1.
Terrestrial planet
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A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the planets are the inner planets closest to the Sun, i. e. Mercury, Venus, Earth. The terms terrestrial planet and telluric planet are derived from Latin words for Earth, as these planets are, in terms of composition, Earth-like. All terrestrial planets may have the basic type of structure, such as a central metallic core, mostly iron. The Moon is similar, but has a smaller iron core. Io and Europa are also satellites that have internal structures similar to that of terrestrial planets, terrestrial planets can have canyons, craters, mountains, volcanoes, and other surface structures, depending on the presence of water and tectonic activity. The Solar System has four planets, Mercury, Venus, Earth. Only one terrestrial planet, Earth, is known to have an active hydrosphere, during the formation of the Solar System, there were probably many more terrestrial planetesimals, but most merged with or were ejected by the four terrestrial planets. The Earths Moon has a density of 3.4 g·cm−3 and Jupiters satellites, Io,3.528 and Europa,3.013 g·cm−3, the uncompressed density of a terrestrial planet is the average density its materials would have at zero pressure. A greater uncompressed density indicates greater metal content, uncompressed density differs from the true average density because compression within planet cores increases their density, the average density depends on planet size as well as composition. The uncompressed density of terrestrial planets trends towards lower values as the distance from the Sun increases, the rocky minor planet Vesta orbiting outside of Mars is less dense than Mars still, at 3.4 g·cm−3. It is unknown whether extrasolar terrestrial planets in general will also follow this trend, most of the planets discovered outside the Solar System are giant planets, because they are more easily detectable. But since 2005, hundreds of terrestrial extrasolar planets have been found. Most of these are super-Earths, i. e. planets with masses between Earths and Neptunes, super-Earths may be gas planets or terrestrial, depending on their mass and other parameters. During the early 1990s, the first extrasolar planets were discovered orbiting the pulsar PSR B1257+12, with masses of 0.02,4.3 and it was later found to be a gas giant. In 2005, the first planets around stars that may be terrestrial were found, Gliese 876 d, has a mass 7 to 9 times that of Earth. It orbits the red dwarf Gliese 876,15 light years from Earth, oGLE-2005-BLG-390Lb, about 5.5 times the mass of Earth, orbits a star about 21,000 light years away in the constellation Scorpius. From 2007 to 2010, three potential terrestrial planets were orbiting the red dwarf Gliese 581
2.
Solar System
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The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, the heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium, it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic
3.
Mars
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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
4.
Mars trojan
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The Mars trojans are a group of objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars, the origin of the Mars trojans is not well understood. One theory suggests that they were captured in its Lagrangian points as the Solar System was forming, however, spectral studies of the Mars trojans indicate this may not be the case. One explanation for this involves asteroids wandering into the Mars Lagrangian points later in the Solar Systems formation and this is also questionable considering the very low mass of Mars
5.
Venus
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Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period of any planet in the Solar System and it is named after the Roman goddess of love and beauty. It is the second-brightest natural object in the sky after the Moon, reaching an apparent magnitude of −4.6. Because Venus orbits within Earths orbit it is a planet and never appears to venture far from the Sun. Venus is a planet and is sometimes called Earths sister planet because of their similar size, mass, proximity to the Sun. It is radically different from Earth in other respects and it has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the surface is 92 times that of Earth. Venus is by far the hottest planet in the Solar System, with a surface temperature of 735 K. Venus is shrouded by an layer of highly reflective clouds of sulfuric acid. It may have had water oceans in the past, but these would have vaporized as the temperature rose due to a greenhouse effect. The water has probably photodissociated, and the hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field. Venuss surface is a dry desertscape interspersed with rocks and is periodically resurfaced by volcanism. As one of the brightest objects in the sky, Venus has been a fixture in human culture for as long as records have existed. It has been sacred to gods of many cultures, and has been a prime inspiration for writers and poets as the morning star. Venus was the first planet to have its motions plotted across the sky, as the closest planet to Earth, Venus has been a prime target for early interplanetary exploration. It was the first planet beyond Earth visited by a spacecraft, Venuss thick clouds render observation of its surface impossible in visible light, and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991. Plans have been proposed for rovers or more missions. Venus is one of the four planets in the Solar System
6.
Mercury (planet)
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Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 88 days is the shortest of all the planets in the Solar System and it is named after the Roman deity Mercury, the messenger to the gods. Like Venus, Mercury orbits the Sun within Earths orbit as a planet, so it can only be seen visually in the morning or the evening sky. Also, like Venus and the Moon, the displays the complete range of phases as it moves around its orbit relative to Earth. Seen from Earth, this cycle of phases reoccurs approximately every 116 days, although Mercury can appear as a bright star-like object when viewed from Earth, its proximity to the Sun often makes it more difficult to see than Venus. Mercury is tidally or gravitationally locked with the Sun in a 3,2 resonance, as seen relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun. As seen from the Sun, in a frame of reference that rotates with the orbital motion, an observer on Mercury would therefore see only one day every two years. Mercurys axis has the smallest tilt of any of the Solar Systems planets, at aphelion, Mercury is about 1.5 times as far from the Sun as it is at perihelion. Mercurys surface appears heavily cratered and is similar in appearance to the Moons, the polar regions are constantly below 180 K. The planet has no natural satellites. Mercury is one of four planets in the Solar System. It is the smallest planet in the Solar System, with a radius of 2,439.7 kilometres. Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede, Mercury consists of approximately 70% metallic and 30% silicate material. Mercurys density is the second highest in the Solar System at 5.427 g/cm3, Mercurys density can be used to infer details of its inner structure. Although Earths high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller, therefore, for it to have such a high density, its core must be large and rich in iron. Geologists estimate that Mercurys core occupies about 55% of its volume, Research published in 2007 suggests that Mercury has a molten core. Surrounding the core is a 500–700 km mantle consisting of silicates, based on data from the Mariner 10 mission and Earth-based observation, Mercurys crust is estimated to be 35 km thick. One distinctive feature of Mercurys surface is the presence of narrow ridges
7.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
8.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
9.
Near-Earth object
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A near-Earth object is any small Solar System body whose orbit brings it into proximity with Earth. By definition, a solar system body is a NEO if its closest approach to the Sun is less than 1.3 astronomical unit and it is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. NEOs have become of increased interest since the 1980s because of increased awareness of the potential danger some of the asteroids or comets pose, and mitigations are being researched. In January 2016, NASA announced the Planetary Defense Coordination Office to track NEOs larger than 30 to 50 meters in diameter and coordinate an effective threat response, NEAs have orbits that lie partly between 0.983 and 1.3 AU away from the Sun. When a NEA is detected it is submitted to the IAUs Minor Planet Center for cataloging, some NEAs orbits intersect that of Earths so they pose a collision danger. The United States, European Union, and other nations are currently scanning for NEOs in an effort called Spaceguard. In the United States and since 1998, NASA has a mandate to catalogue all NEOs that are at least 1 kilometer wide. In 2006, it was estimated that 20% of the objects had not yet been found. In 2011, largely as a result of NEOWISE, it was estimated that 93% of the NEAs larger than 1 km had been found, as of 5 February 2017, there have been 875 NEAs larger than 1 km discovered, of which 157 are potentially hazardous. The inventory is much less complete for smaller objects, which still have potential for scale, though not global. Potentially hazardous objects are defined based on parameters that measure the objects potential to make threatening close approaches to the Earth. Mostly objects with an Earth minimum orbit intersection distance of 0.05 AU or less, objects that cannot approach closer to the Earth than 0.05 AU, or are smaller than about 150 m in diameter, are not considered PHOs. This makes them a target for exploration. As of 2016, three near-Earth objects have been visited by spacecraft, more recently, a typical frame of reference for looking at NEOs has been through the scientific concept of risk. In this frame, the risk that any near-Earth object poses is typically seen through a lens that is a function of both the culture and the technology of human society, NEOs have been understood differently throughout history. Each time an NEO is observed, a different risk was posed and it is not just a matter of scientific knowledge. Such perception of risk is thus a product of religious belief, philosophic principles, scientific understanding, technological capabilities, and even economical resourcefulness.03 E −0.4 megatonnes. For instance, it gives the rate for bolides of 10 megatonnes or more as 1 per thousand years, however, the authors give a rather large uncertainty, due in part to uncertainties in determining the energies of the atmospheric impacts that they used in their determination
10.
1221 Amor
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1221 Amor is the namesake of the Amor asteroids, a group of near-Earth asteroids whose orbits range between those of Earth and Mars. Amors are often Mars-crossers but they are not Earth-crossers, eugène Joseph Delporte photographed Amor as it approached Earth to within 16 million kilometers, this was the first time that an asteroid was seen to approach Earth so closely. A month later,1862 Apollo was seen to cross Earths orbit, Amor is named after the Roman god of love, better known as Cupid. See also 763 Cupido and 433 Eros, which is named after Cupids Greek counterpart, coincidentally,433 Eros, like 1221 Amor, makes close approaches to Earth. It is a Mars-crosser as well,1221 Amor at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
11.
Deimos (moon)
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Deimos is the smaller and outer of the two natural satellites of the planet Mars, the other being Phobos. Deimos has a radius of 6.2 km and takes 30.3 hours to orbit Mars. The name Deimos is pronounced /ˈdaɪmɒs/ DY-mos, /deɪmɒs/, or sometimes /ˈdiːməs/ DEE-məs or like the Greek Δεῖμος, in Greek mythology, Deimos was the twin brother of Phobos and personified terror. Deimos is 23,460 km from Mars, much further than Marss other moon, Deimos was discovered by Asaph Hall, Sr. at the United States Naval Observatory in Washington, D. C on 12 August 1877, at about 07,48 UTC. Hall also discovered Phobos on 18 August 1877, at about 09,14 GMT and it is named after Deimos, a figure representing dread in Greek Mythology. The names, at first spelled Phobus and Deimus, were suggested by Henry Madan, Science Master of Eton, from Book XV of the Iliad, where Ares summons Dread and Fear. Deimos, like Marss other moon, Phobos, has spectra, albedos, like most bodies of its size, Deimos is highly non-spherical with triaxial dimensions of 15 ×12.2 ×11 km, making it 0.56 times the size of Phobos. Deimos is composed of rich in carbonaceous material, much like C-type asteroids. It is cratered, but the surface is smoother than that of Phobos. The regolith is highly porous and has a density of only 1.471 g/cm3. It has a velocity of 5.6 m/s and an apparent magnitude of 12.45. Only two geological features on Deimos have been given names, the craters Swift and Voltaire are named after writers who speculated on the existence of two Martian moons before Phobos and Deimos were discovered. DEIMOS Deimoss orbit is circular and is close to Marss equatorial plane. Deimos is possibly an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars, though this hypothesis is still controversial and disputed. At its brightest it would be about as bright as Venus is from Earth, with a small telescope, a Martian observer could see Deimoss phases, which take 1.2648 days to run their course. Unlike Phobos, which orbits so fast that it rises in the west and sets in the east, Deimos rises in the east. Because Deimoss orbit is close to Mars and has only a very small inclination to Marss equator. Deimos regularly passes in front of the Sun as seen from Mars and it is too small to cause a total eclipse, appearing only as a small black dot moving across the Sun
12.
Phobos (moon)
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Phobos is the innermost and larger of the two natural satellites of Mars, the other being Deimos. Both moons were discovered in 1877 by American astronomer Asaph Hall, Phobos is a small, irregularly shaped object with a mean radius of 11 km, and is seven times larger than the outer moon, Deimos. Phobos is named after the Greek god Phobos, a son of Ares and Aphrodite, the name Phobos is pronounced /ˈfoʊbəs/ FOH-bəs or /ˈfoʊbɒs/ FOH-bos, or like the Greek Φόβος. Phobos orbits 6,000 km from the Martian surface, closer to its body than any other known planetary moon. It is indeed so close that it orbits Mars much faster than Mars rotates, and completes an orbit in just 7 hours and 39 minutes. As a result, from the surface of Mars it appears to rise in the west, move across the sky in 4 hours and 15 minutes or less, Phobos is one of the least reflective bodies in the Solar System, with an albedo of just 0.071. Surface temperatures range from about −4 °C on the side to −112 °C on the shadowed side. The defining surface feature is the impact crater, Stickney. Images and models indicate that Phobos may be a rubble pile held together by a thin crust, and that it is being torn apart by tidal interactions. Phobos gets closer to Mars by about 2 meters every one hundred years, Phobos was discovered by astronomer Asaph Hall on 18 August 1877, at the United States Naval Observatory in Washington, D. C. at about 09,14 Greenwich Mean Time. Hall had discovered Deimos, Mars other moon, a few days earlier on 12 August 1877 at about 07,48 UTC. The names, originally spelled Phobus and Deimus respectively, were suggested by Henry Madan, Science Master of Eton, based on Greek mythology, Phobos has dimensions of 27 ×22 ×18 km, and retains too little mass to be rounded under its own gravity. Phobos does not have a due to its low mass. It is one of the least reflective bodies in the Solar System, spectroscopically it appears to be similar to the D-type asteroids, and is apparently of composition similar to carbonaceous chondrite material. Phoboss density is too low to be rock, and it is known to have significant porosity. These results led to the suggestion that Phobos might contain a substantial reservoir of ice, spectral observations indicate that the surface regolith layer lacks hydration, but ice below the regolith is not ruled out. The most prominent of these is the crater, Stickney, an impact crater some 9 km in diameter. As with Mimass crater Herschel, the impact that created Stickney must have nearly shattered Phobos, many grooves and streaks also cover the oddly shaped surface
13.
433 Eros
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433 Eros is an S-type near-Earth asteroid approximately 34. 4×11. 2×11.2 kilometres in size, the second-largest near-Earth asteroid after 1036 Ganymed. It was discovered in 1898 and was the first near-Earth asteroid discovered and it was the first asteroid orbited by an Earth probe. It belongs to the Amor group, Eros is a Mars-crosser asteroid, the first known to come within the orbit of Mars. Objects in such an orbit can remain there for only a few hundred years before the orbit is perturbed by gravitational interactions. It is a potential Earth impactor, about five times larger than the impactor that created Chicxulub crater, the NEAR Shoemaker probe visited Eros twice, first with a 1998 flyby, and then by orbiting it in 2000 when it extensively photographed its surface. On February 12,2001, at the end of its mission, Eros was discovered on 13 August 1898 by Gustav Witt in Berlin and Auguste Charlois at Nice. Witt was taking a 2-hour exposure of Beta Aquarii to secure astrometric positions of asteroid 185 Eunike, a similar program was then carried out, during a closer approach, in 1930–1931 by Harold Spencer Jones. The value obtained by this program was considered definitive until 1968, Eros was the first asteroid detected by the Arecibo Observatorys radar system. Eros was one of the first asteroids visited by a spacecraft, the first one orbited, NASA spacecraft NEAR Shoemaker entered orbit around Eros in 2000, and landed in 2001. Eros is named after the Greek god of love, Erōs and it is pronounced /ˈɪərɒs/ EER-os or sometimes /ˈɛrɒs/ ERR-os. The rarely used form of the name is Erotian /ᵻˈroʊʃən/. Surface gravity depends on the distance from a spot on the surface to the center of a bodys mass, eross surface gravity varies greatly because Eros is not a sphere but an elongated peanut-shaped object. The daytime temperature on Eros can reach about 100 °C at perihelion, nighttime measurements fall near −150 °C. Eross density is 2.67 g/cm3, about the same as the density of Earths crust and it rotates once every 5.27 hours. NEAR scientists have found that most of the larger rocks strewn across Eros were ejected from a crater in an impact approximately 1 billion years ago. This event may also be responsible for the 40 percent of the Erotian surface that is devoid of craters smaller than 0.5 kilometers across and it was originally thought that the debris thrown up by the collision filled in the smaller craters. An analysis of crater densities over the surface indicates that the areas with lower density are within 9 kilometers of the impact point. Some of the lower density areas were found on the side of the asteroid
14.
Orbit
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In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet about a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating path around a body, to a close approximation, planets and satellites follow elliptical orbits, with the central mass being orbited at a focal point of the ellipse, as described by Keplers laws of planetary motion. For ease of calculation, in most situations orbital motion is adequately approximated by Newtonian Mechanics, historically, the apparent motions of the planets were described by European and Arabic philosophers using the idea of celestial spheres. This model posited the existence of perfect moving spheres or rings to which the stars and it assumed the heavens were fixed apart from the motion of the spheres, and was developed without any understanding of gravity. After the planets motions were accurately measured, theoretical mechanisms such as deferent. Originally geocentric it was modified by Copernicus to place the sun at the centre to help simplify the model, the model was further challenged during the 16th century, as comets were observed traversing the spheres. The basis for the understanding of orbits was first formulated by Johannes Kepler whose results are summarised in his three laws of planetary motion. Second, he found that the speed of each planet is not constant, as had previously been thought. Third, Kepler found a relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 AU distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter,5. 23/11.862, is equal to that for Venus,0. 7233/0.6152. Idealised orbits meeting these rules are known as Kepler orbits, isaac Newton demonstrated that Keplers laws were derivable from his theory of gravitation and that, in general, the orbits of bodies subject to gravity were conic sections. Newton showed that, for a pair of bodies, the sizes are in inverse proportion to their masses. Where one body is more massive than the other, it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body. Lagrange developed a new approach to Newtonian mechanics emphasizing energy more than force, in a dramatic vindication of classical mechanics, in 1846 le Verrier was able to predict the position of Neptune based on unexplained perturbations in the orbit of Uranus. This led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits, in relativity theory, orbits follow geodesic trajectories which are usually approximated very well by the Newtonian predictions but the differences are measurable. Essentially all the evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy
15.
NEAR Shoemaker
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The mission succeeded in closing in with the asteroid and orbited it several times, finally terminating by touching down on the asteroid on 12 February 2001. The primary scientific objective of NEAR was to return data on the properties, composition, mineralogy, morphology, internal mass distribution. Secondary objectives include studies of regolith properties, interactions with the wind, possible current activity as indicated by dust or gas. This data will be used to understand the characteristics of asteroids in general, their relationship to meteoroids and comets. A radio science experiment was performed using the NEAR tracking system to estimate the gravity field of the asteroid. The total mass of the instruments was 56 kg, and they required 80 W power, a previous plan for the mission was for it to go to 4660 Nereus and do a flyby of 2019 Van Albada en route. In January 2000 it would rendezvous with Nereus but instead of staying it would visit multiple asteroids, the primary goal of the mission was to study the near-Earth asteroid 433 Eros from orbit for approximately one year. Eros is an S-type asteroid approximately 13 ×13 ×33 km in size, initially the orbit was circular with a radius of 200 km. The radius of the orbit was brought down in stages to a 50 ×50 km orbit on 30 April 2000 and decreased to 35 ×35 km on July 14,2000. The orbit was raised over succeeding months to a 200 ×200 km orbit, the mission ended with a touchdown in the saddle region of Eros on February 12,2001. Some scientists claim that the goal of the mission was to link Eros. With sufficient data on chemical composition, a link could be established between Eros and other S-type asteroids, and those meteorites believed to be pieces of S-type asteroids. Once this connection is established, meteorite material can be studied with large, complex, and evolving equipment, NEAR-Shoemaker did not prove or disprove this link to the satisfaction of scientists. Between December 1999 and February 2001 NEAR Shoemaker used its gamma-ray spectrometer to detect gamma-ray bursts as part of the InterPlanetary Network, after launch on a Delta 7925-8 and exit from Earth orbit, NEAR entered the first part of its cruise phase. NEAR spent most of the phase in a minimal activity hibernation state. On 27 June 1997, NEAR flew by Mathilde within 1200 km at 12,56 UT at 9.93 km/s, returning imaging, the flyby produced over 500 images, covering 60% of Mathildes surface, as well as gravitational data allowing calculations of Mathildes dimensions and mass. On July 3,1997 NEAR executed the first major deep space maneuver and this decreased the velocity by 279 m/s and lowered perihelion from 0.99 AU to 0.95 AU. The Earth gravity assist swingby occurred on January 23,1998 at 7,23 UT
16.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
17.
Asteroid belt
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The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets, the asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, the total mass of the asteroid belt is approximately 4% that of the Moon, or 22% that of Pluto, and roughly twice that of Plutos moon Charon. Ceres, the belts only dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas. The remaining bodies range down to the size of a dust particle, the asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form a family whose members have similar orbital characteristics. Individual asteroids within the belt are categorized by their spectra. The asteroid belt formed from the solar nebula as a group of planetesimals. Planetesimals are the precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals, as a result,99. 9% of the asteroid belts original mass was lost in the first 100 million years of the Solar Systems history. Some fragments eventually found their way into the inner Solar System, Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits. Classes of small Solar System bodies in other regions are the objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids. On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are considered to sprout jets. According to one of the scientists, The lines are becoming more and more blurred between comets and asteroids. This pattern, now known as the Titius–Bode law, predicted the semi-major axes of the six planets of the provided one allowed for a gap between the orbits of Mars and Jupiter
18.
3552 Don Quixote
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3552 Don Quixote, provisionally designated 1983 SA, is a near-Earth asteroid, also classified as Amor, Mars-crossing, and Jupiter-crossing asteroid. It has a highly inclined orbit of 31 degrees that leads to frequent perturbations by Jupiter. Don Quixote measures 18.4 kilometres in diameter and has a period of 7.7 hours. It was discovered by Paul Wild at the Swiss Zimmerwald Observatory in 1983, due to its comet-like orbit and albedo, Don Quixote has ever been suspected to be an extinct comet. However, infrared observations with the Spitzer Space Telescope at 4.5 μm revealed a faint coma, the cometary activity is interpreted as CO2 molecular band emission. It is not clear if the activity is persistent or an outburst. Orbital simulation from JPL / Ephemeris 3552 Don Quixote at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
19.
Apsis
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An apsis is an extreme point in an objects orbit. The word comes via Latin from Greek and is cognate with apse, for elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- and ap-, or apo- added to a reference to the thing being orbited. For a body orbiting the Sun, the point of least distance is the perihelion, the terms become periastron and apastron when discussing orbits around other stars. For any satellite of Earth including the Moon the point of least distance is the perigee, for objects in Lunar orbit, the point of least distance is the pericynthion and the greatest distance the apocynthion. For any orbits around a center of mass, there are the terms pericenter and apocenter, periapsis and apoapsis are equivalent alternatives. A straight line connecting the pericenter and apocenter is the line of apsides and this is the major axis of the ellipse, its greatest diameter. For a two-body system the center of mass of the lies on this line at one of the two foci of the ellipse. When one body is larger than the other it may be taken to be at this focus. Historically, in systems, apsides were measured from the center of the Earth. In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body. However, in the case of spacecraft, the family of terms are used to refer to the orbital altitude of the spacecraft from the surface of the central body. The arithmetic mean of the two limiting distances is the length of the axis a. The geometric mean of the two distances is the length of the semi-minor axis b, the geometric mean of the two limiting speeds is −2 ε = μ a which is the speed of a body in a circular orbit whose radius is a. The words pericenter and apocenter are often seen, although periapsis/apoapsis are preferred in technical usage, various related terms are used for other celestial objects. The -gee, -helion and -astron and -galacticon forms are used in the astronomical literature when referring to the Earth, Sun, stars. The suffix -jove is occasionally used for Jupiter, while -saturnium has very rarely used in the last 50 years for Saturn. The -gee form is used as a generic closest approach to planet term instead of specifically applying to the Earth. During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon, regarding black holes, the term peri/apomelasma was used by physicist Geoffrey A. Landis in 1998 before peri/aponigricon appeared in the scientific literature in 2002
20.
Potentially hazardous object
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A potentially hazardous object can be known not to be a threat to Earth for the next 100 years or more, if its orbit is reasonably well determined. Potentially hazardous asteroids with some threat of impacting Earth in the next 100 years are listed on the Sentry Risk Table, as of March 2017 there are 1,786 known potentially hazardous asteroids and only 205 have an observation arc shorter than 30 days. Of the known PHAs,157 are believed to be larger than one kilometer in diameter, a calculated diameter is only a rough estimate, as it is inferred from the objects varying brightness—observed and measured at various times—and the assumed, yet unknown reflectivity of its surface. Most of the discovered PHAs are Apollo asteroids and fewer belong to the group of Aten asteroids, after several astronomical surveys, the number of known PHAs has increased tenfold since the end of the 1990s. These surveys have led to a number of 15,802 discovered near-Earth objects. Most of them are asteroids, with just some 106 near-Earth comets, the Minor Planet Centers website Unusual Minor Planets also publishes detailed statistics for these objects. This is big enough to cause devastation to human settlements unprecedented in human history in the case of a land impact. Such impact events occur on average once per 10,000 years. NEOWISE data estimates that there are 4,700 ±1,500 potentially hazardous asteroids with a greater than 100 meters. As of 2012, an estimated 20 to 30 percent of these objects have been found, Asteroids larger than 35 meters across can pose a threat to a town or city. The diameter of most small asteroids is not well determined and can only be estimated based on their brightness, for this reason NASA and the Jet Propulsion Laboratory use the more practical measure of absolute magnitude. Any asteroid with a magnitude of 22. The NASA near-Earth object program uses an assumed albedo of 0.13 for this purpose, in May 2016, the asteroid size estimates arising from the Wide-field Infrared Survey Explorer and NEOWISE missions have been questioned, but the criticism has yet to undergo peer review. Several astronomical survey projects such as Lincoln Near-Earth Asteroid Research and Catalina Sky Survey continue to search for more PHOs, both professional and amateur astronomers participate in such monitoring. This is a reflection of the character of the Solar System. The two main scales used to categorize the impact hazards of asteroids are the Palermo Technical Impact Hazard Scale, the lowest numbered PHA is 1566 Icarus. The largest known Potentially hazardous asteroid is 1999 JM8 with a diameter of ~7 km, below is listed the largest PHA discovered in a given year. Historical data of the number of discovered PHA since 1999 are displayed in the bar charts—one for the total number
21.
Aten asteroid
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The Aten asteroids are a group of asteroids, whose orbit brings them into proximity with Earth. The group is named after 2062 Aten, the first of its kind, since then, more than 1,000 Atens have been discovered, of which many are classified as potentially hazardous asteroids. For a list of existing articles, see Aten asteroids and List of Aten asteroids, Aten asteroids are defined by having a semi-major axis of less than one astronomical unit, the average distance from the Earth to the Sun. They also have a greater than 0.983 AU. Asteroids orbits can be highly eccentric, an Aten orbit need not be entirely contained within Earths orbit, as nearly all known Aten asteroids have their aphelion greater than 1 AU although their semi-major axis is less than 1 AU. Observation of objects inferior to the Earths orbit is difficult and this difficulty may be the cause of some sampling bias in the apparent preponderance of eccentric Atens, Aten asteroids account for only about 6% of the known near-Earth asteroid population. Many more Apollo-class asteroids are known than Aten-class asteroids, possibly because of the sampling bias, the shortest semi-major axis for any known Aten asteroid is 2008 EY5 at 0.626 AU. A very small possibility of impact remained for 2036, but this was also eliminated, there are also sixteen known Apohele asteroids, traditionally listed as a subclass of Atens, but generally regarded a separate class of their own. Unlike Atens, Apoheles permanently stay within Earths orbit and do not cross it
22.
Apollo asteroid
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The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth crossing asteroids that have an orbital semi-major axis greater than that of the Earth, as of November 2016, the steadily growing number of known Apollo asteroids has reached a total of 8,180 members. It is by far the largest group of objects, compared to the Aten, Amor. Currently, there are 1,133 numbered Apollos, asteroids are not numbered until they have been observed at two or more oppositions. There are also 1,472 Apollo asteroids that are enough. The closer their semi-major axis is to Earths, the eccentricity is needed for the orbits to cross. The largest known Apollo asteroid is 1866 Sisyphus, with a diameter of about 8.5 km, examples of known Apollo asteroids include, Apollo asteroids Apollo asteroid records List of Apollo minor planets
23.
Hans-Emil Schuster
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Hans-Emil Schuster is a German astronomer and a discoverer of minor planets and comets, who retired in October 1991. He worked at Hamburg Observatory at Bergedorf and European Southern Observatory, since 1982, he was married to Rosemarie Schuster née von Holt He discovered periodic comet 106P/Schuster. He also discovered the comet C/1976 D2, which was notable for its large perihelion distance of 6.88 AU and he discovered 25 asteroids, including notably the Apollo asteroid 2329 Orthos and the Amor asteroids 2608 Seneca,3271 Ul,3288 Seleucus, and 3908 Nyx. He discovered the near-Earth asteroid 161989 Cacus, which was lost, Schuster participated in the exploration, selection and testing of the sites of two ESO observatories, La Silla Observatory and Paranal Observatory. He also participated in two ESO Southern Sky Surveys, the ESO-B survey completed in 1978 was the first deep optical survey of the sky. Photographic plates were taken with the ESOs 1-meter Schmidt Telescope at La Silla and he co-discovered the Phoenix Dwarf galaxy, and in 1976 also discovered the Eridanus Globular Cluster, one of the most distant globular clusters in the galactic halo. In 1980, he discovered a supernova in the galaxy NGC1255. However, Schusters Spiral is not named him, but a different Schuster. The asteroid 2018 Schuster was named in his honour, on 21 October 2011 he was awarded the rank of Commander of the Order of Bernardo OHiggins in recognition of his important contribution to astronomy in Chile. List of minor planet discoverers § Discovering astronomers The ESO/Uppsala Survey of the ESO Atlas 106P/Schuster, cometography. com Phoenix Dwarf, Spiders Homepage
24.
Max Wolf
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Maximilian Franz Joseph Cornelius Max Wolf was a German astronomer and a pioneer in the field of astrophotography. He was Chairman of Astronomy at the University of Heidelberg and director of the Heidelberg-Königstuhl State Observatory from 1902 until his death and he was born in Heidelberg, Germany on June 21,1863, the son of a popular medical doctor, Dr. Franz Wolf. His father encouraged an interest in science and built an observatory for his son in the garden of the family home and it is from here that Wolf is credited with his first astronomical discovery, comet 14P/Wolf, in 1884. He attended the world famous university and, in 1888, at the age of 25. He spent one year of study in Stockholm, the only significant time he would spend outside of Heidelberg in his life. He returned to the University of Heidelberg and accepted the position of privat-docent in 1890, a popular lecturer in astronomy, he declined offers of positions from other institutions. In 1902 he was appointed Chair of Astronomy and Director of the new Landessternwarte Heidelberg-Königstuhl observatory, positions he would hold until his death in 1932. While the new observatory was being built Wolf was appointed to supervise the construction and he proved to be a not only a capable supervisor but also a successful money raiser. Wolf immediately designed and ordered a double refractor telescope from American astronomer and instrument builder and this instrument, known as the Bruce double-astrograph, with parallel 16 in lenses and a fast f/5 focal ratio, became the observatorys primary research telescope. He also raised money for a 28 in reflector telescope, the first for the observatory, in 1910 Wolf proposed to the Carl Zeiss optics firm the creation of a new instrument, now known as the planetarium. World War I intervened before this could be developed, but the Carl Zeiss company resumed this project after peace was restored, the first official public showing was at the Deutsches Museum in Munich, Germany on October 21,1923. During his trip to America he was interested in learning more about the new field of astrophotography. The two would become lifelong correspondents, competitors, collaborators and friends, Wolf was clearly moved by the death of his friend in 1923 and wrote a long obituary. The University, already world-renowned in many fields, became well known for astronomy. Wolf himself was a researcher, contributing numerous papers in many areas of astronomy up to the end of his life. Like his friend, E. E. Barnard, he died rather young for an astronomer and he died in Heidelberg on October 3,1932, at the age of 69. He was survived by his widow and three sons, Wolf started his career as a comet hunter and continued to discover them throughout his life. He discovered or co-discovered several comets, including 14P/Wolf and 43P/Wolf-Harrington and he won a competition with E. E. Barnard on who would be the first to observe the return of Halleys Comet in April,1910
25.
Johann Palisa
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Johann Palisa was an Austrian astronomer, born in Troppau in Austrian Silesia. He was a discoverer of asteroids, discovering 122 in all. Some of his discoveries include 153 Hilda,216 Kleopatra,243 Ida,253 Mathilde,324 Bamberga. He was awarded the Valz Prize from the French Academy of Sciences in 1906, the Phocaea main-belt asteroid 914 Palisana, discovered by Max Wolf in 1919, and the lunar crater Palisa were named in his honour. From 1866 to 1870, Palisa studied mathematics and astronomy at the University of Vienna, however, despite this, by 1870 he was an assistant at the Universitys observatory, and a year later gained a position at the observatory in Geneva. A few years later, in 1872, at the age of 24, while at Pula, he discovered his first asteroid,136 Austria, on March 18,1874. Along with this, he discovered twenty-seven minor planets and one comet, during his stay in Pula he used a small six-inch refractor telescope to aid in his research. Between 1874 and 1923 Palisa discovered 122 asteroids ranging from 136 Austria to 1073 Gellivara and he worked from Pola and Vienna. He also discovered the parabolic comet C/1879 Q1 in the year 1879, one of his discoveries was 253 Mathilde, which was visited by the spacecraft NEAR Shoemaker on June 27,1997. The robotic probe passed within 1200 km of Mathilde at 12,56 UT at 9.93 km/s, returning imaging and other instrument data including over 500 images which covered 60% of Mathildes surface. Portraits of Johann Palisa from the Lick Observatory Records Digital Archive, UC Santa Cruz Librarys Digital Collections von Hepperger, J. Anzeige des Todes von Johann Palisa
26.
1580 Betulia
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1580 Betulia is an Amor asteroid discovered on May 22,1950, by Ernest Leonard Johnson at the Union Observatory, Johannesburg, South Africa. Betulias shape has been determined, at its widest point. The name honours Betulia Toro, wife of the astronomer Samuel Herrick, Herrick had studied the asteroids orbit, and requested the name, along with that of 1685 Toro. Harris, Alan W. Mueller, Michael, Delbó, Marco, Busc, the surface properties of small asteroids, Peculiar Betulia - A case study. Lebofsky, L. A. Veeder, G. J. Lebofsky, M. J. Matson, visual and radiometric photometry of 1580 Betulia. IAUC1268 - Initial discovery JPL Small-Body Database Browser on 1580 Betulia 1580 Betulia at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
27.
1627 Ivar
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1627 Ivar, provisional designation 1929 SH, is a stony asteroid and near-Earth object of the Amor group, approximately 9 kilometers in diameter. It was discovered on 25 September 1929, by Danish astronomer Ejnar Hertzsprung at Leiden Southern Station, the S-type asteroid orbits the Sun at a distance of 1. 1–2.6 AU once every 2 years and 6 months. Its orbit has an eccentricity of 0.40 and an inclination of 8° with respect to the ecliptic, ivars observation arc begins with its official discovery observation in 1929, as no precoveries were taken, and no prior identifications were made. It has an Earth minimum orbit intersection distance of 0.1124 AU, the eccentric Amor asteroid is also a Mars-crosser. In 2074, it will pass Earth at 0.141 AU, a large number of rotational light-curves of Ivar have been obtained from photometric observations since 1985. They give a rotation period between 4.795 and 4.80 hours with a brightness variation between 0.27 and 1.16 magnitude, indicative of its non-spheroidal shape. Future photometric observations will show whether the YORP effect will slowly change the spin rate. In 1985, the body was observed with radar from the Arecibo Observatory in Puerto Rico at a distance of 0.20 AU. The measured radar cross-section was 7.5 square kilometers.37 and 10.2 kilometers in diameter, the Collaborative Asteroid Lightcurve Link adopts an albedo of 0.151 and a diameter of 9.12 kilometers with an absolute magnitude of 12.87. This minor planet was named by the discoverer in honor of his late brother Ivar Hertzsprung, naming citation was published before November 1977
28.
1980 Tezcatlipoca
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1980 Tezcatlipoca, provisional designation 1950 LA, is an eccentric, stony asteroid, classified as a near-Earth object of the Amor group of asteroids, approximately 6 kilometers in diameter. It was discovered on 19 June 1950, by American astronomer Albert G. Wilson and it was named after the Aztech deity Tezcatlipoca. Tezcatlipoca orbits the Sun at a distance of 1. 1–2.3 AU once every 2 years and 3 months and its orbit has an eccentricity of 0.36 and an inclination of 27° with respect to the ecliptic. Its Earth minimum orbit intersection distance is less than 0.246 AU. The S-type asteroid is classified as a Sw-type by the ExploreNEOs project, the Collaborative Asteroid Lightcurve Link agrees with the revised NEOWISE observations, that is, an albedo of 0.128 and a diameter of 6.0 kilometers with an absolute magnitude of 13.96. This minor planet was named after Tezcatlipoca, the Aztech deity of matter and his animal counterpart was the jaguar and his contender was Quetzálcoatl, after which the minor planet 1915 Quetzálcoatl is named. Both deities are Aztec creator gods and were depicted as twin serpents that coil round each other to produce time, naming citation was published before November 1977
