes dark, for the reason that she never emits any light of her own, but merely reflects that of the sun. As the moon is continually revolving around the earth, one would be inclined to imagine that once in every month, namely at what is called full moon , when she is on the other side of the earth with respect to the sun, she ought to pass through the shadow in question.
But this does not occur every time, because the moon's orbit is not quite upon the same plane with the earth's. It thus happens that time after time the moon passes clear of the earth's shadow, sometimes above it, and sometimes below it. It is indeed only at intervals of about six months that the moon can be thus obscured. This darkening of her light is known as an eclipse of the moon. It seems a great pity that custom should oblige us to employ the one term "eclipse" for this and also for the quite different occurrence, an eclipse of the sun; in which the sun's face is hidden as a consequence of the moon's body coming directly between it and our eyes.
The popular mind seems always to have found it more difficult to grasp the causes of an eclipse of the moon than an eclipse of the sun. As Mr. Gore  puts it: "The darkening of the sun's light by the interposition of the moon's body seems more [Pg 64] obvious than the passing of the moon through the earth's shadow. Eclipses of the moon furnish striking spectacles, but really add little to our knowledge. They exhibit, however, one of the most remarkable evidences of the globular shape of our earth; for the outline of its shadow when seen creeping over the moon's surface is always circular.
Eclipses of the Moon , or Lunar Eclipses, as they are also called, are of two kinds— Total , and Partial. In a total lunar eclipse the moon passes entirely into the earth's shadow, and the whole of her surface is consequently darkened. This darkening lasts for about two hours. In a partial lunar eclipse, a portion only of the moon passes through the shadow, and so only part of her surface is darkened see Fig.
A very striking phenomenon during a total eclipse of the moon, is that the darkening of the lunar surface is usually by no means so intense as one would expect, when one considers that the sunlight at that time should be wholly cut off from it. The occasions indeed upon which the moon has completely [Pg 65] disappeared from view during the progress of a total lunar eclipse are very rare.
On the majority of these occasions she has appeared of a coppery-red colour, while sometimes she has assumed an ashen hue. The explanations of these variations of colour is to be found in the then state of the atmosphere which surrounds our earth. When those portions of our earth's atmosphere through which the sun's rays have to filter on their way towards the moon are free from watery vapour, the lunar surface will be tinged with a reddish light, such as we ordinarily experience at sunset when our air is dry.
The ashen colour is the result of our atmosphere being laden with watery vapour, and is similar to what we see at sunset when rain is about. Lastly, when the air around the earth is thickly charged with cloud, no light at all can pass; and on such occasions the moon disappears altogether for the time being from the night sky. A total eclipse of the sun takes place when the moon comes between the sun and the earth, in such a manner that it cuts off the sunlight entirely for the time being from a portion of the earth's surface.
A person situated in the region in question will, therefore, at that moment find the sun temporarily blotted out from his view by the body of the moon. Since the moon is a very much smaller body than the sun, and also very much the nearer to us of the two, it will readily be understood that the portion of the earth from which the sun is seen thus totally eclipsed will be of small extent.
In places not very distant [Pg 66] from this region, the moon will appear so much shifted in the sky that the sun will be seen only partially eclipsed. The moon being in constant movement round the earth, the portion of the earth's surface from which an eclipse is seen as total will be always a comparatively narrow band lying roughly from west to east. This band, known as the track of totality , can, at the utmost, never be more than about miles in width, and as a rule is very much less.
For about miles on either side of it the sun is seen partially eclipsed. Outside these limits no eclipse of any kind is visible, as from such regions the moon is not seen to come in the way of the sun see Fig. It may occur to the reader that eclipses can also take place in the course of which the positions, where the eclipse would ordinarily be seen as total, will lie outside the surface of the earth. Such an eclipse is thus not dignified with the name of total eclipse, but is called a partial eclipse, because from the earth's surface the sun is only seen partly eclipsed at the utmost see Fig.
An Annular eclipse is an eclipse which just fails to become total for yet another reason.
We have pointed out that the orbits of the various members of the solar system are not circular, but oval. Such oval figures, it will be remembered, are technically known as ellipses. In an elliptic orbit the controlling body is situated not in the middle of the figure, but rather towards one of the ends; the actual point which it occupies being known as the focus.
The sun being at the focus of the earth's orbit, it follows that the earth is, at times, a little nearer to him than at others. The sun will therefore appear to us to vary a little in size, looking sometimes slightly larger than at other times. It is so, too, with the moon, at the focus of whose orbit the earth is situated. She therefore also appears to us at times to vary slightly in size. The result is that when the sun is eclipsed by the moon, and the moon at the time appears the larger of the two, she is able to blot out the sun completely, and so we can get a total eclipse.
But when, on the other hand, the sun appears the larger, the eclipse will not be quite total, for a portion of the sun's disc will be seen protruding all around the moon like a ring of light. This is what is known as [Pg 68] an annular eclipse, from the Latin word annulus , which means a ring. The term is consecrated by long usage, but it seems an unfortunate one on account of its similarity to the word "annual. There can never be a year without an eclipse of the sun. Indeed there must be always two such eclipses at least during that period, though there need be no eclipse of the moon at all.