1.
Deep Impact (spacecraft)
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Deep Impact was a NASA space probe launched from Cape Canaveral Air Force Station at 18,47 UTC on January 12,2005. It was designed to study the composition of the comet Tempel 1. At 05,52 UTC on July 4,2005, the impactor successfully collided with the comets nucleus, the impact excavated debris from the interior of the nucleus, forming an impact crater. Photographs taken by the spacecraft showed the comet to be more dusty, the impact generated an unexpectedly large and bright dust cloud, obscuring the view of the impact crater. Previous space missions to comets, such as Giotto and Stardust, were fly-by missions and these missions were able to photograph and examine only the surfaces of cometary nuclei, and even then from considerable distances. The Deep Impact mission was the first to eject material from a surface, and the mission garnered large publicity from the media, international scientists. Upon the completion of its mission, proposals were made to further utilize the spacecraft. Consequently, Deep Impact flew by Earth on December 31,2007 on its way to a mission, designated EPOXI, with a dual purpose to study extrasolar planets. By observing the composition of the comet, astronomers hoped to determine how comets form based on the differences between the interior and exterior makeup of the comet, observations of the impact and its aftermath would allow astronomers to attempt to determine the answers to these questions. The missions Principal Investigator was Michael AHearn, an astronomer at the University of Maryland, the Flyby spacecraft is about 3.2 meters long,1.7 meters wide and 2.3 meters high. It includes two panels, a debris shield, and several science instruments for imaging, infrared spectroscopy. The spacecraft also carried two cameras, the High Resolution Imager, and the Medium Resolution Imager.05 to 4.8 micrometres and it has been optimized for observing the comets nucleus. The MRI is the device, and was used primarily for navigation during the final 10-day approach. It also has a wheel, with a slightly different set of filters. The Impactor section of the spacecraft contains an instrument that is identical to the MRI, called the Impactor Targeting Sensor. Its dual purpose was to sense the Impactors trajectory, which could then be adjusted up to four times between release and impact, and to image the comet from close range, the final image taken by the impactor was snapped only 3.7 seconds before impact. The impactors payload, dubbed the Cratering Mass, was 100% copper, including this cratering mass, copper formed 49% of total mass of the impactor, this was to minimize interference with scientific measurements. Since copper was not expected to be found on a comet, instead of using explosives, it was also cheaper to use copper as the payload
2.
Wilhelm Tempel
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Ernst Wilhelm Leberecht Tempel, normally known as Wilhelm Tempel, was a German astronomer who worked in Marseille until the outbreak of the Franco-Prussian War in 1870, then later moved to Italy. Tempel was born at Niedercunnersdorf, Saxony, other periodic comets that bear his name include 10P/Tempel and 11P/Tempel-Swift-LINEAR. He won the Prix Valz for the year 1880, the main-belt asteroid 3808 Tempel and the lunar crater Tempel are named after him. Bianchi, S. Gasperini, A. Galli, D. Palla, F. Brenni, P. Giatti, A. Wilhelm Tempel, journal of Astronomical History and Heritage. Monthly Notices of the Royal Astronomical Society, W. Tempel @ Astrophysics Data System
3.
Apsis
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An apsis is an extreme point in an objects orbit. The word comes via Latin from Greek and is cognate with apse, for elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- and ap-, or apo- added to a reference to the thing being orbited. For a body orbiting the Sun, the point of least distance is the perihelion, the terms become periastron and apastron when discussing orbits around other stars. For any satellite of Earth including the Moon the point of least distance is the perigee, for objects in Lunar orbit, the point of least distance is the pericynthion and the greatest distance the apocynthion. For any orbits around a center of mass, there are the terms pericenter and apocenter, periapsis and apoapsis are equivalent alternatives. A straight line connecting the pericenter and apocenter is the line of apsides and this is the major axis of the ellipse, its greatest diameter. For a two-body system the center of mass of the lies on this line at one of the two foci of the ellipse. When one body is larger than the other it may be taken to be at this focus. Historically, in systems, apsides were measured from the center of the Earth. In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body. However, in the case of spacecraft, the family of terms are used to refer to the orbital altitude of the spacecraft from the surface of the central body. The arithmetic mean of the two limiting distances is the length of the axis a. The geometric mean of the two distances is the length of the semi-minor axis b, the geometric mean of the two limiting speeds is −2 ε = μ a which is the speed of a body in a circular orbit whose radius is a. The words pericenter and apocenter are often seen, although periapsis/apoapsis are preferred in technical usage, various related terms are used for other celestial objects. The -gee, -helion and -astron and -galacticon forms are used in the astronomical literature when referring to the Earth, Sun, stars. The suffix -jove is occasionally used for Jupiter, while -saturnium has very rarely used in the last 50 years for Saturn. The -gee form is used as a generic closest approach to planet term instead of specifically applying to the Earth. During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon, regarding black holes, the term peri/apomelasma was used by physicist Geoffrey A. Landis in 1998 before peri/aponigricon appeared in the scientific literature in 2002
4.
Semi-major and semi-minor axes
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In geometry, the major axis of an ellipse is its longest diameter, a line segment that runs through the center and both foci, with ends at the widest points of the perimeter. The semi-major axis is one half of the axis, and thus runs from the centre, through a focus. Essentially, it is the radius of an orbit at the two most distant points. For the special case of a circle, the axis is the radius. One can think of the axis as an ellipses long radius. The semi-major axis of a hyperbola is, depending on the convention, thus it is the distance from the center to either vertex of the hyperbola. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction. Thus a and b tend to infinity, a faster than b, the semi-minor axis is a line segment associated with most conic sections that is at right angles with the semi-major axis and has one end at the center of the conic section. It is one of the axes of symmetry for the curve, in an ellipse, the one, in a hyperbola. The semi-major axis is the value of the maximum and minimum distances r max and r min of the ellipse from a focus — that is. In astronomy these extreme points are called apsis, the semi-minor axis of an ellipse is the geometric mean of these distances, b = r max r min. The eccentricity of an ellipse is defined as e =1 − b 2 a 2 so r min = a, r max = a. Now consider the equation in polar coordinates, with one focus at the origin, the mean value of r = ℓ / and r = ℓ /, for θ = π and θ =0 is a = ℓ1 − e 2. In an ellipse, the axis is the geometric mean of the distance from the center to either focus. The semi-minor axis of an ellipse runs from the center of the ellipse to the edge of the ellipse, the semi-minor axis is half of the minor axis. The minor axis is the longest line segment perpendicular to the axis that connects two points on the ellipses edge. The semi-minor axis b is related to the axis a through the eccentricity e. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction
5.
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
6.
Orbital eccentricity
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The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is an orbit, values between 0 and 1 form an elliptical orbit,1 is a parabolic escape orbit. The term derives its name from the parameters of conic sections and it is normally used for the isolated two-body problem, but extensions exist for objects following a rosette orbit through the galaxy. In a two-body problem with inverse-square-law force, every orbit is a Kepler orbit, the eccentricity of this Kepler orbit is a non-negative number that defines its shape. The limit case between an ellipse and a hyperbola, when e equals 1, is parabola, radial trajectories are classified as elliptic, parabolic, or hyperbolic based on the energy of the orbit, not the eccentricity. Radial orbits have zero angular momentum and hence eccentricity equal to one, keeping the energy constant and reducing the angular momentum, elliptic, parabolic, and hyperbolic orbits each tend to the corresponding type of radial trajectory while e tends to 1. For a repulsive force only the trajectory, including the radial version, is applicable. For elliptical orbits, a simple proof shows that arcsin yields the projection angle of a circle to an ellipse of eccentricity e. For example, to view the eccentricity of the planet Mercury, next, tilt any circular object by that angle and the apparent ellipse projected to your eye will be of that same eccentricity. From Medieval Latin eccentricus, derived from Greek ἔκκεντρος ekkentros out of the center, from ἐκ- ek-, eccentric first appeared in English in 1551, with the definition a circle in which the earth, sun. Five years later, in 1556, a form of the word was added. The eccentricity of an orbit can be calculated from the state vectors as the magnitude of the eccentricity vector, e = | e | where. For elliptical orbits it can also be calculated from the periapsis and apoapsis since rp = a and ra = a, where a is the semimajor axis. E = r a − r p r a + r p =1 −2 r a r p +1 where, rp is the radius at periapsis. For Earths annual orbit path, ra/rp ratio = longest_radius / shortest_radius ≈1.034 relative to center point of path, the eccentricity of the Earths orbit is currently about 0.0167, the Earths orbit is nearly circular. Venus and Neptune have even lower eccentricity, over hundreds of thousands of years, the eccentricity of the Earths orbit varies from nearly 0.0034 to almost 0.058 as a result of gravitational attractions among the planets. The table lists the values for all planets and dwarf planets, Mercury has the greatest orbital eccentricity of any planet in the Solar System. Such eccentricity is sufficient for Mercury to receive twice as much solar irradiation at perihelion compared to aphelion, before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit
7.
Orbital inclination
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Orbital inclination measures the tilt of an objects orbit around a celestial body. It is expressed as the angle between a plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the equator, the plane of the orbit is the same as the Earths equatorial plane. The general case is that the orbit is tilted, it spends half an orbit over the northern hemisphere. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°, the inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit. It is the angle between the plane and the plane of reference, normally stated in degrees. For a satellite orbiting a planet, the plane of reference is usually the plane containing the planets equator, for planets in the Solar System, the plane of reference is usually the ecliptic, the plane in which the Earth orbits the Sun. This reference plane is most practical for Earth-based observers, therefore, Earths inclination is, by definition, zero. Inclination could instead be measured with respect to another plane, such as the Suns equator or the invariable plane, the inclination of orbits of natural or artificial satellites is measured relative to the equatorial plane of the body they orbit, if they orbit sufficiently closely. The equatorial plane is the perpendicular to the axis of rotation of the central body. An inclination of 30° could also be described using an angle of 150°, the convention is that the normal orbit is prograde, an orbit in the same direction as the planet rotates. Inclinations greater than 90° describe retrograde orbits, thus, An inclination of 0° means the orbiting body has a prograde orbit in the planets equatorial plane. An inclination greater than 0° and less than 90° also describe prograde orbits, an inclination of 63. 4° is often called a critical inclination, when describing artificial satellites orbiting the Earth, because they have zero apogee drift. An inclination of exactly 90° is an orbit, in which the spacecraft passes over the north and south poles of the planet. An inclination greater than 90° and less than 180° is a retrograde orbit, an inclination of exactly 180° is a retrograde equatorial orbit. For gas giants, the orbits of moons tend to be aligned with the giant planets equator, the inclination of exoplanets or members of multiple stars is the angle of the plane of the orbit relative to the plane perpendicular to the line-of-sight from Earth to the object. An inclination of 0° is an orbit, meaning the plane of its orbit is parallel to the sky. An inclination of 90° is an orbit, meaning the plane of its orbit is perpendicular to the sky
8.
Comet nucleus
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The nucleus is the solid, central part of a comet, popularly termed a dirty snowball or an icy dirtball. A cometary nucleus is composed of rock, dust, and frozen gases, when heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Suns radiation pressure and solar wind cause an enormous tail to form, a typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust, comets, or their precursors, formed in the outer Solar System, possibly millions of years before planet formation. How and when formed is debated, with distinct implications for Solar System formation, dynamics. Three-dimensional computer simulations indicate the structural features observed on cometary nuclei can be explained by pairwise low velocity accretion of weak cometesimals. The currently favored creation mechanism is that of the nebular hypothesis, astronomers think that comets originate in both the Oort cloud and the scattered disk. Most cometary nuclei are thought to be no more than about 10 miles across, the largest comets that have come inside the orbit of Saturn are C/2002 VQ94, Hale–Bopp, 29P, 109P/Swift–Tuttle, and 28P/Neujmin. The potato-shaped nucleus of Halleys comet contains equal amounts of ice, during a flyby in September 2001, the Deep Space 1 spacecraft observed the nucleus of Comet Borrelly and found it to be about half the size of the nucleus of Halleys Comet. Borrellys nucleus was also potato-shaped and had a black surface. Like Halleys Comet, Comet Borrelly only released gas from small areas where holes in the crust exposed the ice to sunlight, the nucleus of comet Hale–Bopp was estimated to be 60 ±20 km in diameter. Hale-Bopp appeared bright to the eye because its unusually large nucleus gave off a great deal of dust. The nucleus of P/2007 R5 is probably only 100–200 meters in diameter, the largest centaurs are estimated to be 250 km to 300 km in diameter. Three of the largest would include 10199 Chariklo,2060 Chiron, known comets have been estimated to have an average density of 0.6 g/cm3. Below is a list of comets that have had estimated sizes, densities, about 80% of the Halleys Comet nucleus is water ice, and frozen carbon monoxide makes up another 15%. Much of the remainder is carbon dioxide, methane. Scientists think that comets are chemically similar to Halleys Comet. The nucleus of Halleys Comet is also a dark black
9.
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
10.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
11.
Stardust (spacecraft)
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Stardust was a 300-kilogram robotic space probe launched by NASA on February 7,1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust and it was the first sample return mission of its kind. En route to comet Wild 2, the craft also flew by, the primary mission was successfully completed on January 15,2006, when the sample return capsule returned to Earth. A mission extension codenamed NExT culminated in February 2011 with Stardust intercepting comet Tempel 1, Stardust ceased operations in March 2011. On August 14,2014, scientists announced the identification of possible interstellar dust particles from the Stardust capsule returned to Earth in 2006, beginning in the 1980s, scientists began seeking a dedicated mission to study a comet. During the early 1990s, several missions to study comet Halley became the first successful missions to return close-up data, however, the US cometary mission, Comet Rendezvous Asteroid Flyby, was canceled for budgetary reasons. In the mid-1990s, further support was given to a cheaper, Stardust was competitively selected in the fall of 1995 as a NASA Discovery Program mission of low-cost with highly focused science goals. Construction of Stardust began in 1996, and was subject to the maximum contamination restriction, Comet Wild 2 was selected as the primary target of the mission for the rare chance to observe a long-period comet that has ventured close to the Sun. The comet has since become a short period comet after an event in 1974, in planning the mission, it was expected that most of the original material from which the comet formed would still be preserved. Facilitating the intercept of significant numbers of interstellar dust particles using the collection medium. Returning as many high resolution images of the coma and nucleus as possible. The spacecraft was designed, built and operated by Lockheed Martin Astronautics as a Discovery-class mission in Denver, JPL provided mission management for the NASA division for mission operations. The principal investigator of the mission was Dr. Donald Brownlee from the University of Washington, the spacecraft bus measured 1.7 meters in length, and 0.66 meters in width, a design adapted from the SpaceProbe deep space bus developed by Lockheed Martin Astronautics. To maintain low costs, the spacecraft incorporated many designs and technologies used in past missions or previously developed for missions by the Small Spacecraft Technologies Initiative. The spacecraft featured five scientific instruments to collect data, including the Stardust Sample Collection tray, the spacecraft was launched with 80-kilograms of propellant. Information for spacecraft positioning was provided by a camera using FSW to determine attitude, an inertial measurement unit. The probe was powered by two arrays, providing an average of 330 watts of power. The arrays also included Whipple shields to protect the surfaces from the potentially damaging cometary dust while the spacecraft was in the coma of Wild 2
12.
Marseille
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Marseille, also known as Marseilles in English, is a city in France. Known to the ancient Greeks and Romans as Massalia, Marseille was the most important trading centre in the region, Marseille is now Frances largest city on the Mediterranean coast and the largest port for commerce, freight and cruise ships. The city was European Capital of Culture, together with Košice, Slovakia and it hosted the European Football Championship in 2016, and will be the European Capital of Sport in 2017. The city is home to campuses of Aix-Marseille University and part of one of the largest metropolitan conurbations in France. Marseille is the second largest city in France after Paris and the centre of the third largest metropolitan area in France after Paris, further east still are the Sainte-Baume, the city of Toulon and the French Riviera. To the north of Marseille, beyond the low Garlaban and Etoile mountain ranges, is the 1,011 m Mont Sainte Victoire. To the west of Marseille is the artists colony of lEstaque, further west are the Côte Bleue, the Gulf of Lion. The airport lies to the north west of the city at Marignane on the Étang de Berre, the citys main thoroughfare stretches eastward from the Old Port to the Réformés quarter. Two large forts flank the entrance to the Old Port—Fort Saint-Nicolas on the south side and Fort Saint-Jean on the north. Further out in the Bay of Marseille is the Frioul archipelago which comprises four islands, one of which, If, is the location of Château dIf, the main commercial centre of the city intersects with the Canebière at rue St Ferréol and the Centre Bourse. To the south east of central Marseille in the 6th arrondissement are the Prefecture and the fountain of Place Castellane. To the south west are the hills of the 7th arrondissement, the railway station—Gare de Marseille Saint-Charles—is north of the Centre Bourse in the 1st arrondissement, it is linked by the Boulevard dAthènes to the Canebière. Marseille has a Mediterranean climate with mild, humid winters and warm to hot, december, January, and February are the coldest months, averaging temperatures of around 12 °C during the day and 4 °C at night. Marseille is officially the sunniest major city in France with over 2,900 hours of sunshine while the average sunshine in France is around 1,950 hours, less frequent is the Sirocco, a hot, sand-bearing wind, coming from the Sahara Desert. Snowfalls are infrequent, over 50% of years do not experience a single snowfall, Massalia, whose name was probably adapted from an existing language related to Ligurian, was the first Greek settlement in France. It was established within modern Marseille around 600 BC by colonists coming from Phocaea on the Aegean coast of Asia Minor. The connection between Massalia and the Phoceans is mentioned in Thucydidess Peloponnesian War, he notes that the Phocaean project was opposed by the Carthaginians, the founding of Massalia has also been recorded as a legend. Protis was invited inland to a banquet held by the chief of the local Ligurian tribe for suitors seeking the hand of his daughter Gyptis in marriage, at the end of the banquet, Gyptis presented the ceremonial cup of wine to Protis, indicating her unequivocal choice
13.
Perihelion and aphelion
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The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory
14.
Lost comet
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The D/ designation is for a periodic comet that no longer exists or is deemed to have disappeared. Some astronomers have specialized in this area, such as Brian G. Marsden, there are a number of reasons why a comet might be missed by astronomers during subsequent apparitions. Firstly, cometary orbits may be perturbed by interaction with the giant planets and this, along with nongravitational forces, can result in changes to the date of perihelion. As some comets periodically undergo outbursts or flares in brightness, it may be possible for a faint comet to be discovered during an outburst. Comets can also run out of volatiles and this may have occurred in the case of 5D/Brorsen, which was considered by Marsden to have probably faded out of existence in the late 19th century. Comets are in some known to have disintegrated during their perihelion passage. The best-known example is Bielas Comet, which was observed to split into two components before disappearing after its 1852 apparition, in modern times 73P/Schwassmann–Wachmann has been observed in the process of breaking up. In the case of lost comets this is especially tricky, for example, the comet 177P/Barnard, discovered by Edward Emerson Barnard on June 24,1889, was rediscovered after 116 years in 2006. On July 19,2006, 177P came within 0.36 AU of the Earth, comets can be gone but not considered lost, even though they may not be expected back for hundreds or even thousands of years. With more powerful telescopes it has become possible to observe comets for longer periods of time after perihelion, for example, Comet Hale–Bopp was observable with the naked eye about 18 months after its approach in 1997. It is expected to remain observable with large telescopes until perhaps 2020, comets that have been lost or which have disappeared have names beginning with a D according to current IAU conventions. Comets are typically observed on a periodic return, when they do not they are sometimes found again, while other times they may break up into fragments. These fragments can sometimes be observed, but the comet is no longer expected to return. Other times a comet will not be considered lost until it does not appear at a predicted time, comets may also collide with another object, such as Comet Shoemaker–Levy 9, which collided with Jupiter in 1994
15.
Jupiter
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Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, Jupiter and Saturn are gas giants, the other two giant planets, Uranus and Neptune are ice giants. Jupiter has been known to astronomers since antiquity, the Romans named it after their god Jupiter. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium and it may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rotation, the planets shape is that of an oblate spheroid. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence, a prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere, Jupiter has at least 67 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. In late February 2007, Jupiter was visited by the New Horizons probe, the latest probe to visit the planet is Juno, which entered into orbit around Jupiter on July 4,2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon Europa, Earth and its neighbor planets may have formed from fragments of planets after collisions with Jupiter destroyed those super-Earths near the Sun. Astronomers have discovered nearly 500 planetary systems with multiple planets, Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth. Jupiter is composed primarily of gaseous and liquid matter and it is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of 142,984 km at its equator, the average density of Jupiter,1.326 g/cm3, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiters upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, a helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiters atmosphere is approximately 75% hydrogen and 24% helium by mass, the atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, the outermost layer of the atmosphere contains crystals of frozen ammonia. The interior contains denser materials - by mass it is roughly 71% hydrogen, 24% helium, through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found
16.
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
17.
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
18.
Libration
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Lunar libration is distinct from the slight changes in the Moons visual size as seen from Earth. Although this appearance can also be described as a motion, libration is caused by actual changes in the physical distance of the Moon. The Moon generally has one hemisphere facing the Earth, due to tidal locking, therefore, humans first view of the far side of the Moon resulted from lunar exploration on October 7,1959. However, this picture is only approximately true, over time. Libration is manifested as a slow rocking back and forth of the Moon as viewed from Earth, libration in latitude results from a slight inclination between the Moons axis of rotation and the normal to the plane of its orbit around Earth. Its origin is analogous to how the seasons arise from Earths revolution about the Sun. In 1772 Lagranges analyses determined that small bodies can stably share the orbit as a planet if they remain near Lagrange points. Such ‘trojan asteroids’ have been found co-orbiting with Earth, Jupiter, Mars, trojan asteroids associated with Earth are difficult to observe in the visible spectrum, as their libration paths are such that they would be visible primarily in the daylight sky. In 2010, however, using infrared observation techniques, the asteroid 2010 TK7 was found to be a companion of the Earth, it librates around the leading Lagrange point, L4
19.
Elizabeth Roemer
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Elizabeth Roemer was an American astronomer whose research interests centered on comets and asteroids. Roemer was a professor at the University of Arizona and she discovered the two main-belt asteroids 1930 Lucifer and 1983 Bok. In addition, she took a set of photographic plates of comets over 25 years. She recovered 79 returning short period comets during her career, in 1975, she also co-discovered Themisto, one of the 67 moons of Jupiter. The inner main-belt asteroid 1657 Roemera, discovered by Swiss astronomer Paul Wild in 1961, was named in her honor, lunar and Planetary Laboratory, Elizabeth Roemer
20.
Steward Observatory
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Steward Observatory is the research arm of the Department of Astronomy at the University of Arizona. Its offices are located on the UA campus in Tucson, Arizona, established in 1916, the first telescope and building were formally dedicated on April 23,1923. It now operates, or is a partner in telescopes at five locations in Arizona, one in New Mexico, one in Hawaii. It has provided instruments for three different space telescopes and numerous terrestrial ones, Steward also has one of the few facilities in the world that can cast and figure the very large primary mirrors used in telescopes built in the past decade. Steward Observatory owes its existence to the efforts of American astronomer, in 1906, Douglass accepted a position as Assistant Professor of Physics and Geography at the University of Arizona in Tucson, Arizona. Over the next 10 years, all of Douglass’ efforts to secure funding from the University and the Arizona Territorial Legislatures ended in failure. During this time period, Douglass served the University of Arizona as Head of the Dept. of Physics and Astronomy, Interim President, and finally Dean of the College of Letters, Arts, & Sciences. Then on October 18,1916, University President Rufus von KleinSmid announced that a donor had given the University $60,000 “…to be used to buy a telescope of huge size. ”That donor was later revealed to be Mrs. Lavinia Steward of Oracle. Mrs. Steward was a widow who had an interest in astronomy. Douglass made plans to use the Steward gift to construct a 36-inch diameter Newtonian reflecting telescope, the situation was further delayed by the fact that up until this time, the expertise in large telescope mirror making was in Europe. The war made it impossible to contract with a European company, so Douglass had to find an American glass company that was willing to develop this expertise. After a couple of failed castings, the Spencer Lens Co. of Buffalo, the telescope was finally installed in the observatory building in July 1922, and the Steward Observatory was officially dedicated on April 23,1923. This installation is to be devoted to scientific research, scientific research is business foresight on a large scale. It is knowledge obtained before it is needed and this I believe is the essence of education wherever such education is not strictly vocational. The student learns many facts and has much training, so it is with the research institutions. In this Observatory I sincerely hope and expect that the boundaries of knowledge will be advanced along astronomical lines. Astronomy was the first science developed by our primitive ancestors thousands of years ago because it measured time, Steward Observatory manages three different observing locations in southern Arizona, Mount Graham International Observatory, Mount Lemmon Observatory, and Catalina Station on Mount Bigelow. It also operates telescopes at two additional important observatories, Kitt Peak National Observatory and Fred Lawrence Whipple Observatory on Mount Hopkins, Steward is a partner in the Sloan Digital Sky Survey-III, which is located in New Mexico at Apache Point Observatory
21.
Chandra X-ray Observatory
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The Chandra X-ray Observatory, previously known as the Advanced X-ray Astrophysics Facility, is a Flagship-class space observatory launched on STS-93 by NASA on July 23,1999. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, since the Earths atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes, therefore space-based telescopes are required to make these observations. Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2017, Chandra is one of the Great Observatories, along with the Hubble Space Telescope, Compton Gamma Ray Observatory, and the Spitzer Space Telescope. The telescope is named after astrophysicist Subrahmanyan Chandrasekhar, in 1976 the Chandra X-ray Observatory was proposed to NASA by Riccardo Giacconi and Harvey Tananbaum. Preliminary work began the year at Marshall Space Flight Center. In the meantime, in 1978, NASA launched the first imaging X-ray telescope, Einstein, work continued on the AXAF project throughout the 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned, four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. AXAFs planned orbit was changed to a one, reaching one third of the way to the Moons at its farthest point. This eliminated the possibility of improvement or repair by the space shuttle, AXAF was assembled and tested by TRW in Redondo Beach, California. AXAF was renamed Chandra as part of a contest held by NASA in 1998, the contest winners, Jatila van der Veen and Tyrel Johnson, suggested the name in honor of Nobel Prize–winning Indian-American astrophysicist Subrahmanyan Chandrasekhar. He is known for his work in determining the mass of white dwarf stars, leading to greater understanding of high energy astronomical phenomena such as neutron stars. Originally scheduled to be launched in December 1998, the spacecraft was delayed several months, Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in Cambridge, Massachusetts, with assistance from MIT, the ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the focal plane during passages. Although Chandra was initially given a lifetime of 5 years. Physically Chandra could last much longer, a study performed at the Chandra X-ray Center indicated that the observatory could last at least 15 years. In July 2008, the International X-ray Observatory, a joint project between ESA, NASA and JAXA, was proposed as the next major X-ray observatory but was later cancelled, ESA later resurrected the project as the Advanced Telescope for High Energy Astrophysics with a proposed launch in 2028. The data gathered by Chandra has greatly advanced the field of X-ray astronomy, in the Crab Nebula, another supernova remnant, Chandra showed a never-before-seen ring around the central pulsar and jets that had only been partially seen by earlier telescopes
22.
Apparent magnitude
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The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value, the Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere, furthermore, the magnitude scale is logarithmic, a difference of one in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry, apparent magnitudes are used to quantify the brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or often simply as V, the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the sky were said to be of first magnitude, whereas the faintest were of sixth magnitude. Each grade of magnitude was considered twice the brightness of the following grade and this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to have originated with Hipparchus. This implies that a star of magnitude m is 2.512 times as bright as a star of magnitude m +1 and this figure, the fifth root of 100, became known as Pogsons Ratio. The zero point of Pogsons scale was defined by assigning Polaris a magnitude of exactly 2. However, with the advent of infrared astronomy it was revealed that Vegas radiation includes an Infrared excess presumably due to a disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures, however, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the scale was extrapolated to all wavelengths on the basis of the black body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, with the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30, astronomers have developed other photometric zeropoint systems as alternatives to the Vega system. The AB magnitude zeropoint is defined such that an objects AB, the dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor 5√100 ≈2.512. Inverting the above formula, a magnitude difference m1 − m2 = Δm implies a brightness factor of F2 F1 =100 Δ m 5 =100.4 Δ m ≈2.512 Δ m
23.
Hubble Space Telescope
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The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Although not the first space telescope, Hubble is one of the largest and most versatile, with a 2. 4-meter mirror, Hubbles four main instruments observe in the near ultraviolet, visible, and near infrared spectra. Hubbles orbit outside the distortion of Earths atmosphere allows it to take extremely high-resolution images, Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as determining the rate of expansion of the universe. The HST was built by the United States space agency NASA, the Space Telescope Science Institute selects Hubbles targets and processes the resulting data, while the Goddard Space Flight Center controls the spacecraft. Space telescopes were proposed as early as 1923, Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster. When finally launched in 1990, Hubbles main mirror was found to have been ground incorrectly, the optics were corrected to their intended quality by a servicing mission in 1993. Hubble is the telescope designed to be serviced in space by astronauts. After launch by Space Shuttle Discovery in 1990, five subsequent Space Shuttle missions repaired, upgraded, the fifth mission was canceled on safety grounds following the Columbia disaster. However, after spirited public discussion, NASA administrator Mike Griffin approved the fifth servicing mission, the telescope is operating as of 2017, and could last until 2030–2040. Its scientific successor, the James Webb Space Telescope, is scheduled for launch in 2018, the history of the Hubble Space Telescope can be traced back as far as 1946, to the astronomer Lyman Spitzers paper Astronomical advantages of an extraterrestrial observatory. In it, he discussed the two advantages that a space-based observatory would have over ground-based telescopes. First, the resolution would be limited only by diffraction, rather than by the turbulence in the atmosphere. Second, a telescope could observe infrared and ultraviolet light. Spitzer devoted much of his career to pushing for the development of a space telescope, space-based astronomy had begun on a very small scale following World War II, as scientists made use of developments that had taken place in rocket technology. An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel space program, oAO-1s battery failed after three days, terminating the mission. It was followed by OAO-2, which carried out observations of stars and galaxies from its launch in 1968 until 1972. The continuing success of the OAO program encouraged increasingly strong consensus within the community that the LST should be a major goal
24.
Spitzer Space Telescope
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The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility, is an infrared space telescope launched in 2003. It is the fourth and final of the NASA Great Observatories program, the planned mission period was to be 2.5 years with a pre-launch expectation that the mission could extend to five or slightly more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009, without liquid helium to cool the telescope to the very low temperatures needed to operate, most of the instruments are no longer usable. All Spitzer data, from both the primary and warm phases, are archived at the Infrared Science Archive, in keeping with NASA tradition, the telescope was renamed after its successful demonstration of operation, on 18 December 2003. Unlike most telescopes that are named after famous deceased astronomers by a board of scientists, the contest led to the telescope being named in honor of astronomer Lyman Spitzer, who had promoted the concept of space telescopes in the 1940s. Spitzer wrote a 1946 report for RAND Corporation describing the advantages of an extraterrestrial observatory, the US$720 million Spitzer was launched on 25 August 2003 at 05,35,39 UTC from Cape Canaveral SLC-17B aboard a Delta II 7920H rocket. It follows a heliocentric instead of orbit, trailing and drifting away from Earths orbit at approximately 0.1 astronomical unit per year. The primary mirror is 85 centimeters in diameter, f/12, made of beryllium and was cooled to 5.5 K, by the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of Earths atmosphere. Anticipating the major results from an upcoming Explorer satellite and from the Shuttle mission, long-duration spaceflights of infrared telescopes cooled to cryogenic temperatures. Earlier infrared observations had been made by both space-based and ground-based observatories, ground-based observatories have the drawback that at infrared wavelengths or frequencies, both the Earths atmosphere and the telescope itself will radiate strongly. Additionally, the atmosphere is opaque at most infrared wavelengths and this necessitates lengthy exposure times and greatly decreases the ability to detect faint objects. It could be compared to trying to observe the stars at noon, previous space observatories were launched during the 1980s and 1990s and great advances in astronomical technology have been made since then. Most of the early concepts envisioned repeated flights aboard the NASA Space Shuttle and this approach was developed in an era when the Shuttle program was expected to support weekly flights of up to 30 days duration. A May 1983 NASA proposal described SIRTF as a Shuttle-attached mission, several flights were anticipated with a probable transition into a more extended mode of operation, possibly in association with a future space platform or space station. SIRTF would be a 1-meter class, cryogenically cooled, multi-user facility consisting of a telescope, the first flight was expected to occur about 1990, with the succeeding flights anticipated beginning approximately one year later. By September 1983 NASA was considering the possibility of a long duration SIRTF mission, Spitzer is the only one of the Great Observatories not launched by the Space Shuttle, as was originally intended. However, after the 1986 Challenger disaster, the Centaur LH2–LOX upper stage, the mission underwent a series of redesigns during the 1990s, primarily due to budget considerations. This resulted in a smaller but still fully capable mission that could use the smaller Delta II expendable launch vehicle
25.
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
26.
Coordinated Universal Time
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Coordinated Universal Time, abbreviated to UTC, is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean time at 0° longitude. It is one of closely related successors to Greenwich Mean Time. For most purposes, UTC is considered interchangeable with GMT, the first Coordinated Universal Time was informally adopted on 1 January 1960. This change also adopted leap seconds to simplify future adjustments, a number of proposals have been made to replace UTC with a new system that would eliminate leap seconds, but no consensus has yet been reached. Leap seconds are inserted as necessary to keep UTC within 0.9 seconds of universal time, see the Current number of leap seconds section for the number of leap seconds inserted to date. The official abbreviation for Coordinated Universal Time is UTC and this abbreviation arose from a desire by the International Telecommunication Union and the International Astronomical Union to use the same abbreviation in all languages. English speakers originally proposed CUT, while French speakers proposed TUC, the compromise that emerged was UTC, which conforms to the pattern for the abbreviations of the variants of Universal Time. Time zones around the world are expressed using positive or negative offsets from UTC, the westernmost time zone uses UTC−12, being twelve hours behind UTC, the easternmost time zone, theoretically, uses UTC+12, being twelve hours ahead of UTC. In 1995, the nation of Kiribati moved those of its atolls in the Line Islands from UTC-10 to UTC+14 so that the country would all be on the same day. UTC is used in internet and World Wide Web standards. The Network Time Protocol, designed to synchronise the clocks of computers over the internet, computer servers, online services and other entities that rely on having a universally accepted time use UTC as it is more specific than GMT. If only limited precision is needed, clients can obtain the current UTC from a number of official internet UTC servers, for sub-microsecond precision, clients can obtain the time from satellite signals. UTC is also the standard used in aviation, e. g. for flight plans. Weather forecasts and maps all use UTC to avoid confusion about time zones, the International Space Station also uses UTC as a time standard. Amateur radio operators often schedule their radio contacts in UTC, because transmissions on some frequencies can be picked up by many time zones, UTC is also used in digital tachographs used on large goods vehicles under EU and AETR rules. UTC divides time into days, hours, minutes and seconds, days are conventionally identified using the Gregorian calendar, but Julian day numbers can also be used. Each day contains 24 hours and each hour contains 60 minutes, the number of seconds in a minute is usually 60, but with an occasional leap second, it may be 61 or 59 instead
27.
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
28.
Impact crater
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An impact crater is an approximately circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity impact of a smaller body. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims, Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede and most small moons and asteroids. Where such processes have destroyed most of the original crater topography and this indicates that there should be far more relatively young craters on the planet than have been discovered so far. Note that the rate of impact cratering in the outer Solar System could be different from the inner Solar System, although Earths active surface processes quickly destroy the impact record, about 190 terrestrial impact craters have been identified. They are also found in the stable interior regions of continents. Impact craters are not to be confused with landforms that may appear similar, including calderas, sinkholes, glacial cirques, ring dikes, salt domes, and others. Daniel Barringer was one of the first to identify an impact crater, Meteor Crater in Arizona, in the 1920s, the American geologist Walter H. Bucher studied a number of sites now recognized as impact craters in the United States. He concluded they had created by some great explosive event. However, in 1936, the geologists John D, albritton Jr. revisited Buchers studies and concluded that the craters that he studied were probably formed by impacts. The concept of impact cratering remained more or less speculative until the 1960s, armed with the knowledge of shock-metamorphic features, Carlyle S. By 1970, they had identified more than 50. Although their work was controversial, the American Apollo Moon landings, because the processes of erosion on the Moon are minimal, craters persist almost indefinitely. Since the Earth could be expected to have roughly the same cratering rate as the Moon, Impact cratering involves high velocity collisions between solid objects, typically much greater than the velocity of sound in those objects. Such hyper-velocity impacts produce physical effects such as melting and vaporization that do not occur in familiar sub-sonic collisions. On Earth, ignoring the effects of travel through the atmosphere. The fastest impacts occur at about 72 km/s in the worst case scenario in which an object in a retrograde near-parabolic orbit hits Earth, the median impact velocity on Earth is about 20 km/s. The larger the meteoroid the more of its initial cosmic velocity it preserves, while an object of 9,000 kg maintains about 6% of its original velocity, one of 900,000 kg already preserves about 70%. Extremely large bodies are not slowed by the atmosphere at all, impacts at these high speeds produce shock waves in solid materials, and both impactor and the material impacted are rapidly compressed to high density
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Silicate
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A silicate is a compound containing an anionic silicon compound. The great majority of the silicates are oxides, but hexafluorosilicate, orthosilicate is the anion SiO4−4 or its compounds. Related to orthosilicate are families of anions with the formula 2n−, important members are the cyclic and single chain silicates n and the sheet-forming silicates n. Silicates constitute the majority of Earths crust, as well as the terrestrial planets, rocky moons. Sand, Portland cement, and thousands of minerals are examples of silicates, silicate compounds, including the minerals, consist of silicate anions whose charge is balanced by various cations. Myriad silicate anions can exist, and each can form compounds with many different cations, hence this class of compounds is very large. Both minerals and synthetic materials fit in this class, in the vast majority of silicates, including silicate minerals, the Si occupies a tetrahedral environment, being surrounded by 4 oxygen centres. In these structures, the bonds to silicon conform to the octet rule. These tetrahedra sometimes occur as isolated SiO4−4 centres, but most commonly, commonly the silicate anions are chains, double chains, sheets, and three-dimensional frameworks. All these such species have negligible solubility in water at normal conditions, silicates are well characterized as solids, but are less commonly observed in solution. The anion SiO4−4 is the base of silicic acid, Si4. Instead, solutions of silicates are usually observed as mixtures of condensed, the nature of soluble silicates is relevant to understanding biomineralization and the synthesis of aluminosilicates, such as the industrially important catalysts called zeolites. Although the tetrahedron is the coordination geometry for silicon compounds. A well-known example of such a high number is hexafluorosilicate. Octahedral coordination by 6 oxygen centres is observed, at very high pressure, even SiO2 adopts this geometry in the mineral stishovite, a dense polymorph of silica found in the lower mantle of the Earth. This structure is formed by shock during meteorite impacts. In geology and astronomy, the silicate is used to denote types of rock that consist predominantly of silicate minerals. On Earth, a variety of silicate minerals occur in an even wider range of combinations as a result of the processes that form
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Carbonate
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In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, a polyatomic ion with the formula of CO2−3. The name may mean an ester of carbonic acid, an organic compound containing the carbonate group C2. In geology and mineralogy, the term carbonate can refer both to carbonate minerals and carbonate rock, and both are dominated by the ion, CO2−3. Carbonate minerals are extremely varied and ubiquitous in chemically precipitated sedimentary rock, sodium carbonate and potassium carbonate have been used since antiquity for cleaning and preservation, as well as for the manufacture of glass. Carbonates are widely used in industry, e. g. in iron smelting, as a raw material for Portland cement and lime manufacture, in the composition of ceramic glazes, the carbonate ion is the simplest oxocarbon anion. It consists of one carbon atom surrounded by three oxygen atoms, in a planar arrangement, with D3h molecular symmetry. It has a mass of 60.01 g/mol and carries a total formal charge of −2. It is the base of the hydrogen carbonate ion, HCO−3. The Lewis structure of the ion has two single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen. This structure is incompatible with the symmetry of the ion. This process is called calcination, after calx, the Latin name of quicklime or calcium oxide, CaO, exceptions include lithium, sodium, potassium and ammonium carbonates, as well as many uranium carbonates. In aqueous solution, carbonate, bicarbonate, carbon dioxide, in strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion is prevalent. In more acid conditions, aqueous carbon dioxide, CO2, is the main form, thus sodium carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid. Carbonated water is formed by dissolving CO2 in water under pressure, in living systems an enzyme, carbonic anhydrase, speeds the interconversion of CO2 and carbonic acid. Although the carbonate salts of most metals are insoluble in water, in solution this equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid changes consonant to changing temperature and pressure conditions. In the case of ions with insoluble carbonates, e. g. CaCO3. This is an explanation for the buildup of scale inside pipes caused by hard water, in organic chemistry a carbonate can also refer to a functional group within a larger molecule that contains a carbon atom bound to three oxygen atoms, one of which is double bonded. These compounds are known as organocarbonates or carbonate esters, and have the general formula ROCOOR′
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Smectite
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Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals form in the presence of water and have been important to life and they are important constituents of soils, and have been useful to humans since ancient times in agriculture and manufacturing. Clays form flat hexagonal sheets similar to the micas, Clay minerals are common weathering products and low-temperature hydrothermal alteration products. Clay minerals are common in soils, in fine-grained sedimentary rocks such as shale, mudstone. Clay minerals are usually ultrafine-grained and so may require special techniques for their identification. These methods can be augmented by polarized light microscopy, a traditional technique establishing fundamental occurrences or petrologic relationships. Given the requirement of water, clay minerals are rare in the Solar System, though they occur extensively on Earth where water has interacted with other minerals. Clay minerals have been detected at several locations on Mars including Echus Chasma and Mawrth Vallis and the Memnonia quadrangle, spectrography has confirmed their presence on asteroids including the dwarf planet Ceres and Tempel 1 as well as Jupiters moon Europa. A1,1 clay would consist of one sheet and one octahedral sheet. A2,1 clay consists of an octahedral sheet sandwiched between two sheets, and examples are talc, vermiculite and montmorillonite. Smectite group which includes dioctahedral smectites such as montmorillonite, nontronite and beidellite, in 2013, analytical tests by the Curiosity rover found results consistent with the presence of smectite clay minerals on the planet Mars. Illite group which includes the clay-micas, illite is the only common mineral. Chlorite group includes a variety of similar minerals with considerable chemical variation. Other 2,1 clay types exist such as sepiolite or attapulgite, mixed layer clay variations exist for most of the above groups. Ordering is described as random or regular ordering, and is described by the term reichweite. Literature articles will refer to a R1 ordered illite-smectite, for example and this type would be ordered in an ISISIS fashion. R0 on the other hand describes random ordering, and other advanced ordering types are also found, mixed layer clay minerals which are perfect R1 types often get their own names. R1 ordered chlorite-smectite is known as corrensite, R1 illite-smectite is rectorite, knowledge of the nature of clay became better understood in the 1930s with advancements in x-ray diffraction technology necessary to analyze the molecular nature of clay particles
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Pyrite
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The mineral pyrite, or iron pyrite, also known as fools gold, is an iron sulfide with the chemical formula FeS2. This minerals metallic luster and pale brass-yellow hue give it a resemblance to gold. The color has led to the nicknames brass, brazzle. Pyrite is the most common of the sulfide minerals, the name pyrite is derived from the Greek πυρίτης, of fire or in fire, in turn from πύρ, fire. 1550, the term had become a term for all of the sulfide minerals. Pyrite is usually associated with other sulfides or oxides in quartz veins, sedimentary rock. Despite being nicknamed fools gold, pyrite is sometimes found in association with small quantities of gold, Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37 wt% gold, Pyrite has been used since classical times to manufacture copperas, that is, iron sulfate. Iron pyrite was heaped up and allowed to weather, the acidic runoff from the heap was then boiled with iron to produce iron sulfate. In the 15th century, such leaching began to replace the burning of sulfur as a source of sulfuric acid, by the 19th century, it had become the dominant method. Pyrite remains in use for the production of sulfur dioxide, for use in such applications as the paper industry. Thermal decomposition of pyrite into FeS and elemental sulfur starts at 540 °C, a newer commercial use for pyrite is as the cathode material in Energizer brand non-rechargeable lithium batteries. Pyrite is a material with a band gap of 0.95 eV. During the early years of the 20th century, pyrite was used as a detector in radio receivers. Pyrite detectors occupied a midway point between galena detectors and the more mechanically complicated perikon mineral pairs, Pyrite detectors can be as sensitive as a modern 1N34A germanium diode detector. Pyrite has been proposed as an abundant, inexpensive material in low-cost photovoltaic solar panels, synthetic iron sulfide was used with copper sulfide to create the photovoltaic material. Pyrite is used to make marcasite jewelry, marcasite jewelry, made from small faceted pieces of pyrite, often set in silver, was known since ancient times and was popular in the Victorian era. Marcasite jewelry does not actually contain the mineral marcasite, from the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite is probably best described as Fe2+S22−
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Polycyclic aromatic hydrocarbon
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Polycyclic aromatic hydrocarbons are hydrocarbons—organic compounds containing only carbon and hydrogen—that are composed of multiple aromatic rings. Formally, the class is defined as lacking further branching substituents on these ring structures. Polynuclear aromatic hydrocarbons are a subset of PAHs that have fused aromatic rings, the simplest such chemicals are naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene. PAHs are neutral, nonpolar molecules found in coal and in tar deposits and they are produced as well by incomplete combustion of organic matter. The tricyclic species phenanthrene and anthracene represent the members of the PAHs. Smaller molecules, such as benzene, are not PAHs, PAHs with five or six-membered rings are most common. Those composed only of six-membered rings are called alternant PAHs, which include benzenoid PAHs, the following are examples of PAHs that vary in the number and arrangement of their rings, Examples of PAH compounds PAHs are nonpolar and lipophilic. Larger PAHs are generally insoluble in water, while some PAHs are soluble, the larger members are also poorly soluble in organic solvents as well as lipids. Although PAHs clearly are aromatic compounds, the degree of aromaticity can be different for each ring segment, according to Clars rule for PAHs the resonance structure with the largest number of disjoint aromatic п-sextets—i. e. Benzene-like moieties—is the most important for the characterization of the properties, in contrast, in anthracene the resonance structures have one sextet, which can be at any of the three rings, and the aromaticity spreads out more evenly across the whole molecule. Three Clar structures with two each are present in chrysene. Superposition of these reveals that the aromaticity in the outer rings is greater compared to the inner rings. Polycyclic aromatic hydrocarbons are found in natural sources such as creosote. They can result from the combustion of organic matter. PAHs can also be produced geologically when organic sediments are transformed into fossil fuels such as oil. Wild fires are another notable source, substantially higher outdoor air, soil, and water concentrations of PAHs have been measured in Asia, Africa, and Latin America than in Europe, Australia, and the U. S. /Canada. PAHs are typically found as complex mixtures, most PAHs are insoluble in water, which limits their mobility in the environment. Aqueous solubility of PAHs decreases approximately logarithmically as molecular mass increases, two-ring PAHs, and to a lesser extent three-ring PAHs, dissolve in water, making them more available for biological uptake and degradation
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Ice
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Ice is water frozen into a solid state. Depending on the presence of such as particles of soil or bubbles of air. In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far as away the Oort cloud objects, beyond the Solar System, it occurs as interstellar ice. It falls as snowflakes and hail or occurs as frost, icicles or ice spikes, Ice molecules can exhibit up to sixteen different phases that depend on temperature and pressure. When water is cooled rapidly, up to three different types of ice can form depending on the history of its pressure and temperature. When cooled slowly correlated proton tunneling occurs below 20 K giving rise to macroscopic quantum phenomena, virtually all the ice on Earths surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih with minute traces of cubic ice denoted as ice Ic. The most common phase transition to ice Ih occurs when water is cooled below 0°C at standard atmospheric pressure. It may also be deposited directly by water vapor, as happens in the formation of frost, the transition from ice to water is melting and from ice directly to water vapor is sublimation. Ice is used in a variety of ways, including cooling, winter sports, as a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered a mineral. It possesses a regular crystalline structure based on the molecule of water, an unusual property of ice frozen at atmospheric pressure is that the solid is approximately 8. 3% less dense than liquid water. The density of ice is 0.9167 g/cm3 at 0 °C, liquid water is densest, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid, density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C. When water freezes, it increases in volume and it is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes. The result of this process is that ice floats on liquid water, sufficiently thin ice sheets allow light to pass through while protecting the underside from short-term weather extremes such as wind chill. This creates an environment for bacterial and algal colonies. When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C, during the melting process, the temperature remains constant at 0 °C. While melting, any energy added breaks the bonds between ice molecules. Energy becomes available to increase the thermal energy only after enough hydrogen bonds are broken that the ice can be considered liquid water, the amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion
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81P/Wild
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Comet 81P/Wild, also known as Wild 2, is a comet named after Swiss astronomer Paul Wild, who discovered it on January 6,1978, using a 40-cm Schmidt telescope at Zimmerwald, Switzerland. For most of its 4.5 billion-year lifetime, Wild 2 probably had a more distant, in September 1974, it passed within one million kilometers of the planet Jupiter, the strong gravitational pull of which perturbed the comets orbit and brought it into the inner Solar System. Its orbital period changed from 43 years to about 6 years, and its perihelion is now about 1.59 astronomical unit. Dimensions,5.5 km ×4.0 km ×3.3 km Density,0.6 g/cm3 Mass,2.3 kg ×1013 NASAs Stardust Mission launched a spacecraft, named Stardust, on February 7,1999. It flew by Wild 2 on January 2,2004, and collected samples from the comets coma. 72 close-up shots were taken of Wild 2 by Stardust and they revealed a surface riddled with flat-bottomed depressions, with sheer walls and other features that range from very small to up to 2 kilometres across. These features are believed to be caused by impact craters or gas vents, during Stardusts flyby, at least 10 gas vents were active. The comet itself has a diameter of 5 kilometres, Stardusts sample return canister was reported to be in excellent condition when it landed in Utah, on January 15,2006. A NASA team analyzed the particle capture cells and removed individual grains of comet and interstellar dust, NASA is collaborating with The Planetary Society who will run a project called Stardust@Home, using volunteers to help locate particles on the Stardust Interstellar Dust Collector. As of 2006, the composition of the dust has contained a range of organic compounds. Indigenous aliphatic hydrocarbons were found with longer lengths than those observed in the diffuse interstellar medium. No hydrous silicates or carbonate minerals were detected, which suggests a lack of processing of Wild 2 dust. Very few pure carbon particles were found in the samples returned, a substantial amount of crystalline silicates such as olivine, anorthite and diopside were found, materials only formed at high temperature. This is consistent with observations of crystalline silicates both in cometary tails and in circumstellar disks at large distances from the star. Possible explanations for this high temperature material at large distances from Sun were summarised before the Stardust sample return mission by van Boekel et al, both in the Solar System and in circumstellar disks crystalline silicates are found at large distances from the star. The origin of these silicates is a matter of debate, the crystals in these regions may have been transported outward through the disk or in an outward-flowing wind. An alternative source of crystalline silicates in the outer disk regions is in situ annealing, a third way to produce crystalline silicates is the collisional destruction of large parent bodies in which secondary processing has taken place. We can use the mineralogy of the dust to derive information about the nature of the primary and/or secondary processes the small-grain population has undergone
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Volatiles
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In planetary science, volatiles are the group of chemical elements and chemical compounds with low boiling points that are associated with a planets or moons crust or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, methane, in astrogeology, these compounds, in their solid state, often comprise large proportions of the crusts of moons and dwarf planets. In contrast with volatiles, elements and compounds with high boiling points are known as refractory substances, the terms gas and ice in this context can apply to compounds that may be solids, liquids or gases. The Moon is very low in volatiles, its crust contains oxygen chemically bound into the rocks, in igneous petrology the term more specifically refers to the volatile components of magma that affect the appearance and explosivity of volcanoes. Volatiles in a magma with a high viscosity, generally felsic with a silica content. Volatiles in a magma with a low viscosity, generally mafic with a silica content, tend to vent. Some volcanic eruptions are explosive because the mixing water and magma reaching the surface, releases energy suddenly. Moreover, in cases, the eruption is caused by volatiles dissolved in the magma. Approaching the surface, pressure decreases and the volatiles evolve creating bubbles that circulate in the liquid, the bubbles are connected together forming a network. This especially increments the fragmentation into small drops or spray or coagulate clots in gas, generally, 95-99% of magma is liquid rock. However, the percentage of gas present, represents a very large volume when it expands on reaching atmospheric pressure. Gas is a preponderant part in a system because it generates explosive eruptions. Magma in the mantle and lower crust have a lot of volatiles within and water, also they leak hydrogen sulfide and sulfur dioxide. Sulfur dioxide is usually possible to find in basaltic and rhyolite rocks, volcanoes also release a high amount of hydrogen chloride and hydrogen fluoride as volatiles. There are three factors that effect the dispersion of volatiles in magma, confining pressure, composition of magma. Pressure and composition are the most important parameters, to understand how the magma behaves rising the surface, the role of solubility within the magma must be known. An empirical law has used for different magma-volatiles combination. For instance, for water in magma the equation is n=0.1078 P where n is the amount of dissolved gas as weight percentage, the value changes for example for water in rhyolite where n=0.4111 P and for the carbon dioxide is n=0.0023 P
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Sublimation (phase transition)
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Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Sublimation is a process that occurs at temperatures and pressures below a substances triple point in its phase diagram. The reverse process of sublimation is deposition or desublimation, in which a substance directly from a gas to a solid phase. Sublimation has also used as a generic term to describe a solid-to-gas transition followed by a gas-to-solid transition. At normal pressures, most chemical compounds and elements possess three different states at different temperatures, in these cases, the transition from the solid to the gaseous state requires an intermediate liquid state. The pressure referred to is the pressure of the substance. So, all solids that possess an appreciable vapor pressure at a temperature usually can sublimate in air. The term sublimation refers to a change of state and is not used to describe transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of ammonium chloride into hydrogen chloride and ammonia is not sublimation. Similarly the combustion of candles, containing paraffin wax, to carbon dioxide and water vapor is not sublimation, sublimation requires additional energy and is an endothermic change. The enthalpy of sublimation can be calculated by adding the enthalpy of fusion, solid carbon dioxide sublimes everywhere along the line below the triple point, whereas its melting into liquid CO2 can occur only along the line at pressures and temperatures above the triple point. Snow and ice sublime, although more slowly, at temperatures below the freezing/melting point temperature line at 0 °C for most pressures, in freeze-drying, the material to be dehydrated is frozen and its water is allowed to sublime under reduced pressure or vacuum. The loss of snow from a snowfield during a spell is often caused by sunshine acting directly on the upper layers of the snow. Ablation is a process that includes sublimation and erosive wear of glacier ice, naphthalene, an organic compound commonly found in pesticide such as mothball also sublimes. It sublimes easily because it is made of molecules and has van der Waals intermolecular forces. Naphthalene is a solid that sublimes at atmospheric temperature with the sublimation point at around 80˚C or 176˚F. At low temperature, its pressure is high enough,1 mmHg at 53˚C. On the cool surface, the sublimated vapour will be solidified to form a needle-like crystal, iodine produces fumes on gentle heating
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Dwarf planet
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A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. The International Astronomical Union currently recognizes five dwarf planets, Ceres, Pluto, Haumea, Makemake, another hundred or so known objects in the Solar System are suspected to be dwarf planets. Individual astronomers recognize several of these, and in August 2011 Mike Brown published a list of 390 candidate objects, Stern states that there are more than a dozen known dwarf planets. Only two of these bodies, Ceres and Pluto, have observed in enough detail to demonstrate that they actually fit the IAUs definition. The IAU accepted Eris as a dwarf planet because it is more massive than Pluto and they subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 are to be named under the assumption that they are dwarf planets. The classification of bodies in other systems with the characteristics of dwarf planets has not been addressed. Starting in 1801, astronomers discovered Ceres and other bodies between Mars and Jupiter which were for some decades considered to be planets. Between then and around 1851, when the number of planets had reached 23, astronomers started using the asteroid for the smaller bodies. With the discovery of Pluto in 1930, most astronomers considered the Solar System to have nine planets and it was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet. Although it was more than ten times as massive as the largest object in the asteroid belt, Ceres. In the 1990s, astronomers began to find objects in the region of space as Pluto. Many of these shared several of Plutos key orbital characteristics, and Pluto started being seen as the largest member of a new class of objects and this led some astronomers to stop referring to Pluto as a planet. Several terms, including subplanet and planetoid, started to be used for the now known as dwarf planets. By 2005, three trans-Neptunian objects comparable in size to Pluto had been reported and it became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified. Astronomers were also confident that more objects as large as Pluto would be discovered, Eris was discovered in January 2005, it was thought to be slightly larger than Pluto, and some reports informally referred to it as the tenth planet. As a consequence, the became a matter of intense debate during the IAU General Assembly in August 2006. The IAUs initial draft proposal included Charon, Eris, and Ceres in the list of planets, dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, because they have not cleared their orbits. The IAUs final Resolution 5A preserved this three-category system for the bodies orbiting the Sun
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Ceres (dwarf planet)
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Ceres is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter. Its diameter is approximately 945 kilometers, making it the largest of the planets within the orbit of Neptune. The 33rd-largest known body in the Solar System, it is the dwarf planet within the orbit of Neptune. Composed of rock and ice, Ceres is estimated to approximately one third of the mass of the entire asteroid belt. Ceres is the object in the asteroid belt known to be rounded by its own gravity. From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, Ceres was the first asteroid discovered, by Giuseppe Piazzi at Palermo on 1 January 1801. It was originally considered a planet, but was reclassified as an asteroid in the 1850s after many other objects in similar orbits were discovered. Ceres appears to be differentiated into a core and icy mantle. The surface is probably a mixture of ice and various hydrated minerals such as carbonates. In January 2014, emissions of water vapor were detected from several regions of Ceres and this was unexpected, because large bodies in the asteroid belt typically do not emit vapor, a hallmark of comets. The robotic NASA spacecraft Dawn entered orbit around Ceres on 6 March 2015, pictures with a resolution previously unattained were taken during imaging sessions starting in January 2015 as Dawn approached Ceres, showing a cratered surface. Two distinct bright spots inside a crater were seen in a 19 February 2015 image, on 11 May 2015, NASA released a higher-resolution image showing that, instead of one or two spots, there are actually several. In October 2015, NASA released a true portrait of Ceres made by Dawn. In February 2017, organics were reported to have been detected on Ceres in Ernutet crater, Johann Elert Bode, in 1772, first suggested that an undiscovered planet could exist between the orbits of Mars and Jupiter. Kepler had already noticed the gap between Mars and Jupiter in 1596, the pattern predicted that the missing planet ought to have an orbit with a semi-major axis near 2.8 astronomical units. Although they did not discover Ceres, they found several large asteroids. One of the selected for the search was Giuseppe Piazzi. Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801 and he was searching for the 87th of the Catalogue of the Zodiacal stars of Mr la Caille, but found that it was preceded by another
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Gas giant
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A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System, for this reason, Uranus and Neptune are now often classified in the separate category of ice giants. Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of the mass and they are thought to consist of an outer layer of molecular hydrogen surrounding a layer of liquid metallic hydrogen, with probably a molten rocky core. The outermost portion of their hydrogen atmosphere is characterized by layers of visible clouds that are mostly composed of water. The layer of metallic hydrogen makes up the bulk of each planet, the gas giants cores are thought to consist of heavier elements at such high temperatures and pressures that their properties are poorly understood. The defining differences between a very low-mass brown dwarf and a gas giant are debated, one school of thought is based on formation, the other, on the physics of the interior. Part of the debate concerns whether brown dwarfs must, by definition, have experienced nuclear fusion at some point in their history, the term gas giant was coined in 1952 by the science fiction writer James Blish and was originally used to refer to all giant planets. Arguably it is something of a misnomer, because throughout most of the volume of all giant planets the pressure is so high that matter is not in gaseous form. Other than solids in the core and the layers of the atmosphere, all matter is above the critical point. In the outer Solar System, hydrogen and helium are referred to as gases, water, methane, and ammonia as ices, and silicates and metals as rock. Because Uranus and Neptune are primarily composed of, in this terminology, ices, not gas, they are referred to as ice giants. Jupiter and Saturn are both class I, hot Jupiters are class IV or V. A cold hydrogen-rich gas giant more massive than Jupiter but less than about 500 M⊕ will only be larger in volume than Jupiter. For masses above 500 M⊕, gravity will cause the planet to shrink, kelvin–Helmholtz heating can cause a gas giant to radiate more energy than it receives from its host star. Although the words gas and giant are often combined, hydrogen planets need not be as large as the gas giants from the Solar System. However, smaller gas planets and planets closer to their star will lose atmospheric mass more quickly via hydrodynamic escape than larger planets and planets farther out. The smallest known extrasolar planet that is likely a gas planet is Kepler-138d, a low-mass gas planet can still have a radius resembling that of a gas giant if it has the right temperature. List of gravitationally rounded objects of the Solar System List of planet types
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Mars
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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
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The Planetary Society
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The Planetary Society is an American internationally active non-governmental, nonprofit foundation. It is involved in research, public outreach, and political advocacy for engineering projects related to astronomy, planetary science, and space exploration. It was founded in 1980 by Carl Sagan, Bruce Murray, and Louis Friedman, the Society is dedicated to the exploration of the Solar System, the search for near-Earth objects, and the search for extraterrestrial life. The societys mission is stated as, To empower the citizens to advance space science. The Planetary Society is also an advocate for space funding. They actively lobby Congress and engage their membership in the United States to write, in addition to public outreach, The Planetary Society also sponsors novel and innovative projects that will seed further exploration. Two of the highest profile programs are Lightsail and LIFE, Lightsail is a series of three solar sail experiments. LightSail-1 is expected to piggyback on a future NASA mission, in June 2005, the Society launched the Cosmos 1 craft to test the feasibility of solar sailing, but the rocket failed shortly after liftoff. LIFE was a program designed to test the ability of microorganisms to survive in space. The first phase flew on STS-134, shuttle Endeavors final flight in 2011, the second phase rode on Russias Fobos-Grunt mission, which attempted to go to Mars moon Phobos and back but failed to escape earth orbit. The Planetary Society was founded in 1980 by Carl Sagan, Bruce Murray, and Louis Friedman as a champion of support of space exploration. In addition to its affairs, the Society has created a number of space related projects. The SETI program began with Paul Horowitzs Suitcase SETI and has grown to encompass searches in radio, sETI@home, the largest distributed computing experiment on Earth, is perhaps the Societys best-known SETI project. The Board has a chairman, President, and Vice President and an Executive Committee, nominations are sought and considered periodically from a variety of sources, including from members of the Board and Advisory Council, Society Members, staff, and experts in the space community. On June 7,2010, the Society announced that famed American science educator Bill Nye would become the new director of the society. All of these projects are funded by the Societys members and donors, some projects include, A members donation of $4.2 million in 2014 will be used by the Society to further their research into solar sails and asteroid tracking. It went from bimonthly to quarterly with the June 2011 issue, the Planetary Society also produces Planetary Radio, a weekly 30-minute radio program and podcast hosted and produced by Mat Kaplan
