An impact crater is an circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity impact of a smaller body. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters range from small, bowl-shaped depressions to large, multi-ringed impact basins. Meteor Crater is a well-known example of a small impact crater on Earth. Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Callisto and most small moons and asteroids. On other planets and moons that experience more active surface geological processes, such as Earth, Mars, Europa, Io and Titan, visible impact craters are less common because they become eroded, buried or transformed by tectonics over time. Where such processes have destroyed most of the original crater topography, the terms impact structure or astrobleme are more used.
In early literature, before the significance of impact cratering was recognised, the terms cryptoexplosion or cryptovolcanic structure were used to describe what are now recognised as impact-related features on Earth. The cratering records of old surfaces, such as Mercury, the Moon, the southern highlands of Mars, record a period of intense early bombardment in the inner Solar System around 3.9 billion years ago. The rate of crater production on Earth has since been lower, but it is appreciable nonetheless; this indicates that there should be far more young craters on the planet than have been discovered so far. The cratering rate in the inner solar system fluctuates as a consequence of collisions in the asteroid belt that create a family of fragments that are sent cascading into the inner solar system. Formed in a collision 160 million years ago, the Baptistina family of asteroids is thought to have caused a large spike in the impact rate causing the Chicxulub impact that may have triggered the extinction of the non-avian dinosaurs 66 million years ago.
Note that the rate of impact cratering in the outer Solar System could be different from the inner Solar System. Although Earth's active surface processes destroy the impact record, about 190 terrestrial impact craters have been identified; these range in diameter from a few tens of meters up to about 300 km, they range in age from recent times to more than two billion years, though most are less than 500 million years old because geological processes tend to obliterate older craters. They are selectively found in the stable interior regions of continents. Few undersea craters have been discovered because of the difficulty of surveying the sea floor, the rapid rate of change of the ocean bottom, the subduction of the ocean floor into Earth's interior by processes of plate tectonics. Impact craters are not to be confused with landforms that may appear similar, including calderas, glacial cirques, ring dikes, salt domes, others. Daniel M. Barringer, a mining engineer, was convinced that the crater he owned, Meteor Crater, was of cosmic origin.
Yet, most geologists at the time assumed. In the 1920s, the American geologist Walter H. Bucher studied a number of sites now recognized as impact craters in the United States, he concluded they had been created by some great explosive event, but believed that this force was volcanic in origin. However, in 1936, the geologists John D. Boon and Claude C. Albritton Jr. revisited Bucher's studies and concluded that the craters that he studied were formed by impacts. Grove Karl Gilbert suggested in 1893. Ralph Baldwin in 1949 wrote that the Moon's craters were of impact origin. Around 1960, Gene Shoemaker revived the idea. According to David H. Levy, Gene "saw the craters on the Moon as logical impact sites that were formed not in eons, but explosively, in seconds." For his Ph. D. degree at Princeton, under the guidance of Harry Hammond Hess, Shoemaker studied the impact dynamics of Barringer Meteor Crater. Shoemaker noted Meteor Crater had the same form and structure as two explosion craters created from atomic bomb tests at the Nevada Test Site, notably Jangle U in 1951 and Teapot Ess in 1955.
In 1960, Edward C. T. Chao and Shoemaker identified at Meteor Crater, proving the crater was formed from an impact generating high temperatures and pressures, they followed this discovery with the identification of coesite within suevite at Nördlinger Ries, proving its impact origin. Armed with the knowledge of shock-metamorphic features, Carlyle S. Beals and colleagues at the Dominion Astrophysical Observatory in Victoria, British Columbia and Wolf von Engelhardt of the University of Tübingen in Germany began a methodical search for impact craters. By 1970, they had tentatively identified more than 50. Although their work was controversial, the American Apollo Moon landings, which were in progress at the time, provided supportive evidence by recognizing the rate of impact cratering on the Moon; because the processes of erosion on the Moon are minimal, craters persist. Since the Earth could be expected to have the same cratering rate as the Moon, it became clear that the Earth had suffered far more impacts than could be seen by counting evident craters.
Impact cratering invo
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, the natural hazards that threaten it; the organization has four major science disciplines, concerning biology, geography and hydrology. The USGS is a fact-finding research organization with no regulatory responsibility; the USGS is a bureau of the United States Department of the Interior. The USGS employs 8,670 people and is headquartered in Reston, Virginia; the USGS has major offices near Lakewood, Colorado, at the Denver Federal Center, Menlo Park, California. The current motto of the USGS, in use since August 1997, is "science for a changing world." The agency's previous slogan, adopted on the occasion of its hundredth anniversary, was "Earth Science in the Public Service." Since 2012, the USGS science focus is directed at six topical "Mission Areas", namely Climate and Land Use Change, Core Science Systems, Ecosystems and Minerals and Environmental Health, Natural Hazards, Water.
In December 2012, the USGS split the Energy and Minerals and Environmental Health Mission Area resulting in seven topical Mission Areas, with the two new areas being: Energy and Minerals and Environmental Health. Administratively, it is divided into six Regional Units. Other specific programs include: Earthquake Hazards Program monitors earthquake activity worldwide; the National Earthquake Information Center in Golden, Colorado on the campus of the Colorado School of Mines detects the location and magnitude of global earthquakes. The USGS runs or supports several regional monitoring networks in the United States under the umbrella of the Advanced National Seismic System; the USGS informs authorities, emergency responders, the media, the public, both domestic and worldwide, about significant earthquakes. It maintains long-term archives of earthquake data for scientific and engineering research, it conducts and supports research on long-term seismic hazards. USGS has released the UCERF California earthquake forecast.
As of 2005, the agency is working to create a National Volcano Early Warning System by improving the instrumentation monitoring the 169 volcanoes in U. S. territory and by establishing methods for measuring the relative threats posed at each site. The USGS National Geomagnetism Program monitors the magnetic field at magnetic observatories and distributes magnetometer data in real time; the USGS collaborates with Canadian and Mexican government scientists, along with the Commission for Environmental Cooperation, to produce the North American Environmental Atlas, used to depict and track environmental issues for a continental perspective. The USGS operates the streamgaging network for the United States, with over 7400 streamgages. Real-time streamflow data are available online. National Climate Change and Wildlife Science Center implements partner-driven science to improve understanding of past and present land use change, develops relevant climate and land use forecasts, identifies lands and communities that are most vulnerable to adverse impacts of change from the local to global scale.
Since 1962, the Astrogeology Research Program has been involved in global and planetary exploration and mapping. In collaboration with Stanford University, the USGS operates the USGS-Stanford Ion Microprobe Laboratory, a world-class analytical facility for U--Pb geochronology and trace element analyses of minerals and other earth materials. USGS operates a number of water related programs, notably the National Streamflow Information Program and National Water-Quality Assessment Program. USGS Water data is publicly available from their National Water Information System database; the USGS operates the National Wildlife Health Center, whose mission is "to serve the nation and its natural resources by providing sound science and technical support, to disseminate information to promote science-based decisions affecting wildlife and ecosystem health. The NWHC provides information, technical assistance, research and leadership on national and international wildlife health issues." It is the agency responsible for surveillance of H5N1 avian influenza outbreaks in the United States.
The USGS runs 17 biological research centers in the United States, including the Patuxent Wildlife Research Center. The USGS is investigating collaboration with the social networking site Twitter to allow for more rapid construction of ShakeMaps; the USGS produces several national series of topographic maps which vary in scale and extent, with some wide gaps in coverage, notably the complete absence of 1:50,000 scale topographic maps or their equivalent. The largest and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle, a non-metric scale unique to the United States. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart. Nearly 57,000 individual maps in this series cover the 48 contiguous states, Hawaii, U. S. territories, areas of Alaska near Anchorage and Prudhoe Bay. The area covered by each map varies with the latitude of its represented location due to convergence of the meridians. At lower latitudes, near 30° north, a 7.5-minute quadrangle contains an area of about 64 square miles.
At 49° north latitude, 49 square miles are contained within a quadrangle of that size. As a unique non-metric map scale, the 1:24,000 scale requires a separate and specialized romer scale for pl
Cambridge University Press
Cambridge University Press is the publishing business of the University of Cambridge. Granted letters patent by King Henry VIII in 1534, it is the world's oldest publishing house and the second-largest university press in the world, it holds letters patent as the Queen's Printer. The press mission is "to further the University's mission by disseminating knowledge in the pursuit of education and research at the highest international levels of excellence". Cambridge University Press is a department of the University of Cambridge and is both an academic and educational publisher. With a global sales presence, publishing hubs, offices in more than 40 countries, it publishes over 50,000 titles by authors from over 100 countries, its publishing includes academic journals, reference works and English language teaching and learning publications. Cambridge University Press is a charitable enterprise that transfers part of its annual surplus back to the university. Cambridge University Press is both the oldest publishing house in the world and the oldest university press.
It originated from letters patent granted to the University of Cambridge by Henry VIII in 1534, has been producing books continuously since the first University Press book was printed. Cambridge is one of the two privileged presses. Authors published by Cambridge have included John Milton, William Harvey, Isaac Newton, Bertrand Russell, Stephen Hawking. University printing began in Cambridge when the first practising University Printer, Thomas Thomas, set up a printing house on the site of what became the Senate House lawn – a few yards from where the press's bookshop now stands. In those days, the Stationers' Company in London jealously guarded its monopoly of printing, which explains the delay between the date of the university's letters patent and the printing of the first book. In 1591, Thomas's successor, John Legate, printed the first Cambridge Bible, an octavo edition of the popular Geneva Bible; the London Stationers objected strenuously. The university's response was to point out the provision in its charter to print "all manner of books".
Thus began the press's tradition of publishing the Bible, a tradition that has endured for over four centuries, beginning with the Geneva Bible, continuing with the Authorized Version, the Revised Version, the New English Bible and the Revised English Bible. The restrictions and compromises forced upon Cambridge by the dispute with the London Stationers did not come to an end until the scholar Richard Bentley was given the power to set up a'new-style press' in 1696. In July 1697 the Duke of Somerset made a loan of £200 to the university "towards the printing house and presse" and James Halman, Registrary of the University, lent £100 for the same purpose, it was in Bentley's time, in 1698, that a body of senior scholars was appointed to be responsible to the university for the press's affairs. The Press Syndicate's publishing committee still meets and its role still includes the review and approval of the press's planned output. John Baskerville became University Printer in the mid-eighteenth century.
Baskerville's concern was the production of the finest possible books using his own type-design and printing techniques. Baskerville wrote, "The importance of the work demands all my attention. Caxton would have found nothing to surprise him if he had walked into the press's printing house in the eighteenth century: all the type was still being set by hand. A technological breakthrough was badly needed, it came when Lord Stanhope perfected the making of stereotype plates; this involved making a mould of the whole surface of a page of type and casting plates from that mould. The press was the first to use this technique, in 1805 produced the technically successful and much-reprinted Cambridge Stereotype Bible. By the 1850s the press was using steam-powered machine presses, employing two to three hundred people, occupying several buildings in the Silver Street and Mill Lane area, including the one that the press still occupies, the Pitt Building, built for the press and in honour of William Pitt the Younger.
Under the stewardship of C. J. Clay, University Printer from 1854 to 1882, the press increased the size and scale of its academic and educational publishing operation. An important factor in this increase was the inauguration of its list of schoolbooks. During Clay's administration, the press undertook a sizeable co-publishing venture with Oxford: the Revised Version of the Bible, begun in 1870 and completed in 1885, it was in this period as well that the Syndics of the press turned down what became the Oxford English Dictionary—a proposal for, brought to Cambridge by James Murray before he turned to Oxford. The appointment of R. T. Wright as Secretary of the Press Syndicate in 1892 marked the beginning of the press's development as a modern publishing business with a defined editorial policy and administrative structure, it was Wright who devised the plan for one of the most distinctive Cambridge contributions to publishing—the Cambridge Histories. The Cambridge Modern History was published
Far side of the Moon
The far side of the Moon is the hemisphere of the Moon that always faces away from Earth. The far side's terrain is rugged with a multitude of impact craters and few flat lunar maria, it has one of the largest craters in the South Pole -- Aitken basin. Both sides of the Moon experience two weeks of sunlight followed by two weeks of night. About 18 percent of the far side is visible from Earth due to libration; the remaining 82 percent remained unobserved until 1959, when it was photographed by the Soviet Luna 3 space probe. The Soviet Academy of Sciences published the first atlas of the far side in 1960; the Apollo 8 astronauts were the first humans to see the far side with the naked eye when they orbited the Moon in 1968. All manned and unmanned soft landings had taken place on the near side of the Moon, until 3 January 2019 when the Chang'e 4 spacecraft made the first landing on the far side. Astronomers have suggested installing a large radio telescope on the far side, where the Moon would shield it from possible radio interference from Earth.
Tidal forces from Earth have slowed down the Moon's rotation to the point where the same side is always facing the Earth—a phenomenon called tidal locking. The other face, most of, never visible from the Earth, is therefore called the "far side of the Moon". Over time, some parts of the far side can be seen due to libration. In total, 59 percent of the Moon's surface is visible from Earth at another. Useful observation of the parts of the far side of the Moon visible from Earth is difficult because of the low viewing angle from Earth; the phrase "dark side of the Moon" does not refer to "dark" as in the absence of light, but rather "dark" as in unknown: until humans were able to send spacecraft around the Moon, this area had never been seen. While many misconstrue this to think that the "dark side" receives little to no sunlight, in reality, both the near and far sides receive equal amounts of light directly from the Sun. However, the near side receives sunlight reflected from the Earth, known as earthshine.
Earthshine does not reach the area of the far side. Only during a full Moon is the whole far side of the Moon dark; the word "dark" has expanded to refer to the fact that communication with spacecraft can be blocked while the spacecraft is on the far side of the Moon, during Apollo space missions for example. The two hemispheres of the Moon have distinctly different appearances, with the near side covered in multiple, large maria; the far side has a battered, densely cratered appearance with few maria. Only 1 % of the surface of the far side is covered compared to 31.2 % on the near side. One accepted explanation for this difference is related to a higher concentration of heat-producing elements on the near-side hemisphere, as has been demonstrated by geochemical maps obtained from the Lunar Prospector gamma-ray spectrometer. While other factors, such as surface elevation and crustal thickness, could affect where basalts erupt, these do not explain why the far side South Pole–Aitken basin was not as volcanically active as Oceanus Procellarum on the near side.
It has been proposed that the differences between the two hemispheres may have been caused by a collision with a smaller companion moon that originated from the Theia collision. In this model, the impact led to an accretionary pile rather than a crater, contributing a hemispheric layer of extent and thickness that may be consistent with the dimensions of the far side highlands; the far side has more visible craters. This was thought to be a result of the effects of lunar lava flows, which cover and obscure craters, rather than a shielding effect from the Earth. NASA calculates that the Earth obscures only about 4 square degrees out of 41,000 square degrees of the sky as seen from the Moon. "This makes the Earth negligible as a shield for the Moon it is that each side of the Moon has received equal numbers of impacts, but the resurfacing by lava results in fewer craters visible on the near side than the far side though both sides have received the same number of impacts."Newer research suggests that heat from Earth at the time when the Moon was formed is the reason the near side has fewer impact craters.
The lunar crust consists of plagioclases formed when aluminium and calcium condensed and combined with silicates in the mantle. The cooler, far side experienced condensation of these elements sooner and so formed a thicker crust; until the late 1950s, little was known about the far side of the Moon. Librations of the Moon periodically allowed limited glimpses of features near the lunar limb on the far side, but only up to 59% of the total surface of the moon; these features, were seen from a low angle, hindering useful observation. The remaining 82% of the surface on the far side remained unknown, its properties were subject to much speculation. An example of a far side feature that can be seen through libration is the Mare Orientale, a prominent impact basin spanning 1,000 km, yet this was not named as a feature until 1906, by Julius Franz in Der Mond; the true natur
Joliot is a large lunar impact crater that lies on the far side of the Moon, just past the eastern limb. At this location it lies in a region of the surface that comes into sight during a favorable libration, although at such times it is viewed from the side, thus viewing this crater in detail must be done from orbit. The crater lies at the northern fringes of the lava-flooded region of the surface associated with Mare Marginis to the south; the crater Lomonosov is located just to the east-northeast, Lyapunov is attached to the western rim. Attached to the northwest rim, thus adjacent to Lyapunov, is the crater Rayleigh. Southwest of Joliet farther to the south lies Al-Biruni; the outer rim of Joliet is worn and somewhat disintegrated in the northern and southern sections where the outer wall consists of little more than irregular ridges and craterlets. The rim is somewhat more intact to the east, so in the west where it has been buttressed by adjacent crater formations. Within the outer rim, the interior floor has been flooded in the past by basaltic lava, leaving a flattened surface that has a lower albedo than the surrounding terrain and so appears darker.
Parts of the floor have been coated in ray material from the fresh crater Giordano Bruno to the northeast. The lava-covered floor contains several ghost-crater remnants, with the largest being an elongated formation to the west of the midpoint. At the midpoint of the floor is a central peak formation. By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint, closest to Joliot
Ewen Adair Whitaker was a British-born astronomer who specialized in lunar studies. During World War II he was engaged in quality control for the lead sheathing of hollow cables strung under the English Channel as part of the "Pipe Line Under The Ocean" Project to supply gasoline to Allied military vehicles in France. After the war, he obtained a position at the Royal Greenwich Observatory working on the UV spectra of stars, but became interested in lunar studies; as a sideline, Whitaker drew and published the first accurate chart of the South Polar area of the Moon in 1954, served as director of the Lunar Section of the British Astronomical Association. After meeting Dr. Gerard P. Kuiper, Director of Yerkes Observatory in Wisconsin, USA, at an International Astronomical Union meeting in Dublin in 1955, he was invited to join Kuiper's fledgling Lunar Project at Yerkes to work on producing a high-quality photographic atlas of the Moon; the dawn of the Space Age with the launch of the Russian Sputnik 1 soon put the Lunar Project in NASA's limelight.
In 1960, Whitaker followed Kuiper to the University of Arizona where the small Lunar Project evolved into the Lunar and Planetary Laboratory with over 300 scientists and supporting staff. The resulting Photographic Lunar Atlas, Orthographic Atlas of the Moon, the Rectified Lunar Atlas proved to be invaluable for the planning and operational stages of spacecraft missions to the Moon. Whitaker was involved with several NASA missions, including locating the landing site of Surveyor 3; this was used to set the landing site for the Apollo 12 mission whose astronauts visited the Surveyor lander. Whitaker was considered by some to be the world's leading expert on lunar nomenclature, he was active in the IAU's Task Group for Lunar Nomenclature, in 1999 he published a book on the history of lunar mapping and nomenclature, titled "Mapping and Naming the Moon." Whitaker retired from the LPL in 1978. He remained in Tucson, until his death on 11 October 2016. Co-investigator with G. P. Kuiper, H. Urey, G. Shoemaker, R. Heacock, on Lunar Ranger Project.
Member of Lunar Surveyor TV Investigator Team. Member of Lunar Orbiter 5 Scientific Site Selection Team. Member of Apollo Orbital Science Photo Team. First to apply the Zwicky technique of differential UV/Red photography to the Moon, which maps areas of differing chemical composition of the lunar surface, his results were used in Apollo site choices. Discovery and approximate determination of the orbital eccentricity and inclination of Miranda, Uranus's 5th satellite, made possible by a simple plate-measuring method that he devised and which gave a tenfold increase in precision. With colleague D. W. Arthur, added about 60 new names to anonymous craters near the limb of the Moon, brought into prominence in the Rectified Atlas, he chose 14 favorably located farside craters to commemorate the Challenger and Columbia astronauts who lost their lives in the two disasters. Determined with considerable confidence the dates on which Galileo made his drawings of the Moon and composed the various relevant sections of his "Sidereus Nuncius."
Devised a logical lettering system for designating unnamed craters on the Moon's farside. Long after his retirement, made contributions to the history of the telescope, constructing an instrument built to a 16th-century design attributed to Leonard Digges capable of producing magnified wide-field images. Over 130 atlases, papers, reviews, chapters for books, etc. A selection of the more important given below. Photographic Lunar Atlas, ed. G. P. Kuiper, with 3 others Orthographic Atlas of the Moon, ed. G. P. Kuiper with 1 other Rectified Lunar Atlas, with 3 others Consolidated Lunar Atlas, with 4 others Location of the Surveyor Spacecraft An Investigation of the Lunar Heiligenschein Mare Imbrium Lava Flows and their Relationship to Color Boundaries Artificial Lunar Impact Craters. Walter Goodacre Medal recipient and Prize from Britis