1.
4179 Toutatis
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With its close approaches, and being about 4.6 km across, it is listed as a potentially hazardous object, although the probability of a collision with Earth is minute. On December 12,2012 at 06,40 UT Toutatis passed within about 18 lunar distances of Earth. On December 13, the Chinese lunar probe Change 2, launched in 2010 on a mission, flew by Toutatis at a distance of 3.2 kilometers. Toutatis approached Earth again in 2016, but will not make another close approach until 2069. 4179 Toutatis was first sighted on February 10,1934, as object 1934 CT and it remained a lost asteroid for several decades until it was rediscovered on January 4,1989, by Christian Pollas, and was named after the Celtic god of tribal protection Toutatis. The spectral properties suggest that this is an S-type, or stony asteroid and it has a moderate Bond albedo of 0.13. Radar imagery shows that Toutatis is an irregular body consisting of two distinct lobes, with maximum widths of about 4.6 km and 2.4 km respectively. It is hypothesized that Toutatis formed from two separate bodies which coalesced at some point, with the resultant asteroid being compared to a rubble pile. It has a period around its long axis of 5.38 days. This long axis is precessing with a period of 7.38 days, the asteroid may have lost most of its original angular momentum and entered into this tumbling motion as a result of the YORP effect. With a semimajor axis of 2.5294 AU, or roughly 2.5 times the distance between Earth and the Sun, Toutatis has a 3,1 orbital resonance with Jupiter and a near-1,4 resonance with Earth. It thus completes one orbit around the Sun for every 4.02 annual orbits of Earth, estimates in 1993 put the Lyapunov time horizon for predictability at around 50 years, after which the uncertainty region becomes larger with each close approach to a planet. Without the perturbations from the planets the Lyapunov time would be close to 10,000 years. The initial observations that showed its chaotic behavior were made by Wiśniewski, the low inclination of the orbit allows frequent transits, where the inner planets Mercury, Venus, Earth, and Mars can appear to cross the Sun as seen from the perspective of Toutatis. Earth did this in January 2009, July 2012 and July 2016, Toutatis makes frequent close approaches to Earth, with a currently minimum possible distance of just 0.006 AU. The approach on September 29,2004, was close, at 0.0104 AU from Earth, presenting a good opportunity for observation. A close approach of 0.0502 AU happened on November 9,2008, the most recent close approach was on December 12,2012, at a distance of 0.046 AU, with a magnitude of 10.7. At magnitude 10.7, Toutatis was not visible to the naked eye, during the 2012 encounter Toutatis was recovered on May 21,2012, by the Siding Spring Survey at apparent magnitude 18.9
2.
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
3.
Asteroid
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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers
4.
Radar astronomy
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Radar astronomy is a technique of observing nearby astronomical objects by reflecting microwaves off target objects and analyzing the reflections. This research has been conducted for six decades, Radar astronomy differs from radio astronomy in that the latter is a passive observation and the former an active one. Radar systems have used for a wide range of solar system studies. The radar transmission may either be pulsed or continuous, the strength of the radar return signal is proportional to the inverse fourth-power of the distance. Upgraded facilities, increased power, and improved apparatus have increased observational opportunities. Radar techniques provide information unavailable by other means, such as testing general relativity by observing Mercury, Radar images provide information about the shapes and surface properties of solid bodies, which cannot be obtained by other ground-based techniques. Relying upon high powered terrestrial radars radar astronomy is able to provide extremely accurate astrometric information on the structure, composition and this aids in forming long-term predictions of asteroid-Earth impacts, as illustrated by the object 99942 Apophis. In particular, optical observations measure where an object appears in the sky, Radar, on the other hand, directly measures the distance to the object. The combination of optical and radar observations normally allows the prediction of orbits at least decades, there are two radar astronomy facilities that are in regular use, the Arecibo Planetary Radar and the Goldstone Solar System Radar. Control of attributes of the signal Resolve objects spatially, Delay-Doppler measurement precision, Optically opaque penetration, the maximum range of astronomy by radar is very limited, and is confined to the Solar system. This is because the signal drops off very steeply with distance to the target, the small fraction of incident flux that is reflected by the target. The distance to which the radar can detect an object is proportional to the root of the objects size. Radar could detect something ~1 km across a large fraction of an AU away, but at 8-10 AU and it is also necessary to have a relatively good ephemeris of the target before observing it. The Moon is comparatively close and was detected by radar soon after the invention of the technique in 1946, measurements included surface roughness and later mapping of shadowed regions near the poles. The next easiest target is Venus, in addition such technical prowess had great public relations value, and was an excellent demonstration to funding agencies. This led to early claims which are now known to be incorrect, all of these agreed with each other and the conventional value of AU at the time. The first un-ambiguous detection of Venus was made by Jet Propulsion Laboratory on 10 March 1961, a correct measurement of the AU soon followed. Once the correct value was known, other groups found echos in their archived data that agreed with these results, the following is a list of planetary bodies that have been observed by this means, Mars - Mapping of surface roughness from Arecibo Observatory
5.
Goldstone Deep Space Communications Complex
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The Goldstone Deep Space Communications Complex, commonly called the Goldstone Observatory, is located in the Mojave Desert near Barstow in the U. S. state of California. Operated by the US National Aeronautics and Space Administrations Jet Propulsion Laboratory, its purpose is to track. It is named after Goldstone, California, a nearby gold-mining ghost town, the complex includes the Pioneer Deep Space Station, which is a U. S. National Historic Landmark. The current communications complex is one of three in the NASA Deep Space Network, the others being the Madrid Deep Space Communications Complex and the Canberra Deep Space Communication Complex. Five large parabolic antennas are located at the Goldstone site to handle the workload, the antennas function similarly to a home satellite dish. The radio frequencies used for communication are in the microwave part of the radio spectrum, S band, X band. In addition to receiving radio signals from the spacecraft, the antennas transmit commands to the spacecraft with high power radio transmitters powered by klystron tubes. A major goal in the design of the station is to reduce interference with the weak incoming downlink radio signals by natural, the remote Mojave Desert location was chosen because it is far from manmade sources of radio noise such as motor vehicles. The RF front ends of the receivers at the dishes use ruby masers. It is commonly believed that the first American satellite, Explorer 1, was confirmed to be in orbit by the use of the phrase Goldstone has the bird. However, Goldstone was not in operation at the time of Explorer 1, others claim that the actual phrase was Gold has it. Incorrectly identifying Gold as a tracking station at Earthquake Valley, east of Julian. In fact, Gold Station was located at the Air Force Missile Test Center in Florida, the Goldstone Deep Space Communications Complex conducts tours of its facility and museum to middle and high schools, as well as individuals interested in visiting. The DSS14, Mars telescope is specifically quoted in the webcomic Wondermark, episode 881 In which a Standard is Questioned
6.
Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model
7.
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
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.
Impact event
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An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have found to regularly occur in planetary systems, though the most frequent involve asteroids. Impact craters and structures are dominant landforms on many of the Solar Systems solid objects and present the strongest empirical evidence for their frequency, Impact events appear to have played a significant role in the evolution of the Solar System since its formation. Notable impact events include the Chicxulub impact,66 million years ago, throughout recorded history, hundreds of Earth impacts have been reported, with some occurrences causing deaths, injuries, property damage, or other significant localised consequences. One of the best-known recorded impacts in modern times was the Tunguska event, the Comet Shoemaker–Levy 9 impact provided the first direct observation of an extraterrestrial collision of Solar System objects, when the comet broke apart and collided with Jupiter in July 1994. Impact events have been a plot and background element in science fiction, Impact structures are the result of impact events on solid objects and, as the dominant landforms on many of the Systems solid objects, present the most solid evidence of prehistoric events. Small objects frequently collide with Earth, there is an inverse relationship between the size of the object and the frequency of such events. The lunar cratering record shows that the frequency of impacts decreases as approximately the cube of the craters diameter. Asteroids with a 1 km diameter strike Earth every 500,000 years on average, large collisions – with 5 km objects – happen approximately once every twenty million years. The last known impact of an object of 10 km or more in diameter was at the Cretaceous–Paleogene extinction event 66 million years ago, the energy released by an impactor depends on diameter, density, velocity, and angle. The diameter of most near-Earth asteroids that have not been studied by radar or infrared can generally only be estimated within about a factor of 2 based on the asteroid brightness, the density is generally assumed because the diameter and mass are also generally estimates. The minimum impact velocity on Earth is 11 km/s with asteroid impacts averaging around 17 km/s, the most probable impact angle is 45 degrees. Stony asteroids with a diameter of 4 meters enter Earths atmosphere approximately once per year. Asteroids with a diameter of 7 meters enter the atmosphere about every 5 years with as much energy as the atomic bomb dropped on Hiroshima. These ordinarily explode in the atmosphere and most or all of the solids are vaporized. However, asteroids with a diameter of 20 m, and which strike Earth approximately twice every century, the 2013 Chelyabinsk meteor was estimated to be about 20 m in diameter with an airburst of around 500 kilotons, an explosion 30 times the one over Hiroshima. Much larger objects may impact the solid earth and create a crater, objects with a diameter less than 1 m are called meteoroids and seldom make it to the ground to become meteorites. Although no human is known to have been killed directly by an impact, in 2005 it was estimated that the chance of a single person born today dying due to an impact is around 1 in 200,000
10.
Minimum orbit intersection distance
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Minimum orbit intersection distance is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the orbits of two bodies. Of greatest interest is the risk of a collision with Earth, Earth MOID is often listed on comet and asteroid databases such as the JPL Small-Body Database. MOID values are defined with respect to other bodies as well, Jupiter MOID, Venus MOID. An object is classified as a hazardous object – that is, posing a possible risk to Earth – if, among other conditions. A low MOID does not mean that a collision is inevitable as the planets frequently perturb the orbit of small bodies. It is also necessary that the two bodies reach that point in their orbits at the time before the smaller body is perturbed into a different orbit with a different MOID value. Two Objects gravitationally locked in orbital resonance may never approach one another, numerical integrations become increasingly divergent as trajectories are projected further forward in time, especially beyond times where the smaller body is repeatedly perturbed by other planets. MOID has the convenience that it is obtained directly from the elements of the body. The only object that has ever been rated at 4 on the Torino Scale and this is not the smallest Earth MOID in the catalogues, many bodies with a small Earth MOID are not classed as PHOs because the objects are less than roughly 140 meters in diameter. Earth MOID values are more practical for asteroids less than 140 meters in diameter as those asteroids are very dim. It is even smaller at the more precise JPL Small Body Database
11.
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
12.
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
13.
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
14.
Sentry (monitoring system)
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Whenever a potential impact is detected it will be analyzed and the results immediately published on the Near Earth Object Program. However, several weeks of data are not enough to conclusively identify an impact years in the future. By contrast, eliminating an entry on the page is a negative prediction. Scientists warn against worrying about the possibility of impact with a based on only a few weeks of optical data that show a possible Earth encounter years from now. The Impact Risk page lists a number of lost objects that are, for all purposes, permanent residents of the risk page. 1997 XR2 was serendipitously rediscovered in 2006 after being lost for more than 8 years, some objects on the Sentry Risk Table, such as 2000 SG344, might even be man-made. Notable objects currently on the risk page include,1950 DA,99942 Apophis,101955 Bennu,2009 FD,1994 WR12, and 2010 RF12. Notable asteroids removed from Sentry in the last few years include,2007 VK184,2013 BP73,2008 CK70,2013 TV135,2011 BT15,367943 Duende, and 2011 AG5. The diameter of most near-Earth asteroids that have not been studied by radar or infrared can generally only be estimated within about a factor of 2 based on the absolute magnitude. Their mass, consequently, is uncertain by about a factor of 10, for near-Earth asteroids without a well-determined diameter, Sentry assumes a generic albedo of 0.15. More than two dozen known asteroids have higher than a one in a chance of impacting into Earth within the next 100 years. In August 2013, the Sentry Risk Table started using planetary ephemeris for all NEO orbit determinations, dE431 better models the gravitational perturbations of the planets and includes the 16 most massive main-belt asteroids. JPL launched major changes to the website in February 2017, as of February 2017 there are roughly 680 near-Earth asteroids listed on the risk table and roughly 2000 asteroids have been removed from the risk table since it launched in 2002
15.
Astronomical survey
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An astronomical survey is a general map or image of a region of the sky which lacks a specific observational target. Alternatively, a survey may comprise a set of many images or spectra of objects which share a common type or feature. Surveys have generally performed as part of the production of an astronomical catalog. In some cases, an interested in a particular object will find that survey images are sufficient to make telescope time entirely unnecessary. Surveys also help astronomers obtain observation time on larger, more powerful telescopes, if the astronomer can show a telescope scheduling committee that previous observations support his or her hypothesis, he or she is more likely to be given a chance to make more detailed observations. The wide scope of surveys makes them ideal for astronomers searching for moving objects such as asteroids. An astronomer can compare existing survey images to current observations to locate targets which are in motion, similarly, images of the same object taken by different surveys can be compared to detect transient events such as variable stars. It began in 1977 to 1982 then from 1985 to 1995.3,4.7,12, the telescope is over a thousand times as sensitive as previous infrared surveys. The initial survey, consisting of each sky position imaged at least eight times, was completed by July 2010, 1997–2002 Ohio Sky Survey – Over 19,000 radio sources at 1415 MHz. NVSS – Survey at 1.4 GHz mapping the sky north of −40 deg FIRST – Survey to look for faint radio sources at twenty cms, PALFA Survey – On-going 1.4 GHz survey for radio pulsars using the Arecibo Observatory. 2008–present, the goal for the lifetime is 10 years. The resulting dataset aims to be a resource for studying the physics of the galaxy population. GOODS – The Great Observatories Origins Deep Survey, COSMOS – The Cosmic Evolution Survey. Atlas 3d Survey – sample of 260 galaxies for the Astrophysics project, timeline of astronomical maps, catalogs, and surveys
16.
Kilometre
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The kilometre or kilometer is a unit of length in the metric system, equal to one thousand metres. K is occasionally used in some English-speaking countries as an alternative for the kilometre in colloquial writing. A slang term for the kilometre in the US military is klick, there are two common pronunciations for the word. It is generally preferred by the British Broadcasting Corporation and the Australian Broadcasting Corporation, many scientists and other users, particularly in countries where the metric system is not widely used, use the pronunciation with stress on the second syllable. The latter pronunciation follows the pattern used for the names of measuring instruments. The problem with this reasoning, however, is that the meter in those usages refers to a measuring device. The contrast is more obvious in countries using the British rather than American spelling of the word metre. When Australia introduced the system in 1975, the first pronunciation was declared official by the governments Metric Conversion Board. However, the Australian prime minister at the time, Gough Whitlam, by the 8 May 1790 decree, the Constituent assembly ordered the French Academy of Sciences to develop a new measurement system. In August 1793, the French National Convention decreed the metre as the length measurement system in the French Republic. The first name of the kilometre was Millaire, although the metre was formally defined in 1799, the myriametre was preferred to the kilometre for everyday use. The term myriamètre appeared a number of times in the text of Develeys book Physique dEmile, ou, Principes de la de la nature. French maps published in 1835 had scales showing myriametres and lieues de Poste, the Dutch, on the other hand, adopted the kilometre in 1817 but gave it the local name of the mijl. It was only in 1867 that the term became the only official unit of measure in the Netherlands to represent 1000 metres. In the US, the National Highway System Designation Act of 1995 prohibits the use of highway funds to convert existing signs or purchase new signs with metric units. Although the State DOTs had the option of using metric measurements or dual units, all of them abandoned metric measurements, the Manual on Uniform Traffic Control Devices since 2000 is published in both metric and American Customary Units. Some sporting disciplines feature 1000 m races in major events, but in other disciplines, even though records are catalogued
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Mile
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The mile is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959. The Romans divided their mile into 5,000 feet but the importance of furlongs in pre-modern England meant that the statute mile was made equivalent to 8 furlongs or 5,280 feet in 1593. This form of the mile then spread to the British-colonized nations who continue to employ the mile, the US Geological Survey now employs the metre for official purposes but legacy data from its 1927 geodetic datum has meant that a separate US survey mile continues to see some use. Derived units such as miles per hour and miles per gallon, however, continue to be abbreviated as mph, mpg. The modern English word mile derives from Middle English myl and Old English mīl, the present international mile is usually what is understood by the unqualified term mile. When this distance needs to be distinguished from the nautical mile, in British English, the statute mile may refer to the present international miles or to any other form of English mile since the 1593 Act of Parliament which set it as a distance of 1,760 yards. Under American law, however, the statute mile refers to the US survey mile, the mile has been variously abbreviated—with and without a trailing period—as m, M, ml, and mi. The American National Institute of Standards and Technology now uses and recommends mi in order to avoid confusion with the SI metre and millilitre. Derived units such as miles per hour and miles per gallon, however, continue to be abbreviated in the United States, United Kingdom, the BBC style holds that There is no acceptable abbreviation for ‘miles’ and so it should be spelt out when used in describing areas. The Roman mile consisted of a thousand paces as measured by every other step—as in the distance of the left foot hitting the ground 1,000 times. The ancient Romans, marching their armies through uncharted territory, would push a carved stick in the ground after each 1000 paces. Well-fed and harshly driven Roman legionaries in good weather thus created longer miles, the distance was indirectly standardised by Agrippas establishment of a standard Roman foot in 29 BC, and the definition of a pace as 5 feet. An Imperial Roman mile thus denoted 5,000 Roman feet, surveyors and specialized equipment such as the decempeda and dioptra then spread its use. In modern times, Agrippas Imperial Roman mile was empirically estimated to have been about 1,481 metres in length, in Hellenic areas of the Empire, the Roman mile was used beside the native Greek units as equivalent to 8 stadia of 600 Greek feet. The mílion continued to be used as a Byzantine unit and was used as the name of the zero mile marker for the Byzantine Empire. The Roman mile also spread throughout Europe, with its local variations giving rise to the different units below, also arising from the Roman mile is the milestone. All roads radiated out from the Roman Forum throughout the Empire –50,000 miles of stone-paved roads, at every mile was placed a shaped stone, on which was carved a Roman numeral, indicating the number of miles from the center of Rome – the Forum. Hence, one knew how far one was from Rome
18.
Lunar distance (astronomy)
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Lunar distance is as a unit of measure in astronomy. It is the distance from the center of Earth to the center of the Moon. More technically, it is the mean semi-major axis of the lunar orbit. It may also refer to the distance between the centers of the Earth and the Moon, or less commonly, the instantaneous Earth-Moon distance. The lunar distance is approximately a quarter of a million miles, Lunar distance is also called Earth-Moon distance, Earth–Moon characteristic distance, or distance to the Moon, and commonly indicated with LD or Δ ⊕ L. The mean semi-major axis has a value of 384,402 km, the time-averaged distance between Earth and Moon centers is 385,000.6 km. The actual distance varies over the course of the orbit of the Moon, from 356,500 km at the perigee to 406,700 km at apogee, Lunar distance is commonly used to express the distance to near-Earth object encounters. The measurement is useful in characterizing the lunar radius, the mass of the Sun. Millimeter-precision measurements of the distance are made by measuring the time taken for light to travel between LIDAR stations on the Earth and retroreflectors placed on the Moon. The Moon is spiraling away from the Earth at a rate of 3.8 cm per year. By coincidence, the diameter of corner cubes in retroreflectors on the Moon is also 3.8 cm, the instantaneous lunar distance is constantly changing. In fact the distance between the Moon and Earth can change by as much as 75 m/s, or more than 1,000 kilometers in just 6 hours. There are other effects that influence the lunar distance. Some factors are described in this section, the distance to the Moon can be measured to an accuracy of 2 mm over a 1-hour sampling period, which results in an overall uncertainty of 2–3 cm for the average distance. However, due to its orbit with varying eccentricity, the instantaneous distance varies with monthly periodicity. Furthermore, the distance is perturbed by the effects of various astronomical bodies - most significantly the Sun. Other forces responsible for minuscule perturbations are other planets in the system, asteroids, tidal forces. The effect of pressure from the sun contributes an amount of ±3.6 mm to the lunar distance
19.
Tsunami
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A tsunami or tidal wave, also known as a seismic sea wave, is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Unlike normal ocean waves which are generated by wind, or tides which are generated by the pull of the Moon and Sun. Tsunami waves do not resemble normal undersea currents or sea waves, Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called internal wave train. Wave heights of tens of metres can be generated by large events, numerous terms are used in the English language to describe waves created in a body of water by the displacement of water, however, none of the terms in frequent use are entirely accurate. The term tsunami, meaning harbour wave in literal translation, comes from the Japanese 津波, while not entirely accurate, as tsunami are not restricted to harbours, tsunami is currently the term most widely accepted by geologists and oceanographers. Tsunami are sometimes referred to as tidal waves and this once-popular term derives from the most common appearance of tsunami, which is that of an extraordinarily high tidal bore. Although the meanings of tidal include resembling or having the form or character of the tides, use of the tidal wave is discouraged by geologists. The term seismic sea wave also is used to refer to the phenomenon, prior to the rise of the use of the term tsunami in English-speaking countries, scientists generally encouraged the use of the term seismic sea wave rather than tidal wave. The Sumatran region is not unused to tsunamis either, with earthquakes of varying magnitudes regularly occurring off the coast of the island, Tsunamis are an often underestimated hazard in the Mediterranean Sea and parts of Europe. The tsunami claimed more than 123,000 lives in Sicily, the Storegga Slide in the Norwegian sea and some examples of tsunamis affecting the British Isles refer to landslide and meteotsunamis predominantly and less to earthquake-induced waves. The cause, in my opinion, of this phenomenon must be sought in the earthquake, at the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen, the principal generation mechanism of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is attributed to either earthquakes, landslides, volcanic eruptions, glacier calvings or more rarely by meteorites. The waves formed in this way are then sustained by gravity, tides do not play any part in the generation of tsunamis. Tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water and they grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any state and even at low tide can still inundate coastal areas. On April 1,1946, the 8.6 Mw Aleutian Islands earthquake occurred with a maximum Mercalli intensity of VI and it generated a tsunami which inundated Hilo on the island of Hawaii with a 14-metre high surge. Between 165 and 173 were killed, the area where the earthquake occurred is where the Pacific Ocean floor is subducting under Alaska
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Ocean
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An ocean is a body of saline water that composes much of a planets hydrosphere. On Earth, an ocean is one of the major divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern, the word sea is often used interchangeably with ocean in American English but, strictly speaking, a sea is a body of saline water partly or fully enclosed by land. The ocean contains 97% of Earths water, and oceanographers have stated that less than 5% of the World Ocean has been explored, the total volume is approximately 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the component of Earths hydrosphere, it is integral to all known life, forms part of the carbon cycle. The world ocean is the habitat of 230,000 known species, but because much of it is unexplored, the origin of Earths oceans remains unknown, oceans are thought to have formed in the Hadean period and may have been the impetus for the emergence of life. Extraterrestrial oceans may be composed of water or other elements and compounds, the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many planets and natural satellites, notably. The Solar Systems giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of water within a circumstellar habitable zone. Ocean planets are a type of planet with a surface completely covered with liquid. The concept of Ōkeanós has an Indo-European connection, Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases, though generally described as several separate oceans, these waters comprise one global, interconnected body of salt water sometimes referred to as the World Ocean or global ocean. This concept of a body of water with relatively free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, Oceans are fringed by smaller, adjoining bodies of water such as seas, gulfs, bays, bights, and straits. The Mid-Oceanic Ridge of the World are connected and form the Ocean Ridge, the continuous mountain range is 65,000 km long, and the total length of the oceanic ridge system is 80,000 km long
21.
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
22.
Torino scale
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The Torino Scale is a method for categorizing the impact hazard associated with near-Earth objects such as asteroids and comets. The Palermo Technical Impact Hazard Scale is a similar, but more complex scale, the Torino Scale uses an integer scale from 0 to 10. A0 indicates an object has a small chance of collision with the Earth, compared with the usual background noise of collision events. A10 indicates that a collision is certain, and the object is large enough to precipitate a global disaster. An object is assigned a 0 to 10 value based on its collision probability, the Torino Scale is defined only for potential impacts less than 100 years in the future. For an object with multiple potential collisions on a set of dates and it may be convenient to summarize such an object by the greatest Torino Scale value within the set. The Torino Scale was created by Professor Richard P. Binzel in the Department of Earth, Atmospheric, the Torino Scale has served as the model for the Rio Scale which quantifies the validity and societal impact of SETI data. The Torino Scale also uses a color scale, white, green, yellow, orange. Each color code has a meaning, No object has ever been rated above level 4. The Chicxulub impact, believed by many to be a significant factor in the extinction of the dinosaurs, has estimated at 100 million megatons. The impact which created the Barringer Crater, and the Tunguska event in 1908 are both estimated to be in the 3–10 megaton range, corresponding to Torino Scale 8. The 2013 Chelyabinsk meteor had a kinetic energy prior to impact of about 0.5 megatons. Between 2000 and 2013,26 asteroid impacts with energy of 1-600 kiloton were detected, the biggest hydrogen bomb ever exploded, the Tsar Bomba, was around 50 megatons. The 1883 eruption of Krakatoa was the equivalent of roughly 200 megatons, the impact probability was reduced to ~1,120000 in April 2013, corresponding to Torino Scale 1 or 2. This is a partial list of near-Earth asteroids that have been listed with a Torino Scale rating of 1+ and been lowered to 0 or been removed from the Sentry Risk Table altogether. Most objects that reach a Torino Scale of 1 have an observation arc of less than 2 weeks and are quickly removed as the observation arc gets longer. 20022002 CU11 was rated level 1 on 20 March 2002,20032003 EE16 was rated level 1 on 2 April 2003, and removed from the risk table on 28 May 2003. 2003 MH4 was rated level 1 on 7 July 2003 with an arc of 10 days
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Palermo Technical Impact Hazard Scale
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The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-earth object. It combines two types of data—probability of impact and estimated kinetic yield—into a single hazard value, a rating of 0 means the hazard is equivalent to the background hazard. A rating of +2 would indicate the hazard is 100 times greater than a background event. Scale values less than −2 reflect events for which there are no likely consequences, a similar but less complex scale is the Torino Scale, which is used for simpler descriptions in the non-scientific media. The scale compares the likelihood of the potential impact with the average risk posed by objects of the same size or larger over the years until the date of the potential impact. This average risk from random impacts is known as the background risk, the near-Earth object 2002 NT7 was the first near-Earth object detected by NASAs latest NEO program to be given a positive rating on the scale of 0.06, indicating a higher-than-background threat. The value was lowered after more measurements were taken. So 2002 NT7 is no longer considered to pose any risk and was removed from the Sentry Risk Table on 1 August 2002. In September 2002, the highest Palermo rating was that of asteroid 1950 DA, in August 2014, the rating was reduced to −1.81. For a brief period in late December 2004, asteroid Apophis held the record for Palermo scale values, with a value of 1.10 for a possible collision in the year 2029. The 1.10 value indicated that a collision with this object was considered to be almost 12.6 times more likely than a background event,1 in 37 instead of 1 in 472. With further observation through 2016 there is no significant risk from Apophis at any of the dates in question, the primary reference for the Palermo Technical Scale is Quantifying the risk posed by potential Earth impacts by Chesley et al. Description of the scale NASA list of potential impactors
24.
15P/Finlay
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Comet Finlay is a periodic comet in the solar system discovered by William Henry Finlay on September 26,1886. It came to perihelion on December 27,2014, at apparent magnitude 10. When the first parabolic orbit calculations were made in 1886, there was a similarity between this orbit and that of Francesco de Vicos lost periodic comet of 1844. Lewis Boss noted large discrepancies between the orbits and after further observations concluded that de Vicos comet could not be the same as Finlays, the magnitude of the comet declined after 1926, and it was not until 1953 that it has been observed on every return. During the 2015 perihelion passage the comet outburst on 16 December 2014 from magnitude 11 to magnitude 9 becoming bright enough to be seen in common binoculars with a 50 mm objective lens. On December 23,2014, 15P and Mars were only 1/6 of a degree apart in the sky after sunset, but by December 23,2014, the comet had dimmed considerably since the outburst. On 16 January 2015, the comet outburst to magnitude 8, the comet currently has an Earth-MOID of 0.01 AU. On October 25,2060, the comet will pass roughly 0.04 AU from the Earth
25.
289P/Blanpain
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289P/Blanpain, formerly D/1819 W1 is a short-period comet that was discovered by Jean-Jacques Blanpain on November 28,1819. Blanpain described the comet as having a small and confused nucleus. Another independent discovery was made on December 5 of that year by J. L. Pons, the comet was officially established as periodic comet 289P in July 2013, after being rediscovered by the Pan-STARRS survey during an outburst event. Comet D/1819 W1 has been proposed as the source of the Phoenicid meteor stream. Analysis of the orbits of asteroid 2003 WY25 have supported this conjecture, the comet currently has an Earth-MOID of 0.015 AU. 289P/Blanpain – Seiichi Yoshida @ aerith. net Gary W
26.
255P/Levy
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255P/Levy, formerly P/2006 T1 and P/2011 Y1, is a periodic comet with an orbital period of 5.25 years. It last came to perihelion on 14 January 2012, during the 2006 passage the comet achieved an apparent magnitude of ~9.5. Levy was believed to have recovered on 3 June 2011 at magnitude 19.8. It was most likely a false positive because of large residuals, levy was recovered on 17 December 2011 at magnitude 19.8, and given the second designation 2011 Y1. The last perihelion passage was on 14 January 2012 at a distance of 1.007 AU from the Sun, the comet passed the Earth on 2012-Jan-26 at a distance of 0.2359 AU. MPC estimates after the 2011 recovery estimated that it would reach a magnitude of 17, however, CCD images showed it was diffuse and the comets magnitude was estimated at 14.1 on 30 December 2011. 255P/Levy currently has an Earth-MOID of 0.025 AU
27.
Lincoln Near-Earth Asteroid Research
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LINEAR was responsible for the majority of asteroid discoveries from 1998 until it was overtaken by the Catalina Sky Survey in 2005. As of 15 September 2011, LINEAR had detected 231,082 new small Solar System bodies, the instruments used by the LINEAR program are located at Lincoln Laboratorys Experimental Test Site on the White Sands Missile Range near Socorro, New Mexico. In the late 1970s, the new Lincoln Laboratorys Experimental Test Site facility was built at White Sands Missile Range, the projects prototype used low-light video cameras. In 1994 a new proposal was made for automated detection of asteroids, the wide-field Air Force telescopes were designed for optical observation of Earth-orbiting spacecraft. Initial field tests used a 1024 ×1024 pixel charge-coupled device detector, while this CCD detector filled only about one fifth of the telescopes field of view, four near-earth objects were discovered. A1960 ×2560 pixel CCD which covered the telescopes two-square degree field of view was then installed, the first LINEAR telescope became fully operational in March 1998. Beginning in October 1999, a second 1.0 m telescope was added to the search effort, in 2002, a 0.5 m telescope equipped with the original CCD was brought on-line to provide follow-up observations for the discoveries made by the two search telescopes. This allowed about 20% more of the sky to be searched each night, data recorded by the telescopes is sent to a Lincoln Laboratory facility at Hanscom Air Force Base in Lexington, Massachusetts for processing. Detections are then forwarded to the Minor Planet Center, other objects discovered include 1999 AN10,2002 TD66, and 2004 FH. Stokes, Frank Shelly, Herbert E. M. Viggh, Matthew S. Blythe, and Joseph S. Stuart Near Earth Object program – discovery statistics, Jet Propulsion Laboratory
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Near-Earth Asteroid Tracking
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Near-Earth Asteroid Tracking was a program run by NASA and the Jet Propulsion Laboratory, surveying the sky for near-Earth objects. NEAT was conducted from December 1995 until April 2007, at GEODSS on Hawaii, with the discovery of more than 40 thousand minor planets, NEAT has been one of the most successful programs in this field, comparable to the Catalina Sky Survey, LONEOS and Mount Lemmon Survey. NEAT was the successor of the Palomar Planet-Crossing Asteroid Survey, the original principal investigator was Eleanor F. Helin, with co-investigators Steven H. Pravdo and David L. Rabinowitz. NEAT has an agreement with the U. S. Air Force to use a GEODSS telescope located on Haleakala, Maui. GEODSS stands for Ground-based Electro-Optical Deep Space Surveillance and these wide field Air Force telescopes were designed to optically observe Earth orbital spacecraft, the NEAT team designed a CCD camera and computer system for the GEODSS telescope. The CCD camera format is 4096 ×4096 pixels and the field of view is 1. 2° ×1. 6°, beginning in April 2001, the Samuel Oschin telescope was also put into service to discover and track near-Earth objects. This telescope is equipped with a camera containing 112 CCDs each 2400 ×600 and this is the telescope that produced the images leading to the discovery of 50000 Quaoar in 2002, and 90377 Sedna in 2003 and the dwarf planet Eris. In addition to discovering thousands of asteroids, NEAT is also credited with the co-discovery of periodic comet 54P/de Vico-Swift-NEAT, the C/2001 Q4 comet was discovered on August 24,2001 by NEAT. An asteroid was named in its honour,64070 NEAT, in early 2005,1996 PW was discovered on 1996 August 9 by a NEAT automated search camera on Haleakalā, Hawaii. It was the first object that was not a comet discovered on an orbit typical of a long-period comets. This is raised the possibility it was a comet or a usual asteroid. List of Near-Earth asteroids by distance from Sun Minor Planet Center Planetary Data System Spaceguard Near Earth Asteroid Tracking
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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
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Catalina Sky Survey
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Catalina Sky Survey is a project to discover comets and asteroids, and to search for near-Earth objects. More specifically, CSS is to search for any potentially hazardous asteroids that may pose a threat of impact and its southern hemisphere counterpart, the Siding Spring Survey was closed in 2013 due to loss of funding. CSS supersedes the photographic Bigelow Sky Survey, Catalina Sky Survey utilized two US telescopes, a 1.5 meter f/2 telescope on the peak of Mt. Lemmon, and a 68 cm f/1.7 Schmidt telescope near Mt. Bigelow. The CSS southern hemisphere counterpart, the Siding Spring Survey, used a 0.5 meter f/3 Uppsala Schmidt telescope at Siding Spring Observatory in Australia, all sites use identical, thermo-electrically cooled cameras and common software that was written by the CSS team. The cameras are cooled to approximately −100 °C so their dark current is about 1 electron per hour and these 4096×4096 pixel cameras provide a field of view of 1 degree square on with the 1. 5-m telescope and nearly 9 square degrees with the Catalina Schmidt. Nominal exposures are 30 seconds and the 1. 5-m can reach objects fainter than 21.5 V in that time, CSS typically operates every clear night with the exception of a few nights centered on the full moon. The southern hemispheres SSS in Australia ended in 2013 after funding was discontinued, in 2005, CSS became the most prolific NEO survey surpassing Lincoln Near-Earth Asteroid Research in total number of NEOs and potentially hazardous asteroids discovered each year since. CSS discovered 310 NEOs in 2005,396 in 2006,466 in 2007, for a complete listing of all minor planets discovered by the Catalina Sky Survey, see the index section in list of minor planets. The CSS team is headed by Eric Christensen of the Lunar, the full CSS team is, Robert H. McNaught Gordon J. Garradd The CSS has helped with Astronomy Camp showing campers how they detect NEOs. They even played a role in an exercise with the 2006 Adult Astronomy Camp ending up with a picture that was featured on Astronomy Picture of the Day. Catalina Sky Survey Website Overview and history
31.
Pan-STARRS
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By detecting differences from previous observations of the same areas of the sky, it is expected to discover a very large number of new asteroids, comets, variable stars and other celestial objects. Its primary mission is to detect objects that threaten impact events and is expected to create a database of all objects visible from Hawaii down to apparent magnitude 24. Pan-STARRS is funded in part by the United States Air Force through their Research Labs. Pan-STARRS NEO survey searches all the sky north of declination −47.5, the first Pan-STARRS telescope is located at the summit of Haleakalā on Maui, Hawaii, and went online on December 6,2008, under the administration of the University of Hawaii. Consortium observations for the all sky survey were completed in April 2014, Telescope construction is funded by the U. S. Air Force. Completing the array of four telescopes is estimated at a total cost of US$100 million for the entire array, as of mid-2014, PS2 was in the process of being commissioned. In the wake of substantial funding problems, no clear timeline existed for additional telescopes beyond the second, Pan-STARRS currently consists of two 1.8 m Ritchey–Chrétien telescopes located at Haleakala in Hawaii. The initial telescope, PS1, saw first light using a camera in June 2006. The telescope has a 3° field of view, which is large for telescopes of this size. The focal plane has 60 separately mounted close packed CCDs arranged in an 8 ×8 array, the corner positions are not populated, because the optics do not illuminate the corners. Each CCD device, called an Orthogonal Transfer Array, has 4800 ×4800 pixels, separated into 64 cells and this gigapixel camera or GPC saw first light on August 22,2007, imaging the Andromeda Galaxy. After initial technical difficulties that were mostly solved, PS1 began full operation on May 13,2010. Nick Kaiser, principal investigator of the Pan-STARRS project, summed it up saying “PS1 has been taking science-quality data for six months, the PS1 images however remain slightly less sharp than initially planned, which significantly affects some scientific uses of the data. Each image requires about 2 gigabytes of storage and exposure times will be 30 to 60 seconds, since images will be taken on a continuous basis, it is expected that 10 Terabytes of data will be acquired by PS4 every night. Comparing against a database of known unvarying objects compiled from earlier observations will yield objects of interest, anything that has changed brightness and/or position for any reason. At this time, all funds have been committed The very large field of view of the telescope and the short exposure times enable approximately 6000 square degrees of sky to be imaged every night. Given the need to avoid times when the Moon is bright, this means that an equivalent to the entire sky will be surveyed four times a month. By the end of its initial mission in April 2014
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NASA
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President Dwight D. Eisenhower established NASA in 1958 with a distinctly civilian orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29,1958, disestablishing NASAs predecessor, the new agency became operational on October 1,1958. Since that time, most US space exploration efforts have led by NASA, including the Apollo Moon landing missions, the Skylab space station. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle, the agency is also responsible for the Launch Services Program which provides oversight of launch operations and countdown management for unmanned NASA launches. NASA shares data with various national and international such as from the Greenhouse Gases Observing Satellite. Since 2011, NASA has been criticized for low cost efficiency, from 1946, the National Advisory Committee for Aeronautics had been experimenting with rocket planes such as the supersonic Bell X-1. In the early 1950s, there was challenge to launch a satellite for the International Geophysical Year. An effort for this was the American Project Vanguard, after the Soviet launch of the worlds first artificial satellite on October 4,1957, the attention of the United States turned toward its own fledgling space efforts. This led to an agreement that a new federal agency based on NACA was needed to conduct all non-military activity in space. The Advanced Research Projects Agency was created in February 1958 to develop technology for military application. On July 29,1958, Eisenhower signed the National Aeronautics and Space Act, a NASA seal was approved by President Eisenhower in 1959. Elements of the Army Ballistic Missile Agency and the United States Naval Research Laboratory were incorporated into NASA, earlier research efforts within the US Air Force and many of ARPAs early space programs were also transferred to NASA. In December 1958, NASA gained control of the Jet Propulsion Laboratory, NASA has conducted many manned and unmanned spaceflight programs throughout its history. Some missions include both manned and unmanned aspects, such as the Galileo probe, which was deployed by astronauts in Earth orbit before being sent unmanned to Jupiter, the experimental rocket-powered aircraft programs started by NACA were extended by NASA as support for manned spaceflight. This was followed by a space capsule program, and in turn by a two-man capsule program. This goal was met in 1969 by the Apollo program, however, reduction of the perceived threat and changing political priorities almost immediately caused the termination of most of these plans. NASA turned its attention to an Apollo-derived temporary space laboratory, to date, NASA has launched a total of 166 manned space missions on rockets, and thirteen X-15 rocket flights above the USAF definition of spaceflight altitude,260,000 feet. The X-15 was an NACA experimental rocket-powered hypersonic research aircraft, developed in conjunction with the US Air Force, the design featured a slender fuselage with fairings along the side containing fuel and early computerized control systems
33.
Perturbation (astronomy)
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In astronomy, perturbation is the complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body. The other forces can include a body, resistance, as from an atmosphere. The study of perturbations began with the first attempts to predict planetary motions in the sky, in ancient times the causes were a mystery. Newton, at the time he formulated his laws of motion and of gravitation, applied them to the first analysis of perturbations, the complex motions of gravitational perturbations can be broken down. The hypothetical motion that the body follows under the effect of one other body only is typically a conic section. This is called a problem, or an unperturbed Keplerian orbit. The differences between that and the motion of the body are perturbations due to the additional gravitational effects of the remaining body or bodies. If there is one other significant body then the perturbed motion is a three-body problem. A general analytical solution exists for the problem, when more than two bodies are considered analytic solutions exist only for special cases. Even the two-body problem becomes insoluble if one of the bodies is irregular in shape, most systems that involve multiple gravitational attractions present one primary body which is dominant in its effects. The gravitational effects of the bodies can be treated as perturbations of the hypothetical unperturbed motion of the planet or satellite around its primary body. In methods of general perturbations, general differential equations, either of motion or of change in the elements, are solved analytically, usually by series expansions. The result is expressed in terms of algebraic and trigonometric functions of the orbital elements of the body in question. This can be applied generally to many different sets of conditions, historically, general perturbations were investigated first. The classical methods are known as variation of the elements, variation of parameters or variation of the constants of integration, in these methods, it is considered that the body is always moving in a conic section, however the conic section is constantly changing due to the perturbations. General perturbations is applicable if the perturbing forces are about one order of magnitude smaller, or less. In the Solar System, this is usually the case, Jupiter, general perturbation methods are preferred for some types of problems, as the source of certain observed motions are readily found. In effect, the positions and velocities are perturbed directly, special perturbations can be applied to any problem in celestial mechanics, as it is not limited to cases where the perturbing forces are small
34.
Infrared
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It extends from the nominal red edge of the visible spectrum at 700 nanometers, to 1000000 nm. Most of the radiation emitted by objects near room temperature is infrared. Like all EMR, IR carries radiant energy, and behaves both like a wave and like its quantum particle, the photon, slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has an effect on Earths climate. Infrared radiation is emitted or absorbed by molecules when they change their rotational-vibrational movements and it excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range, Infrared radiation is used in industrial, scientific, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected, Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatuses. Thermal-infrared imaging is used extensively for military and civilian purposes, military applications include target acquisition, surveillance, night vision, homing, and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm, Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers to 1 mm. This range of wavelengths corresponds to a range of approximately 430 THz down to 300 GHz. Below infrared is the portion of the electromagnetic spectrum. Sunlight, at a temperature of 5,780 kelvins, is composed of near thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level, of this energy,527 watts is infrared radiation,445 watts is visible light, and 32 watts is ultraviolet radiation. Nearly all the radiation in sunlight is near infrared, shorter than 4 micrometers. On the surface of Earth, at far lower temperatures than the surface of the Sun, almost all thermal radiation consists of infrared in mid-infrared region, much longer than in sunlight. Of these natural thermal radiation processes only lightning and natural fires are hot enough to produce much visible energy, thermal infrared radiation also has a maximum emission wavelength, which is inversely proportional to the absolute temperature of object, in accordance with Wiens displacement law. Therefore, the band is often subdivided into smaller sections. Due to the nature of the blackbody radiation curves, typical hot objects, such as exhaust pipes, the three regions are used for observation of different temperature ranges, and hence different environments in space
35.
Amateur astronomy
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Amateur astronomy is a hobby whose participants enjoy watching the sky, and the abundance of objects found in it with the unaided eye, binoculars, or telescopes. Many amateurs are beginners or hobbyists, while others have a degree of experience in astronomy and often assist. Amateur astronomers often look at the sky using nothing more than their eyes, people have studied the sky throughout history in an amateur framework, without any formal method of funding. It is only within about the past century, however, that amateur astronomy has become an activity clearly distinguished from professional astronomy, collectively, amateur astronomers observe a variety of celestial objects and phenomena. Common targets of amateur astronomers include the Moon, planets, stars, comets, meteor showers, and a variety of deep sky objects such as clusters, galaxies. Many amateurs like to specialise in observing particular objects, types of objects, one branch of amateur astronomy, amateur astrophotography, involves the taking of photos of the night sky. Most amateur astronomers work at visible wavelengths, but a small minority experiment with wavelengths outside the visible spectrum, non-visual amateur astronomy includes the use of infrared filters on conventional telescopes, and also the use of radio telescopes. Some amateur astronomers use home-made radio telescopes, while others use radio telescopes that were built for astronomy research but have since been made available for use by amateurs. The One-Mile Telescope is one such example, Amateur astronomers use a range of instruments to study the sky, depending on a combination of their interests and resources. Commercial telescopes are available, new and used, but it is common for amateur astronomers to build their own custom telescopes. Some people even focus on amateur telescope making as their primary interest within the hobby of amateur astronomy, although specialized and experienced amateur astronomers tend to acquire more specialized and more powerful equipment over time, relatively simple equipment is often preferred for certain tasks. Amateur astronomers also use star charts that, depending on experience and intentions, Amateur astronomers often like to keep records of their observations, which usually takes the form of an observing log. Observing logs typically record details about which objects were observed and when, sketching is sometimes used within logs, and photographic records of observations have also been used in recent times. The information gathered is used to help studies and interactions between amateur astronomers in yearly gatherings, although not professional information or credible, it is a way for the hobby lovers to share their new sightings and experiences. The Internet is a tool of amateur astronomers. The popularity of CCD imaging among amateurs has led to large numbers of web sites being written by individuals about their images, much of the social interaction of amateur astronomy occurs on mailing lists or discussion groups. Discussion group servers host numerous astronomy lists, a great deal of the commerce of amateur astronomy, the buying and selling of equipment, occurs online. Many amateurs use online tools to plan their observing sessions using tools such as the Clear Sky Chart
36.
Jet Propulsion Laboratory
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The Jet Propulsion Laboratory is a federally funded research and development center and NASA field center in La Cañada Flintridge, California and Pasadena, California, United States. The JPL is managed by the nearby California Institute of Technology for NASA, the laboratorys primary function is the construction and operation of planetary robotic spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASAs Deep Space Network and they are also responsible for managing the JPL Small-Body Database, and provides physical data and lists of publications for all known small Solar System bodies. The JPLs Space Flight Operations Facility and Twenty-Five-Foot Space Simulator are designated National Historic Landmarks, JPL traces its beginnings to 1936 in the Guggenheim Aeronautical Laboratory at the California Institute of Technology when the first set of rocket experiments were carried out in the Arroyo Seco. Malinas thesis advisor was engineer/aerodynamicist Theodore von Kármán, who arranged for U. S. Army financial support for this GALCIT Rocket Project in 1939. In 1941, Malina, Parsons, Forman, Martin Summerfield, in 1943, von Kármán, Malina, Parsons, and Forman established the Aerojet Corporation to manufacture JATO motors. The project took on the name Jet Propulsion Laboratory in November 1943, during JPLs Army years, the laboratory developed two deployed weapon systems, the MGM-5 Corporal and MGM-29 Sergeant intermediate range ballistic missiles. These missiles were the first US ballistic missiles developed at JPL and it also developed a number of other weapons system prototypes, such as the Loki anti-aircraft missile system, and the forerunner of the Aerobee sounding rocket. At various times, it carried out testing at the White Sands Proving Ground, Edwards Air Force Base. A lunar lander was developed in 1938-39 which influenced design of the Apollo Lunar Module in the 1960s. The team lost that proposal to Project Vanguard, and instead embarked on a project to demonstrate ablative re-entry technology using a Jupiter-C rocket. They carried out three successful flights in 1956 and 1957. Using a spare Juno I, the two organizations then launched the United States first satellite, Explorer 1, on February 1,1958, JPL was transferred to NASA in December 1958, becoming the agencys primary planetary spacecraft center. JPL engineers designed and operated Ranger and Surveyor missions to the Moon that prepared the way for Apollo, JPL also led the way in interplanetary exploration with the Mariner missions to Venus, Mars, and Mercury. In 1998, JPL opened the Near-Earth Object Program Office for NASA, as of 2013, it has found 95% of asteroids that are a kilometer or more in diameter that cross Earths orbit. JPL was early to employ women mathematicians, in the 1940s and 1950s, using mechanical calculators, women in an all-female computations group performed trajectory calculations. In 1961, JPL hired Dana Ulery as their first woman engineer to work alongside male engineers as part of the Ranger and Mariner mission tracking teams, when founded, JPLs site was a rocky flood-plain just outside the city limits of Pasadena. Almost all of the 177 acres of the U. S, the city of La Cañada Flintridge, California was incorporated in 1976, well after JPL attained international recognition with a Pasadena address
37.
Albedo
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Albedo is a measure for reflectance or optical brightness. It is dimensionless and measured on a scale from zero to one, surface albedo is defined as the ratio of radiation reflected to the radiation incident on a surface. The proportion reflected is not only determined by properties of the surface itself and these factors vary with atmospheric composition, geographic location and time. While bi-hemispherical reflectance is calculated for an angle of incidence. The temporal resolution may range from seconds to daily, seasonal or annual averages, unless given for a specific wavelength, albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is given for the spectrum in which most solar energy reaches the surface. This spectrum includes visible light, which explains why surfaces with a low albedo appear dark, albedo is an important concept in climatology, astronomy, and environmental management. The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria, any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body, when seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in a range of 0.1 to 0.4. The average albedo of Earth is about 0.3 and this is far higher than for the ocean primarily because of the contribution of clouds. Earths surface albedo is regularly estimated via Earth observation satellite sensors such as NASAs MODIS instruments on board the Terra, thereby, the BRDF allows to translate observations of reflectance into albedo. Earths average surface temperature due to its albedo and the effect is currently about 15 °C. If Earth were frozen entirely, the temperature of the planet would drop below −40 °C. If only the land masses became covered by glaciers, the mean temperature of the planet would drop to about 0 °C. In contrast, if the entire Earth was covered by water — a so-called aquaplanet — the average temperature on the planet would rise to almost 27 °C, hence, the actual albedo α can then be given as, α = α ¯ + D α ¯ ¯. Directional-hemispherical reflectance is sometimes referred to as black-sky albedo and bi-hemispherical reflectance as white-sky albedo and these terms are important because they allow the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface. The albedos of planets, satellites and asteroids can be used to infer much about their properties, the study of albedos, their dependence on wavelength, lighting angle, and variation in time comprises a major part of the astronomical field of photometry
38.
(53319) 1999 JM8
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1999 JM8 is a Potentially hazardous asteroid, near-Earth asteroid and Mars-crosser asteroid discovered by LINEAR. Radar imaging by Goldstone and Arecibo has revealed the asteroid to have a diameter of 6.4 km. Like the asteroid 4179 Toutatis, its speed is unusually slow. It is the largest Potentially hazardous object known and it passed closer than 0.20 AU to the Earth five times in the last century, but its closest approach in the 21st century will be in 2075 at 0.256 AU. Astronomical naming conventions § Minor planets 1999 JM8 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
39.
1566 Icarus
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1566 Icarus is an Apollo asteroid that at perihelion comes closer to the Sun than Mercury, i. e. it is a Mercury-crossing asteroid. It is also a Venus and Mars-crosser and it is named after Icarus of Greek mythology, who flew too close to the Sun. It was discovered on 27 June 1949 by Walter Baade at Palomar Observatory, from 1949 until the discovery of 3200 Phaethon in 1983, it was known as the asteroid that passed closest to the Sun. Icarus is the lowest numbered potentially hazardous asteroid, Icarus makes close approaches to Earth in June at intervals of 9,19, or 28 years. Rarely, it comes as close as 0.042482 AU, during this approach, Icarus became the first minor planet to be observed using radar, with measurements obtained at the Haystack Observatory and the Goldstone Tracking Station. As of 2015, the last close approach was on 16 June 2015, before that, the previous close approach was on 11 June 1996, at 0.10119 AU, almost 40 times as far as the Moon. The next notably close approach will be on 13 June 2043,1566 Icarus is being studied to better understand general relativity, solar oblateness, and Yarkovsky drift. Perihelion precession, caused by general relativity, in the case of Icarus is 10.05 arcseconds per Julian century, Project Icarus was conducted in the spring of 1967. Time magazine ran an article on the endeavor in June 1967, the report later served as the basis and inspiration for the 1979 science fiction film Meteor. com about Project Icarus
40.
Diameter
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In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle, both definitions are also valid for the diameter of a sphere. In more modern usage, the length of a diameter is called the diameter. In this sense one speaks of the rather than a diameter, because all diameters of a circle or sphere have the same length. Both quantities can be calculated efficiently using rotating calipers, for a curve of constant width such as the Reuleaux triangle, the width and diameter are the same because all such pairs of parallel tangent lines have the same distance. For an ellipse, the terminology is different. A diameter of an ellipse is any chord passing through the midpoint of the ellipse, for example, conjugate diameters have the property that a tangent line to the ellipse at the endpoint of one of them is parallel to the other one. The longest diameter is called the major axis, the word diameter is derived from Greek διάμετρος, diameter of a circle, from διά, across, through and μέτρον, measure. It is often abbreviated DIA, dia, d, or ⌀, the definitions given above are only valid for circles, spheres and convex shapes. However, they are cases of a more general definition that is valid for any kind of n-dimensional convex or non-convex object. The diameter of a subset of a space is the least upper bound of the set of all distances between pairs of points in the subset. So, if A is the subset, the diameter is sup, if the distance function d is viewed here as having codomain R, this implies that the diameter of the empty set equals −∞. Some authors prefer to treat the empty set as a case, assigning it a diameter equal to 0. For any solid object or set of scattered points in n-dimensional Euclidean space, in medical parlance concerning a lesion or in geology concerning a rock, the diameter of an object is the supremum of the set of all distances between pairs of points in the object. In differential geometry, the diameter is an important global Riemannian invariant, the symbol or variable for diameter, ⌀, is similar in size and design to ø, the Latin small letter o with stroke. In Unicode it is defined as U+2300 ⌀ Diameter sign, on an Apple Macintosh, the diameter symbol can be entered via the character palette, where it can be found in the Technical Symbols category. The character will not display correctly, however, since many fonts do not include it. In many situations the letter ø is a substitute, which in Unicode is U+00F8 ø
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