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.
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
5.
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
6.
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
7.
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
8.
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
9.
1862 Apollo
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1862 Apollo /əˈpɒloʊ/ is a stony asteroid, approximately 1.5 kilometers in diameter, classified as a near-Earth object. It was discovered by German astronomer Karl Reinmuth at Heidelberg Observatory on 24 April 1932, in addition, since Apollos orbit is highly eccentric, it crosses the orbits of Venus and Mars and is therefore called a Venus-crosser and Mars-crosser as well. The analysis of its rotation provided observational evidence of the YORP effect and it is named after the Greek god Apollo. He is the god of the Sun, child of Zeus and Leto, after which the minor planets 5731 Zeus and 68 Leto are named. On November 4,2005, it was announced that a moon, or satellite of Apollo, had been detected by radar observations from Arecibo Observatory, Puerto Rico. The standard provisional designation for this satellite is S/20051, the announcement is contained in the International Astronomical Union Circular 8627. The satellite is only 80 m across and orbits Apollo just 3 km away from the asteroid itself, from the surface of Apollo, S/20051 would have an angular diameter of about 2.0835 degrees. 1862 Apollo is a potentially hazardous asteroid because its minimum orbit intersection distance is less than 0.05 AU, Apollos Earth MOID is 0.0257 AU. Its orbit is well-determined for the several hundred years. On 17 May 2075 it will pass 0.0083 AU from Venus, lost asteroid Lightcurve plot of 1862 Apollo, Palmer Divide Observatory, B. D. Warner Asteroids with Satellites, Robert Johnston, johnstonsarchive
10.
Earth-crosser asteroid
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An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earths orbit. The known numbered Earth-crossers are listed here and those Earth-crossers whose semi-major axes are smaller than Earths are Aten asteroids, the remaining ones are Apollo asteroids. An asteroid with an Earth-crossing orbit is not necessarily in danger of colliding with Earth, the orbit of an Earth-crossing asteroid may not even intersect with that of Earth. This apparent contradiction arises because many asteroids have highly inclined orbits, so although they may have a less than that of Earth. An asteroid for which there is possibility of a collision with Earth at a future date. Specifically, an asteroid is a PHA if its Earth minimum orbital intersection distance is <0.05 AU, the concept of PHA is intended to replace the now abandoned strict definition of ECA which existed for a few years. Having a small MOID is not a guarantee of a collision, on the other hand, small gravitational perturbations of the asteroid around its orbit from planets that it passes can significantly alter its path. For instance,99942 Apophis will approach Earth so closely in 2029 that it will get under the orbit of the Earths geostationary satellites, the Earth will change the trajectory of Apophis and the result may be an even closer approach in the future, possibly 2036. Of the Earth-crossing asteroids,3753 Cruithne is notable for having an orbit that has the period as Earths.2 AU
11.
Semi-major and semi-minor axes
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In geometry, the major axis of an ellipse is its longest diameter, a line segment that runs through the center and both foci, with ends at the widest points of the perimeter. The semi-major axis is one half of the axis, and thus runs from the centre, through a focus. Essentially, it is the radius of an orbit at the two most distant points. For the special case of a circle, the axis is the radius. One can think of the axis as an ellipses long radius. The semi-major axis of a hyperbola is, depending on the convention, thus it is the distance from the center to either vertex of the hyperbola. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction. Thus a and b tend to infinity, a faster than b, the semi-minor axis is a line segment associated with most conic sections that is at right angles with the semi-major axis and has one end at the center of the conic section. It is one of the axes of symmetry for the curve, in an ellipse, the one, in a hyperbola. The semi-major axis is the value of the maximum and minimum distances r max and r min of the ellipse from a focus — that is. In astronomy these extreme points are called apsis, the semi-minor axis of an ellipse is the geometric mean of these distances, b = r max r min. The eccentricity of an ellipse is defined as e =1 − b 2 a 2 so r min = a, r max = a. Now consider the equation in polar coordinates, with one focus at the origin, the mean value of r = ℓ / and r = ℓ /, for θ = π and θ =0 is a = ℓ1 − e 2. In an ellipse, the axis is the geometric mean of the distance from the center to either focus. The semi-minor axis of an ellipse runs from the center of the ellipse to the edge of the ellipse, the semi-minor axis is half of the minor axis. The minor axis is the longest line segment perpendicular to the axis that connects two points on the ellipses edge. The semi-minor axis b is related to the axis a through the eccentricity e. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction
12.
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
13.
Perihelion and aphelion
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The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory
14.
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
15.
Amor asteroid
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The Amor asteroids are a group of near-Earth asteroids named after the asteroid 1221 Amor. They approach the orbit of Earth from beyond, but do not cross it, most Amors cross the orbit of Mars. The two moons of Mars, Deimos and Phobos, may be Amor asteroids that were captured by Marss gravity, the most famous member of this group is 433 Eros, which was the first asteroid to be orbited and then landed upon by a human probe. There are three general criteria which an asteroid must meet to be considered a member of the Amor asteroid class, to be considered near, the asteroid must come closer to Earth than to any other major planet. The closest planet to Earth is Venus, which can come as close as 0.27 AU, therefore, an Amor asteroid must come within 0.30 AU of Earths orbit. The asteroids orbit must be outside the orbit of Earth, asteroids that come close to Earth whose orbits are inside Earths orbit are considered Apohele asteroids. The asteroids orbit must not cross Earths orbit, the most commonly used definition of this is that it never orbits closer to the Sun than Earths average distance from the Sun. A more strict definition is that at any point along the asteroids orbit and this takes into consideration the fact that Earths orbit ranges between 0.983 and 1.016 AU from the Sun. It is more difficult to sort out the Amor asteroids from the non-Amor asteroids using this definition, however. These three criteria boil down to a single test for membership, If an asteroid has a perihelion between 1.000 AU and 1.300 AU, it is an Amor asteroid. Any asteroid with this trait is considered an Amor-class asteroid, regardless of its axis, eccentricity, aphelion, inclination, physical properties, orbital stability. An asteroid belongs to the Amor group if, Its orbital period is greater than one year and this is equivalent to saying that its semi-major axis is greater than 1.0 AU. Its orbit does not cross Earths orbit and that is, its lowest point is higher than Earths highest point. It is an object, that is, its perihelion distance q <1.3 AU. In summary, a >1.0 AU and 1.017 AU < q <1.3 AU, there are 6051 Amor asteroids currently known. 960 of them are numbered, and 73 of them are named, Amor asteroids can be partitioned into four subgroups, depending on their average distance from the Sun. The Amor I subgroup consists of Amor asteroids whose semi-major axes are in between Earth and Mars and that is, they have a semi-major axis between 1.000 and 1.523 AU. Less than one fifth of Amor asteroids belong to this subgroup, Amor I asteroids have lower eccentricities than the other subgroups of Amors
16.
Opposition (planets)
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In positional astronomy, two celestial bodies are said to be in opposition when they are on opposite sides of the sky, viewed from a given place. A planet is said to be in opposition when it is in opposition to the Sun, opposition occurs only in superior planets. The instant of opposition is defined as that when the apparent geocentric longitude of the body differs by 180° from the apparent geocentric longitude of the Sun. When it is in opposition, a lunar eclipse occurs. The astronomical symbol for opposition is ☍, handwritten, As seen from a planet that is superior, an inferior planet on the opposite side of the Sun is in superior conjunction with the Sun. An inferior conjunction occurs when the two lie in a line on the same side of the Sun. At inferior conjunction, the planet is in opposition to the Sun as seen from the inferior planet. Conjunction Positional astronomy Syzygy Asteroids around opposition – British Astronomical Association - Computing Section
17.
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
18.
Orbital eccentricity
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The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is an orbit, values between 0 and 1 form an elliptical orbit,1 is a parabolic escape orbit. The term derives its name from the parameters of conic sections and it is normally used for the isolated two-body problem, but extensions exist for objects following a rosette orbit through the galaxy. In a two-body problem with inverse-square-law force, every orbit is a Kepler orbit, the eccentricity of this Kepler orbit is a non-negative number that defines its shape. The limit case between an ellipse and a hyperbola, when e equals 1, is parabola, radial trajectories are classified as elliptic, parabolic, or hyperbolic based on the energy of the orbit, not the eccentricity. Radial orbits have zero angular momentum and hence eccentricity equal to one, keeping the energy constant and reducing the angular momentum, elliptic, parabolic, and hyperbolic orbits each tend to the corresponding type of radial trajectory while e tends to 1. For a repulsive force only the trajectory, including the radial version, is applicable. For elliptical orbits, a simple proof shows that arcsin yields the projection angle of a circle to an ellipse of eccentricity e. For example, to view the eccentricity of the planet Mercury, next, tilt any circular object by that angle and the apparent ellipse projected to your eye will be of that same eccentricity. From Medieval Latin eccentricus, derived from Greek ἔκκεντρος ekkentros out of the center, from ἐκ- ek-, eccentric first appeared in English in 1551, with the definition a circle in which the earth, sun. Five years later, in 1556, a form of the word was added. The eccentricity of an orbit can be calculated from the state vectors as the magnitude of the eccentricity vector, e = | e | where. For elliptical orbits it can also be calculated from the periapsis and apoapsis since rp = a and ra = a, where a is the semimajor axis. E = r a − r p r a + r p =1 −2 r a r p +1 where, rp is the radius at periapsis. For Earths annual orbit path, ra/rp ratio = longest_radius / shortest_radius ≈1.034 relative to center point of path, the eccentricity of the Earths orbit is currently about 0.0167, the Earths orbit is nearly circular. Venus and Neptune have even lower eccentricity, over hundreds of thousands of years, the eccentricity of the Earths orbit varies from nearly 0.0034 to almost 0.058 as a result of gravitational attractions among the planets. The table lists the values for all planets and dwarf planets, Mercury has the greatest orbital eccentricity of any planet in the Solar System. Such eccentricity is sufficient for Mercury to receive twice as much solar irradiation at perihelion compared to aphelion, before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit
19.
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
20.
Chelyabinsk meteor
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It quickly became a brilliant superbolide meteor over the southern Ural region. The light from the meteor was brighter than the Sun, visible up to 100 km away and it was observed over a wide area of the region and in neighbouring republics. Some eyewitnesses also felt intense heat from the fireball, on account of its high velocity and shallow angle of atmospheric entry, the object exploded in an air burst over Chelyabinsk Oblast, at a height of around 29.7 km. The explosion generated a bright flash, producing a hot cloud of dust and gas that penetrated to 26.2 km, the object was undetected before its atmospheric entry, in part because its radiant was close to the Sun. Its explosion created panic among residents, and about 1,500 people were injured seriously enough to seek medical treatment. Some 7,200 buildings in six cities across the region were damaged by the shock wave. The Chelyabinsk meteor is also the only confirmed to have resulted in a large number of injuries. Amateur videos showed a fireball streaking across the sky and a loud boom several minutes afterwards, some eyewitnesses also felt intense heat from the fireball. The event began at 09,20,21 Yekaterinburg time, several minutes after sunrise in Chelyabinsk, according to eyewitnesses, the bolide appeared brighter than the sun, as was later confirmed by NASA. An image of the object was taken shortly after it entered the atmosphere by the weather satellite Meteosat 9. Witnesses in Chelyabinsk said that the air of the city smelled like gunpowder, sulfur and burning odors starting about 1 hour after the fireball, the visible phenomenon due to the passage of an asteroid or meteoroid through the atmosphere is called a meteor. If the object reaches the ground, then it is called a meteorite, during the Chelyabinsk meteoroids traversal, there was a bright object trailing smoke, then an air burst that caused a powerful blast wave. The latter was the cause of the damage to thousands of buildings in Chelyabinsk. The fragments then entered dark flight and created a field of numerous meteorites on the snow-covered ground. The last time a similar phenomenon was observed in the Chelyabinsk region was the Kunashak meteor shower of 1949, preliminary estimates released by the Russian Federal Space Agency indicated the object was an asteroid moving at about 30 km/s in a low trajectory when it entered Earths atmosphere. According to the Russian Academy of Sciences, the meteor then pushed through the atmosphere at a velocity of 15 km/s, the radiant appears from video recordings to have been above and to the left of the rising Sun. On 1 March 2013 NASA published a synopsis of the event, stating that at peak brightness. The air bursts blast wave, when it hit the ground, the Russian Geographical Society said the passing of the meteor over Chelyabinsk caused three blasts of different energy
21.
Chelyabinsk
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During Pugachevs Rebellion, the fortress withstood a siege by the rebel forces in 1774, but was eventually captured for several months in 1775. In 1782, as a part of Ufa Viceroyalty that was reformed into Orenburg Governorate, Chelyabinsk became a seat of a its own uyezd and finally was granted town status. Until the late 19th century, Chelyabinsk was a provincial town. In 1892, the Samara-Zlatoust Railway was completed which connected it with Moscow, also in 1892, construction of the Trans-Siberian Railway from Chelyabinsk started and in 1896 the city was linked to Ekaterinburg. Chelyabinsk became the hub for relocation to Siberia, for fifteen years more than fifteen million people - a tenth of Russia - passed through Chelyabinsk. Some of them remained in Chelyabinsk, which contributed to its rapid growth, soon Chelyabinsk started turning into a major trade center, its population reached 20,000 inhabitants by 1897,45,000 by 1913, and 70,000 by 1917. For rapid growth at the turn of the 20th century, similar to American cities, during the first Five-Year Plans of the 1930s, Chelyabinsk experienced rapid industrial growth. Several establishments, including the Chelyabinsk Tractor Plant and the Chelyabinsk Metallurgical Plant, were built at this time, during World War II, Joseph Stalin decided to move a large part of Soviet factory production to places out of the way of the advancing German armies in late 1941. This brought new industries and thousands of workers to Chelyabinsk, facilities for the production of T-34 tanks and Katyusha rocket launchers existed in Chelyabinsk. During World War II, it produced 18,000 tanks, in the press of the time Chelyabinsk was informally called Tankograd or Tank City. Kirov Factory no.185 moved here from Leningrad to produce heavy tanks, fragments fell in and around Chelyabinsk. Interior Ministry spokesman Vadim Kolesnikov said 1,100 people had called for medical assistance following the incident, one woman suffered a broken spine. Kolesnikov also said about 600 square meters of a roof at a factory had collapsed. The size has been estimated at 17 meters diameter with a mass of 10,000 or 11,000 metric tons, the power of the explosion was about 500 kilotons of TNT, which is 20–30 times more energy than was released from the atomic bomb exploded in Hiroshima. Luckily, thanks to the altitude of the explosion the city managed to avoid large casualties. Chelyabinsk is the center of the oblast. Within the framework of administrative divisions, it is incorporated as the City of Chelyabinsk—an administrative unit with the equal to that of the districts. As a municipal division, the City of Chelyabinsk is incorporated as Chelyabinsky Urban Okrug, in June 2014, Chelyabinsks seven city districts were granted municipal status
22.
Wide-field Infrared Survey Explorer
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Wide-field Infrared Survey Explorer is a NASA infrared-wavelength astronomical space telescope launched in December 2009, and placed in hibernation in February 2011 when its transmitter turned off. WISE discovered thousands of planets and numerous star clusters. Its observations also supported the discovery of the first Y Dwarf, WISE performed an all-sky astronomical survey with images in 3.4,4.6,12 and 22 μm wavelength range bands, over ten months using a 40 cm diameter infrared telescope in Earth orbit. After its hydrogen coolant depleted, a mission extension called NEOWISE was conducted to search for near-Earth objects such as comets. The All-Sky data including processed images, source catalogs and raw data, was released to the public on March 14,2012, in August 2013, NASA announced it would reactivate the WISE telescope for a new three-year mission to search for asteroids that could collide with Earth. Science operations and data processing for WISE and NEOWISE take place at the Infrared Processing, the mission was planned to create infrared images of 99 percent of the sky, with at least eight images made of each position on the sky in order to increase accuracy. The spacecraft was placed in a 525 km, circular, polar, Sun-synchronous orbit for its mission, during which it has taken 1.5 million images. Each image covers a 47-arcminute field of view, which means a 6-arcsecond resolution, each area of the sky was scanned at least 10 times at the equator, the poles were scanned at theoretically every revolution due to the overlapping of the images. The produced image library contains data on the local Solar System, the Milky Way, among the objects WISE studied are asteroids, cool, dim stars such as brown dwarfs, and the most luminous infrared galaxies. Stellar nurseries, which are covered by interstellar dust, are detectable in infrared, Infrared measurements from the WISE astronomical survey have been particularly effective at unveiling previously undiscovered star clusters. Examples of such embedded star clusters are Camargo 18, Camargo 440, Majaess 101, in addition, galaxies of the young Universe and interacting galaxies, where star formation is intensive, are bright in infrared. On this wavelength the interstellar gas clouds are also detectable, as well as proto-planetary discs, WISE satellite was expected to find at least 1,000 of those proto-planetary discs. WISE was not able to detect Kuiper belt objects, because their temperatures are too low and it was able to detect any objects warmer than 70–100 K. A Neptune-sized object would be out to 700 AU, a Jupiter-mass object out to 1 light year. A larger object of 2–3 Jupiter masses would be visible at a distance of up to 7–10 light years and that translates to about 1000 new main-belt asteroids per day, and 1–3 NEOs per day. The peak of magnitude distribution for NEOs will be about 21–22 V, WISE would detect each typical Solar System object 10–12 times over about 36 hours in intervals of 3 hours. Construction of the WISE telescope was divided between Ball Aerospace & Technologies, SSG Precision Optronics, Inc, DRS and Rockwell, Lockheed Martin, and Space Dynamics Laboratory. The program was managed through the Jet Propulsion Laboratory, the WISE instrument was built by the Space Dynamics Laboratory in Logan, Utah
23.
2011 MD
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2011 MD is an Apollo asteroid that passed relatively close to Earths surface — at a distance of about 12,000 kilometers, roughly the diameter of the Earth — at around 17,00 UTC on June 27,2011. Although the object was believed to be space junk, subsequent observations confirmed that it is an asteroid. A few hours before the asteroids nearest approach in 2011, it appeared close to the Sun, backyard astronomers were able to observe it with telescopes from Australia, southern Africa, and the Americas. However, according to the more recent absolute magnitude measurement of 28.1 and its albedo of 0.3, the June 27,2011 close approach to Earth increased the orbital period of 2011 MD from 380 days to 396 days. During close approach the asteroid passed Earth at a speed of 6.7 km/s with a geocentric eccentricity of 1.1. 2011 MD was observed by the Spitzer Space Telescope in February 2014, the asteroid is a porous rubble pile with a density similar to water. On June 19,2014, NASA reported that asteroid 2011 MD was a candidate for capture by the Asteroid Redirect Mission in the early 2020s. Asteroid capture Asteroid Redirect Mission Near-Earth Object Encounter animations 2011 MD at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
24.
2010 AL30
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2010 AL30 is a near-Earth asteroid that was discovered on 10 January 2010. Italian scientists Ernesto Guido and Giovanni Sostero told RIA Novosti that it had a period of almost exactly one year. However, it was determined that it is a near-Earth asteroid, on January 13,2010 at 1246 UT it passed Earth at 0.0008624 AU, about 1/3 of the distance from the Earth to the Moon. Based an estimated diameter of 10–15 m, if 2010 AL30 had entered the Earths atmosphere, the Nagasaki Fat Man atom bomb had a yield between 13–18 kT. It has an uncertainty parameter of 2 and has been observed by radar, radar observations show the asteroid is elongated and is about 30 meters in diameter. It may be a contact binary
25.
2009 WM1
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2009 WM1 is an Apollo near-Earth asteroid that is estimated to be 280 metres in diameter with an estimated mass of 2. 9×1010 kg. When the asteroid was first discovered for about a month it was listed at a Torino Scale of 1. It was removed from the Sentry Risk Table on 26 June 2013,2009 WM1 will pass 0.0046 AU from Earth on 2059-Nov-23. Even though 2009 WM1 has an Earth MOID of 0.00009 AU, the orbit and future close approaches are well determined with an orbital uncertainty of 1. 2009 WM1 will pass Earth at a distance of 0.0005 AU to 0. 069AU on 2199-Nov-23, but since it is a close approach, the 21 May 2014 Earth close approach of 0.3622 AU should allow a refinement to the orbit. From 7 May 2014 until 2 June 2014 the asteroid will be brighter than apparent magnitude 20, the asteroid will come to opposition on 18 May 2014 when it will be up all night. Orbital simulation from JPL / Horizons Ephemeris 2009 WM1 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
26.
2008 TC3
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2008 TC3 was an 80 metric tons,4.1 meters diameter asteroid that entered Earths atmosphere on October 7,2008. It exploded at an estimated 37 kilometers above the Nubian Desert in Sudan, some 600 meteorites, weighing a total of 10.5 kilograms, were recovered, many of these belonged to a rare type known as ureilites, which contain, among other minerals, nanodiamonds. It was the first time that an impact had been predicted prior to its entry into the atmosphere as a meteor. The asteroid was discovered by Richard A. Kowalski at the Catalina Sky Survey 1. 5-meter telescope at Mount Lemmon, north of Tucson, Arizona, US and it was notable as the first such body to be observed and tracked prior to reaching Earth. The process of detecting and tracking an object, an effort sometimes referred to as Spaceguard, was put to the test. On October 7,01,49 UTC, the asteroid entered the shadow of the Earth, Impact predictions were performed by University of Pisas CLOMON2 semi-automatic monitoring system as well as Jet Propulsion Laboratorys Sentry system. Spectral observations that were performed by astronomers at the 4. 2-meter William Herschel Telescope at La Palma, Canary Islands are consistent with either a C-type or M-type asteroid. It exploded tens of kilometers above the ground with the energy of 0.9 to 2.1 kilotons of TNT over an area of the Nubian Desert. The Times reported that the light was so intense that it lit up the sky like a full moon. A webcam captured the flash lighting up El-Gouna beach 725 kilometres north of the explosion, a low-resolution image of the explosion was captured by the weather satellite Meteosat 8. The Meteosat images place the fireball at 21. 00°N32. 15°E /21.00,32. 15. Infrasound detector arrays in Kenya also detected a sound wave from the direction of the expected impact corresponding to energy of 1.1 to 2.1 kilotons of TNT, asteroids of this size hit Earth about two or three times a year. These images have not been publicly released, EUMETSAT fireball images A search of the impact zone that began on December 6,2008, turned up 10.5 kilograms of rock in some 600 fragments. These meteorites are collectively named Almahata Sitta, which means Station Six in Arabic and is a station between Wadi Halfa and Khartoum, Sudan. The initial 15 meteorites were found in the first three days of the search, numerous witnesses were interviewed, and the hunt was guided with a search grid and specific target area produced by NASAs Jet Propulsion Laboratory in Pasadena, California. The first sample measured was an anomalous ultra-fine-grained porous polymict ureilite achondrite, reflectance spectra of the meteorite, combined with the astronomical observations, identified asteroid 2008 TC3 as an F-type asteroid class. These fragile anomalous dark carbon-rich ureilites are now linked to the group of F-class asteroids. Amino acids have been found on the meteorite, carbonaceous chondrites List of notable asteroids 1972 Great Daylight Fireball Impact event 2014 AA WT1190F Atkinson, N
27.
2007 VK184
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2007 VK184 is an Apollo near-Earth asteroid estimated to be about 130 meters in diameter. It was listed on the Sentry Risk Table with a Torino Scale rating of 1, a Torino scale rating of 1 is a routine discovery in which a pass near the Earth is predicted that poses no unusual level of danger. 2007 VK184 was discovered on November 12,2007, by the Catalina Sky Survey and it was recovered on March 26,2014 by Mauna Kea, and removed from the Sentry Risk Table on March 28,2014. By January 4,2008, with an arc of 52 days. The Sentry Risk Table, using an arc of 60 days. Since the March 2014 recovery, it is known that the asteroid will pass 0.013 AU from Earth on June 2,2048. Before the 2014 close approach, the asteroid had a modest observation arc of 60 days, on May 23,2014, the asteroid passed 0.17 AU from Earth and reached an apparent magnitude of ~20.8. As expected the close approach allowed astronomers to recover the asteroid on March 26,2014, as the asteroid gets closer to Earth, the positional uncertainty becomes larger. By recovering the asteroid well before closest approach you can avoid searching a region of the sky. Most asteroids rated 1 on the Torino Scale are later downgraded to 0 after more observations come in, Risk assessments were calculated based on a diameter of 130 meters. It was estimated that, if it were ever to impact Earth, it would enter the atmosphere at a speed of 19.2 km/s and would have a kinetic energy equivalent to 150 megatons of TNT. Assuming the target surface is sedimentary rock, the asteroid would impact the ground with the equivalent of 40 megatons of TNT, Asteroids of approximately 130 meters in diameter are expected to impact Earth once every 11000 years or so. On March 26–27,2014, additional observations were made which ruled out the chance of an impact in 2048,99942 Apophis, a NEO that, for a few days, was thought to have a slight probability of striking the Earth in 2029. But the likelihood that would happen was quickly determined to be zero,2007 VK184 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters Orbital simulation from JPL / Ephemeris List Of The Potentially Hazardous Asteroids
28.
2007 TU24
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2007 TU24 is an Apollo near-Earth asteroid that was discovered by the Catalina Sky Survey in Arizona on October 11,2007. Imaging radar has estimated that it is 250 meters in diameter, the asteroid passed 554,209 kilometer from Earth on January 29,2008, at 08,33 UTC. At closest approach the asteroid had an apparent magnitude of 10.3 and was about 50 times fainter than the eye can see. It required about a 3-inch telescope to be seen, from the date of discovery of asteroid 2007 TU24 on 11 October 2007, a total of 316 observations of it had been made by 31 January 2008, spanning 112 days. Now the asteroid has an arc of about 3 years. It was removed from the Sentry Risk Table on 4 December 2007 at 14,05 UTC, goldstone Observatory carried out radar observations on January 23 and January 24,2008. As of January 24, the orbit of the asteroid was known with such a precision that scientists were able to calculate close approaches from the year 67 AD to 2141 AD. On January 29,2008 at 08,33 UTC,2007 TU24 passed by the earth at a distance of 0.0037043 AU with a relative speed of 9.248 km/s. Observations from Arecibo Observatory were taken on February 1–4 and it is a contact binary asteroid. Asteroid 2004 XP14 was the closest potentially hazardous asteroid, passing Earth by 432,308 km,0.00289 AU, asteroid 4179 Toutatis came within 1.5 million km,0.0104 AU of the Earth on September 29,2004. On August 7,2027,1999 AN10 will pass within 388,960 km of the Earth
29.
2007 WD5
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2007 WD5 is an Apollo asteroid some 50 m in diameter and a Mars-crosser asteroid first observed on November 20,2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD5 caused excitement amongst the community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on January 30,2008. However, by January 9,2008, additional observations allowed NASAs Near Earth Object Program to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact,2007 WD5 most likely passed Mars at a distance of 6.5 Mars radii. The asteroid was discovered on November 20,2007 by Andrea Boattini of the NASA-funded Catalina Sky Survey on Mount Lemmon, near Tucson, Arizona, United States and it was discovered in the constellation Taurus at an apparent magnitude of +20. This is about 400,000 times fainter than most people can see with the eye on a dark night far from city lights. It was discovered nineteen days after passing near the Earth, by the time it arrived at Mars it had an apparent magnitude of roughly +26 and therefore appeared over 100x fainter than at the time of discovery. November 1,2007, Nineteen days before its discovery, this small asteroid passed within 7.5 million km of the Earth, November 20,2007, The asteroid was first discovered by Andrea Boattini of the Catalina Sky Survey. December 21,2007,2007 WD5 was approximately halfway between Earth and Mars traveling at 27,900 mph and it was estimated by NASAs Near Earth Object Program to have a 1-in-75 chance of colliding with Mars on January 30,2008 at approximately 10,55 UT. It was thought it would pass about 50,000 km from Mars, December 28,2007, NASA scientists at the Near-Earth Object program office at JPL announced they had found 2007 WD5 in 3 precovery images from November 8,2007. The refined orbit placed the odds of a Mars impact at 1-in-25, the uncertainty region was reduced from 1 million km to roughly 400,000 km. The best fit trajectory had the asteroid passing within 21,000 km of Mars, the pre-discovery observations were located by Andy Puckett in the archive of the Sloan Digital Sky Survey II at the Apache Point Observatory. The uncertainty region was reduced to roughly 200,000 km and still intersected Mars, the uncertainty region was reduced by a factor of 3. January 9,2008, Following several new observations, NASA reduced the uncertainty region, the chance of collision became only 1-in-10,000. The best estimate was that around 12,00 UTC the asteroid passed about 26,000 km from the planets center, analyses show there is no possibility of an impact with either Mars or Earth in the next century. This trend of increasing probability of impact followed by a decrease is typical as uncertainties are gradually reduced. In December 2004, a trend was observed with 99942 Apophis where the predicted probability of impact with Earth in 2029 at one point reached as high as 2. 7%. If the asteroid had collided with Mars, it would have hit with a velocity of about 13.5 km/s, and would have produced an explosion equivalent to about 3 megatons of TNT. Due to the atmosphere of Mars, it was predicted that the asteroid would have reached the surface intact
30.
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
31.
(308635) 2005 YU55
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2005 YU55, provisionally known as 2005 YU55, is a potentially hazardous asteroid 360±40 meters in diameter, as measured after its Earth flyby. Previously it was estimated at 310 meters or about 400 m in diameter and it was discovered on 28 December 2005 by Robert S. McMillan at Steward Observatory, Kitt Peak. On 8 November 2011 it passed 0.85 lunar distances from Earth, in February 2010,2005 YU55 was rated 1 on the Torino Scale for a potential pass near Earth on November 10,2103, that posed no unusual level of danger. On 19 April 2010, radar ranging by the Arecibo radio telescope reduced uncertainties about the orbit by 50% and this improvement eliminated any possibility of an impact with Earth within the next 100 years. It was removed from the Sentry Risk Table on 22 April 2010 and it is now known that on 10 November 21032005 YU55 will be roughly 2 AU from Earth. On 8 November 2011 at 23,28 UT the asteroid passed 0.85 LD from Earth, on 9 November 2011 at 07,13 UT the asteroid passed 0.6231 LD from the Moon. Since the gibbous moon did interfere with the viewing, observers trying to locate the asteroid required a telescope with an aperture of 6 inches or larger. According to Jay Melosh, if an asteroid the size of 2005 YU55 were to hit land, it would create a crater 6.3 km across,518 m deep and generate a seven-magnitude-equivalent-earthquake. The chances of a collision with an asteroid like 2005 YU55 is about 1 percent in the next thousand years. During the 2011 passage 2005 YU55 was studied with radar using Goldstone, Arecibo, the Very Long Baseline Array, the Herschel Space Observatory has made far-infrared measurements of 2005 YU55 on November 10, helping determine its temperature and composition. Radar analysis has helped to pin down the asteroids albedo. Although radar measurements do not detect visible light they can determine the distance and this information, coupled with visible light measurements, provides a more accurate measure of an objects absolute magnitude, and therefore its albedo. On November 8,2011, NASA released a statement mentioning a number of structures on the surface of the asteroid, on November 11,2011, higher-resolution images showed concavities, a ridge near the asteroids equator, and numerous features interpreted as decameter-scale boulders. Shape modeling based on the radar images shows that YU55s shape is close to spheroidal, with dimensions of 360±40 m. Optical lightcurve measurements during the flyby provided an accurate estimate of the asteroids spin period – about 19.3 hours. Because 2005 YU55 is so nearly spheroidal, it was not significantly torqued by Earths tides during the flyby, optical, near-infrared, and ultraviolet spectroscopy confirmed that 2005 YU55 is a C-type asteroid. On 19 January 2029,2005 YU55 will pass 0.0023 AU from Venus, the close approach distance to Venus in 2029 will determine how close the asteroid will pass to Earth in 2041. Before the November 2011 observations, the uncertainties in the post-2029 trajectory showed that the asteroid would pass somewhere between 0.002 AU and 0.3 AU of Earth in 2041, radar astrometry in November 2011 clarified the Earth passage in 2041 and beyond
32.
Lowell Observatory Near-Earth-Object Search
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Lowell Observatory Near-Earth-Object Search was a project designed to discover asteroids and comets that orbit near the Earth. The project, funded by NASA, was directed by Dr. Ted Bowell of Lowell Observatory in Flagstaff, the LONEOS project began in 1993 and ran until the end of February 2008. LONEOS, in its configuration, used a 0. 6-meter f/1.8 Schmidt telescope, acquired from Ohio Wesleyan University in 1990. This combination of instruments provided a field of view of 2.88 by 2.88 degrees and it had a maximum nightly scan area of about 1,000 square degrees. The instrument could cover the entire accessible dark sky in about a month, the CCD has detected asteroids as faint as visual magnitude 19.8 but its typical limiting visual magnitude was 19.3. The instrument is located at Lowell Observatorys dark sky site, Anderson Mesa Station, near Flagstaff, Arizona, two were used for frame reductions, one for telescope pointing control and one for camera control. The camera control software had scripting capability and could control all the other computers, asteroids were found by obtaining four pictures of the same region of sky, each frame temporally separated by 15 to 30 minutes. The set of four frames were then submitted to reduction software which located all star-like sources on the frame, the observer visually examined all asteroid detections that had motion different from a typical main-belt asteroid. Human examination was required because most putative NEO detections were not real, all asteroid positions were converted to equatorial coordinates. Various USNO star catalogs were used for this conversion until 2007, then the Sloan Digital Sky Survey catalog was used, along with supplemental information from the Carlsberg Catalog and the 2MASS catalog. Asteroid brightness was converted to standard visual magnitude and these data, along with the time of the observations, were sent to the Minor Planet Center from which they were distributed to the scientific community. Potential near-Earth objects were handled expeditiously so that other observers could locate the asteroid on the same night, telescope operation was automated to the extent that the survey could be run all night without observer intervention. However, the telescope was operated in the automatic mode because an observer was required to reduce data promptly. During the period of LONEOS operation, several other NASA funded NEO searches were underway and these projects include LINEAR, CSS, Spacewatch, and NEAT. Amateur observers made a significant contribution during this time with independent NEO discoveries, the table below lists the number of discoveries made by LONEOS each year of operation. Asteroids thought to be larger than one kilometer in diameter were used as benchmarks in assessing survey completeness, hence, some table elements have two numbers separated by a slash. The second number represents the number of larger than one kilometer. The column labeled Asteroid Observations is the number of sent to the MPC
