1.
John Tebbutt
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John Tebbutt was an Australian astronomer, famous for discovering the Great Comet of 1861. Tebbutt was born at Windsor, New South Wales, the son of John Tebbutt. His grandfather, John Tebbutt, was one of the settlers in Australia. In 1845 Tebbutts father purchased a tract of land at the end of the town of Windsor known as the peninsula. In 1853 John Tebutt purchased a sextant and using this along with a marine telescope. About nine years later, on 13 May 1861, Tebbutt discovered the 1861 comet, there was no means then of telegraphing the intelligence to England where it became visible on 29 June. Tebbutt was acknowledged as the first discoverer of this comet, and he continued the publication of these records at intervals for more than 30 years. He contributed to scientific journals, and made an immense number of contributions to the Australian press. He published in 1887 History and description of Mr. Tebbutts observatory, Windsor, New South Wales, a branch of the British Astronomical Association was established at Sydney in 1895 and Tebbutt was elected its first president. He died at Windsor on 29 November 1916, the year after his death his son delivered John Tebbutt’s working library and manuscripts to the State Library of New South Wales. The John Tebbutt Memorial Collection is made up of 3,676 printed volumes,117 volumes of manuscripts and 235 pamphlets and he was commemorated on the reverse side of the Australian one hundred-dollar note
2.
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
3.
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
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.
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
6.
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
7.
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
8.
Naked eye
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Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered naked, in astronomy, the naked eye may be used to observe events that can be viewed without equipment, such as an astronomical conjunction, the passage of a comet, or a meteor shower. Sky lore and various tests demonstrate a wealth of phenomena that can be seen with the unaided eye. The basic accuracies of the eye are, Quick autofocus from distances of 25 cm to 50 cm to infinity. Angular resolution, about 1 arcminute, approximately 0. 02° or 0.0003 radians, field of view, simultaneous visual perception in an area of about 160° × 175°. Faint stars up to +8 magnitude under a dark sky. Photometry to ±10% or 1% of intensity – in a range between night and day of 1,10,000,000,000, symmetries of 10–20, see the measurements of Tycho Brahe and the Egyptians. Even a few hundred kilometers away from an area where the sky can appear to be very dark. For most people, these are likely to be the best observing conditions within their reach, under such typical dark sky conditions, the naked eye can see stars with an apparent magnitude up to +6m. Under perfect dark sky conditions where all light pollution is absent, the angular resolution of the naked eye is about 1′, however, some people have sharper vision than that. There is anecdotal evidence that people had seen the Galilean moons of Jupiter before telescopes were invented, Uranus, when discovered in 1781, was the first planet discovered using technology rather than being spotted by the naked eye. In practice, the extinction and dust reduces this number somewhat. In the center of a city, where the limiting magnitude due to extreme amounts of light pollution can be +4m or less. Colors can be seen but this is limited by the fact that the eye uses rods instead of cones to view fainter stars, the visibility of diffuse objects such as star clusters and galaxies is much more strongly affected by light pollution than is that of planets and stars. Under typical dark conditions only a few objects are visible. The Triangulum Galaxy is a difficult averted vision object and only visible at all if it is higher than 50° in the sky, the globular clusters M3 in Canes Venatici and M92 in Hercules are also visible with the naked eye under such conditions. Under really dark sky conditions, however, M33 is easy to see, many other Messier objects are also visible under such conditions. The most distant objects that have seen by the naked eye are nearby bright galaxies such as Centaurus A, Bodes Galaxy, Sculptor Galaxy
9.
Great comet
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A great comet is a comet that becomes exceptionally bright. Great comets are rare, on average, only one will appear in a decade, although comets are officially named after their discoverers, great comets are sometimes also referred to by the year in which they appeared great, using the formulation The Great Comet of. The vast majority of comets are never enough to be seen by the naked eye. However, occasionally a comet may brighten to naked eye visibility, the requirements for this to occur are, a large and active nucleus, a close approach to the Sun, and a close approach to the Earth. A comet fulfilling all three of these criteria will certainly be spectacular, sometimes, a comet failing on one criterion will still be extremely impressive. For example, Comet Hale–Bopp had a large and active nucleus. Equally, Comet Hyakutake was a small comet, but appeared bright because it passed extremely close to the Earth. Cometary nuclei vary in size from a few hundreds of metres across or less to many kilometres across, when they approach the Sun, large amounts of gas and dust are ejected by cometary nuclei, due to solar heating. A crucial factor in how bright a comet becomes is how large, the sudden brightening of comet 17P/Holmes in 2007 showed the importance of the activity of the nucleus in the comets brightness. On October 23–24,2007, the comet suffered a sudden outburst which caused it to brighten by factor of about half a million. It unexpectedly brightened from an apparent magnitude of about 17 to about 2.8 in a period of only 42 hours, all these temporarily made comet 17P the largest object in the Solar System although its nucleus is estimated to be only about 3.4 km in diameter. The brightness of a simple reflective body varies with the square of its distance from the Sun. That is, if a distance from the Sun is halved. However, comets behave differently, due to their ejection of large amounts of gas which then also reflect sunlight. Their brightness varies roughly as the cube of their distance from the Sun, meaning that if a comets distance from the Sun is halved. This means that the brightness of a comet depends significantly on its distance from the Sun. For most comets, the perihelion of their orbit lies outside the Earths orbit, any comet approaching the Sun to within 0.5 AU or less may have a chance of becoming a great comet. For a comet to become spectacular, it needs to pass close to the Earth
10.
Windsor, New South Wales
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Windsor is a town lying North-West of Sydney, New South Wales, Australia. Windsor is located in the government area of the City of Hawkesbury. It sits on the Hawkesbury River, on the outskirts of the Sydney metropolitan area. At the 2011 census, Windsor had a population of 1,803, Windsor is the third-oldest place of British settlement on the Australian continent. Settlement at the location was first established about 1791, near the head of navigation on the Hawkesbury River, the area was originally called Green Hills, but renamed Windsor. While in Windsor, Macquarie ordered the main institutions of organised settlement to be erected, such as a church, school-house, gaol, of these new buildings, the most outstanding was Francis Greenways Saint Matthews Anglican Church, for which Macquarie himself chose the site. Samuel Marsden, principal chaplain of the colony, consecrated the church on 8 December 1822, in 1813 a report was given to Governor Macquarie from Earl Bathurst detailing a proposed invasion of the Hawkesbury River by France. This planned invasion that did not eventuate, targeted the Windsor granary in order to cut off supply to Sydney and it was known as the bread basket, ensuring the survival of the starving colony. The extensive agriculture caused major silting in the Hawkesbury River, by the 1890s the river had become so blocked with silt, by then the railway, in 1864, and the road, in 1814, had been built. On 1 January 1803 Daniel Egan was born in Windsor and he went on to become Mayor of Sydney in 1853. Many of the oldest surviving European buildings in Australia are located at Windsor, the following buildings are listed on the Register of the National Estate. 1835–1880 George Street Inn Group, George Street, c, 1840–1875 Thompson Square Precinct and Bridge Street Buildings, including Hawkesbury Museum, c.4 persons per kilometre. As of 2008, Windsor had an unemployment rate of 3. 4% with 59. 5% of the receiving the Newstart Allowance for a period of longer than 365 days. The average taxable income of Windsor was $50,064 as of 2007,3,719 working individuals received a total of $186. 2m of taxable income. As of December 2016, Windsor has a house price of $650,101. Floods are a concern in Windsor. Its proximity to the Hawkesbury River has resulted in disastrous floods. A horseshoe on the wall of the Macquarie Arms pub marks the level the flood peaked at in 1867
11.
Australia
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Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the worlds sixth-largest country by total area, the neighbouring countries are Papua New Guinea, Indonesia and East Timor to the north, the Solomon Islands and Vanuatu to the north-east, and New Zealand to the south-east. Australias capital is Canberra, and its largest urban area is Sydney, for about 50,000 years before the first British settlement in the late 18th century, Australia was inhabited by indigenous Australians, who spoke languages classifiable into roughly 250 groups. The population grew steadily in subsequent decades, and by the 1850s most of the continent had been explored, on 1 January 1901, the six colonies federated, forming the Commonwealth of Australia. Australia has since maintained a liberal democratic political system that functions as a federal parliamentary constitutional monarchy comprising six states. The population of 24 million is highly urbanised and heavily concentrated on the eastern seaboard, Australia has the worlds 13th-largest economy and ninth-highest per capita income. With the second-highest human development index globally, the country highly in quality of life, health, education, economic freedom. The name Australia is derived from the Latin Terra Australis a name used for putative lands in the southern hemisphere since ancient times, the Dutch adjectival form Australische was used in a Dutch book in Batavia in 1638, to refer to the newly discovered lands to the south. On 12 December 1817, Macquarie recommended to the Colonial Office that it be formally adopted, in 1824, the Admiralty agreed that the continent should be known officially as Australia. The first official published use of the term Australia came with the 1830 publication of The Australia Directory and these first inhabitants may have been ancestors of modern Indigenous Australians. The Torres Strait Islanders, ethnically Melanesian, were originally horticulturists, the northern coasts and waters of Australia were visited sporadically by fishermen from Maritime Southeast Asia. The first recorded European sighting of the Australian mainland, and the first recorded European landfall on the Australian continent, are attributed to the Dutch. The first ship and crew to chart the Australian coast and meet with Aboriginal people was the Duyfken captained by Dutch navigator, Willem Janszoon. He sighted the coast of Cape York Peninsula in early 1606, the Dutch charted the whole of the western and northern coastlines and named the island continent New Holland during the 17th century, but made no attempt at settlement. William Dampier, an English explorer and privateer, landed on the north-west coast of New Holland in 1688, in 1770, James Cook sailed along and mapped the east coast, which he named New South Wales and claimed for Great Britain. The first settlement led to the foundation of Sydney, and the exploration, a British settlement was established in Van Diemens Land, now known as Tasmania, in 1803, and it became a separate colony in 1825. The United Kingdom formally claimed the part of Western Australia in 1828. Separate colonies were carved from parts of New South Wales, South Australia in 1836, Victoria in 1851, the Northern Territory was founded in 1911 when it was excised from South Australia
12.
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
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.
Kilometre
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The kilometre or kilometer is a unit of length in the metric system, equal to one thousand metres. K is occasionally used in some English-speaking countries as an alternative for the kilometre in colloquial writing. A slang term for the kilometre in the US military is klick, there are two common pronunciations for the word. It is generally preferred by the British Broadcasting Corporation and the Australian Broadcasting Corporation, many scientists and other users, particularly in countries where the metric system is not widely used, use the pronunciation with stress on the second syllable. The latter pronunciation follows the pattern used for the names of measuring instruments. The problem with this reasoning, however, is that the meter in those usages refers to a measuring device. The contrast is more obvious in countries using the British rather than American spelling of the word metre. When Australia introduced the system in 1975, the first pronunciation was declared official by the governments Metric Conversion Board. However, the Australian prime minister at the time, Gough Whitlam, by the 8 May 1790 decree, the Constituent assembly ordered the French Academy of Sciences to develop a new measurement system. In August 1793, the French National Convention decreed the metre as the length measurement system in the French Republic. The first name of the kilometre was Millaire, although the metre was formally defined in 1799, the myriametre was preferred to the kilometre for everyday use. The term myriamètre appeared a number of times in the text of Develeys book Physique dEmile, ou, Principes de la de la nature. French maps published in 1835 had scales showing myriametres and lieues de Poste, the Dutch, on the other hand, adopted the kilometre in 1817 but gave it the local name of the mijl. It was only in 1867 that the term became the only official unit of measure in the Netherlands to represent 1000 metres. In the US, the National Highway System Designation Act of 1995 prohibits the use of highway funds to convert existing signs or purchase new signs with metric units. Although the State DOTs had the option of using metric measurements or dual units, all of them abandoned metric measurements, the Manual on Uniform Traffic Control Devices since 2000 is published in both metric and American Customary Units. Some sporting disciplines feature 1000 m races in major events, but in other disciplines, even though records are catalogued
15.
Mile
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The mile is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959. The Romans divided their mile into 5,000 feet but the importance of furlongs in pre-modern England meant that the statute mile was made equivalent to 8 furlongs or 5,280 feet in 1593. This form of the mile then spread to the British-colonized nations who continue to employ the mile, the US Geological Survey now employs the metre for official purposes but legacy data from its 1927 geodetic datum has meant that a separate US survey mile continues to see some use. Derived units such as miles per hour and miles per gallon, however, continue to be abbreviated as mph, mpg. The modern English word mile derives from Middle English myl and Old English mīl, the present international mile is usually what is understood by the unqualified term mile. When this distance needs to be distinguished from the nautical mile, in British English, the statute mile may refer to the present international miles or to any other form of English mile since the 1593 Act of Parliament which set it as a distance of 1,760 yards. Under American law, however, the statute mile refers to the US survey mile, the mile has been variously abbreviated—with and without a trailing period—as m, M, ml, and mi. The American National Institute of Standards and Technology now uses and recommends mi in order to avoid confusion with the SI metre and millilitre. Derived units such as miles per hour and miles per gallon, however, continue to be abbreviated in the United States, United Kingdom, the BBC style holds that There is no acceptable abbreviation for ‘miles’ and so it should be spelt out when used in describing areas. The Roman mile consisted of a thousand paces as measured by every other step—as in the distance of the left foot hitting the ground 1,000 times. The ancient Romans, marching their armies through uncharted territory, would push a carved stick in the ground after each 1000 paces. Well-fed and harshly driven Roman legionaries in good weather thus created longer miles, the distance was indirectly standardised by Agrippas establishment of a standard Roman foot in 29 BC, and the definition of a pace as 5 feet. An Imperial Roman mile thus denoted 5,000 Roman feet, surveyors and specialized equipment such as the decempeda and dioptra then spread its use. In modern times, Agrippas Imperial Roman mile was empirically estimated to have been about 1,481 metres in length, in Hellenic areas of the Empire, the Roman mile was used beside the native Greek units as equivalent to 8 stadia of 600 Greek feet. The mílion continued to be used as a Byzantine unit and was used as the name of the zero mile marker for the Byzantine Empire. The Roman mile also spread throughout Europe, with its local variations giving rise to the different units below, also arising from the Roman mile is the milestone. All roads radiated out from the Roman Forum throughout the Empire –50,000 miles of stone-paved roads, at every mile was placed a shaped stone, on which was carved a Roman numeral, indicating the number of miles from the center of Rome – the Forum. Hence, one knew how far one was from Rome
16.
Comet tail
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A comet tail—and coma—are features visible in comets when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the materials within the comet to vaporize and stream out of the nucleus. Separate tails are formed of dust and gases, becoming visible through different phenomena, the dust reflects sunlight directly, most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye. In the outer Solar System, comets remain frozen and are difficult or impossible to detect from Earth due to their small size. As a comet approaches the inner Solar System, solar radiation causes the materials within the comet to vaporize and stream out of the nucleus. The streams of dust and gas each form their own distinct tail, the tail of dust is left behind in the comets orbit in such a manner that it often forms a curved tail called the antitail, only when it seems that it is directed towards the Sun. At the same time, the ion tail, made of gases, the ion tail follows the magnetic field lines rather than an orbital trajectory. Parallax viewing from the Earth may sometimes mean the tails appear to point in opposite directions. While the solid nucleus of comets is generally less than 50 km across, the coma may be larger than the Sun, the Ulysses spacecraft made an unexpected pass through the tail of the comet C/2006 P1, on February 3,2007. Evidence of the encounter was published in the October 1,2007 issue of the Astrophysical Journal, the observation of antitails contributed significantly to the discovery of solar wind. The ion tail is the result of ultraviolet radiation ejecting electrons off particles in the coma, once the particles have been ionised, they form a plasma which in turn induces a magnetosphere around the comet. The comet and its magnetic field form an obstacle to outward flowing solar wind particles. The comet is supersonic relative to the wind, so a bow shock is formed upstream of the comet. In this bow shock, large concentrations of cometary ions congregate, the field lines drape around the comet forming the ion tail. If the ion tail loading is sufficient, then the field lines are squeezed together to the point where, at some distance along the ion tail. This leads to a disconnection event. This has been observed on a number of occasions, notable among which was on the 20th, april 2007 when the ion tail of comet Encke was completely severed as the comet passed through a coronal mass ejection. This event was observed by the STEREO spacecraft, a disconnection event was also seen with C/2009 R1 on May 26,2010
17.
Forward scatter
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The scattering process may be polarization-sensitive, i. e. incident waves that are identical in every respect but their polarization may be scattered differently. Comets studied forward-scattering in visible-thermal photometry include C/1927 X1, C/1975 V1, comets studied forward-scattering in SOHO non-thermal C3 coronograph photometry include 96P/Machholz and C/2004 F4. The brightness of the great comets C/2006 P1 and Comet Skjellerup–Maristany near perihelion were enhanced by forward scattering and this article incorporates public domain material from the General Services Administration document Federal Standard 1037C. Cassinis Views of Saturns Rings Light Scattering Demonstration
18.
Johann Friedrich Julius Schmidt
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Johann Friedrich Julius Schmidt was a German astronomer and geophysicist. As a student at a gymnasium in Hamburg, he impressed with his sense of form and drawing abilities and demonstrated a strong interest in science. When he was 14, he came into the possession of a copy of Selenotopographische Fragmente by Johann Hieronymus Schröter, and this influenced a lifelong interest in selenography, the study of the Moon. He went to school in Hamburg and visited Altona Observatory, where he acquainted with the well-known map of the Moon made by Wilhelm Beer. Rümker taught him the fundamentals of astronomical observation, in 1845, he obtained a position as an assistant at the private Benzenberg observatory in Bilk near Düsseldorf, but a year later joined the Bonn Observatory under Friedrich Wilhelm Argelander. In 1853 he became director of Baron von Unkrechtsbergs private observatory at Olmütz, in 1858, he became director of the new Athens Observatory, where the clear skies were very suited to astronomical observation, and where he spent the rest of his career. He spent most of his career since his youth making drawings of the Moon, in 1866 he made the astonishing claim that Linné crater had considerably changed its appearance, which began a controversy that continued for many decades. Coming from such a careful observer, the claim carried some weight, however. By 1868 his map of the Moon was almost ready, although he did not put the finishing touches to it until 1874 and this was the first map of the Moon to surpass the celebrated map of Beer and Mädler. On 24 November 1876 he discovered Nova Cygni, also known as Q Cygni, in 1878, Schmidt also edited and published all 25 sections of a moon map by Wilhelm Gotthelf Lohrmann. Lohrmann had completed his map in 1836 but had died in 1840, Schmidt was awarded the Valz Prize from the French Academy of Sciences in recognition of this selenographic work. He also studied vulcanism and seismic phenomena on Earth, sometimes at the risk of his life and he was a pioneer in using the anaeroid barometer for measuring altitude. He published a work on the geography of Greece. Other interests were the nature of comets and the brightness. He received a doctorate from Bonn in 1868. When he died, the King and Queen of Greece attended the funeral oration at his observatory, the crater Schmidt on the Moon is jointly named for him and two other people of the same last name. The years of Julius Schmidt in the Athens Observatory from the National Observatory of Athens Astronomische Nachrichten, v.108, monthly Notices of the Royal Anstronomical Society, v.45, pp. 211-212. The Observatory, v.7, pp. 118-119
19.
National Observatory of Athens
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The National Observatory of Athens is a research institute in Athens, Greece. Around 1840, the benefactor, Baron Georgios Sinas, ambassador in Vienna. He took advice from his friend, the Austrian ambassador in Athens Prokesch-Osten, Bouris became the first director of Athens Observatory, and was also involved in the construction of its first building. The cross-like neoclassic building has its sides oriented toward the four directions of the horizon, there is a small dome for a telescope in the center of the construction. The building was completed in 1846, using the donation Bouris ordered and installed the following instruments in the new building,6.2 refractor Ploessl 3. Present were the King of Greece Otto, members of the Government, a large crowd of people fills up the vicinity of the place selected for the Observatory, a location on the hill of Nymphs at Thiseio, facing the Acropolis. Following the panegyric speech by professor Bouris, the stone is set under music sounds. In 1855 Bouris became ill and moved back to retire in Vienna, prof. Ioannis G. Papadakis, full Professor of Mathematics, since 17 August 1854, at the University of Athens was chosen as an interim Director. Utilizing the Sinas family donation, Johann Friedrich Julius Schmidt took care of the instruments repairing, soon he started to observe the Sun, Moon, planets, comets and variable stars. He enriched the Observatorys library with many books and journals. Some of them were donated by other European observatories, Schmidt also started the editing of Publications of the Observatory of Athens. During the 25 years of his work in the Athens Observatory, he performed more than 70,000 observations of stars and discovered few periodic variables. Most of the results were published in the journal Astronomische Nachrichten, for many years, J. Schmidt studied the planets Mars and Jupiter and drew the changes on their surfaces. He observed the comet of the 1860 and two years later discovered a periodic comet. The clear sky allowed him to make observations of meteors. He also had the opportunity to observe a number of Solar eclipses, the Topographical Chart of the Moon published in Berlin, is perhaps his most brilliant work. In an area of two meters diameter, consisting of 25 parts and representing the surface of the Moon. Significant is also his study of the crater Linne showing apparent morphological changes, Julius Schmidt reorganized the meteorological service of the Observatory of Athens
20.
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
21.
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
22.
Eris (dwarf planet)
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Eris is the most massive and second-largest dwarf planet known in the Solar System. It is also the known body directly orbiting the Sun. It is measured to be 2,326 ±12 kilometers in diameter, Eris is 27% more massive than dwarf planet Pluto, though Pluto is slightly larger by volume. Eris mass is about 0. 27% of the Earths mass, Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity was verified later that year. It is an object and a member of a high-eccentricity population known as the scattered disk. It has one moon, Dysnomia. As of February 2016, its distance from the Sun is 96.3 astronomical units, because Eris appeared to be larger than Pluto, NASA initially described it as the Solar Systems tenth planet. This, along with the prospect of other objects of similar size being discovered in the future, motivated the International Astronomical Union to define the term planet for the first time. Observations of an occultation by Eris in 2010 showed that its diameter was 2,326 ±12 kilometers, very slightly less than Pluto. Eris was discovered by the team of Mike Brown, Chad Trujillo, the discovery was announced on July 29,2005, the same day as Makemake and two days after Haumea, due in part to events that would later lead to controversy about Haumea. Routine observations were taken by the team on October 21,2003, in January 2005, the re-analysis revealed Eriss slow motion against the background stars. Follow-up observations were carried out to make a preliminary determination of Eriss orbit. More observations released in October 2005 revealed that Eris has a moon, observations of Dysnomias orbit permitted scientists to determine the mass of Eris, which in June 2007 they calculated to be ×1022 kg, 27%±2% greater than Plutos. Eris is named after the Greek goddess Eris, a personification of strife, the regular adjectival form of Eris is Eridian. As a result, for a time the object known to the wider public as Xena. Xena was a name used internally by the discovery team. It was inspired by the character of the television series Xena. The discovery team had saved the nickname Xena for the first body they discovered that was larger than Pluto
23.
C/1861 G1
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Comet C/1861 G1 is a long-period comet with roughly a 415-year orbit discovered by A. E. Thatcher. It is responsible for the Lyrid meteor shower, carl Wilhelm Baeker also independently found this comet. The comet passed about 0.335 AU from the Earth on 1861-May-05, Thatcher at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
24.
Eridanus (constellation)
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Eridanus is a constellation in the southern hemisphere. It is represented as a river and it was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern constellations, the same name was later taken as a Latin name for the real Po River and also for the name of a minor river in Athens. At its southern end is the magnitude 0.5 star Achernar,144 light-years from Earth, it is a blue-white hued main sequence star whose traditional name means the rivers end. Achernar is a very peculiar star because it is one of the flattest stars known, observations indicate that its radius is about 50% larger at the equator than at the poles. This distortion occurs because the star is spinning extremely rapidly, there are several other noteworthy stars in Eridanus, including some double stars. Beta Eridani, traditionally called Cursa, is a star of magnitude 2.8,89 light-years from Earth. Its place to the south of Orions foot gives it its name, theta Eridani, called Acamar, is a binary star with blue-white components, distinguishable in small amateur telescopes and 161 light-years from Earth. The primary is of magnitude 3.2 and the secondary is of magnitude 4.3,32 Eridani is a binary star 290 light-years from Earth. The primary is a star of magnitude 4.8. 32 Eridani is divisible in amateur telescopes. 39 Eridani is a binary star divisible in small amateur telescopes,206 light-years from Earth. The primary is a giant star of magnitude 4.9. 40 Eridani is a star system consisting of an orange main-sequence star, a white dwarf. The orange main-sequence star is the primary of magnitude 4.4, the red dwarf, of magnitude 11, orbits the white dwarf every 250 years. The 40 Eridani system is 16 light-years from Earth, P Eridani is a binary star with two orange components,27 light-years from Earth. The magnitude 5.8 primary and 5.9 secondary have a period of 500 years. Epsilon Eridani is a star with one extrasolar planet similar to Jupiter and it is an orange-hued main-sequence star of magnitude 3.7,10.5 light-years from Earth
25.
Procyon
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Procyon, also designated Alpha Canis Minoris, is the brightest star in the constellation of Canis Minor. To the naked eye, it appears to be a single star and it is a binary star system, consisting of a white main-sequence star of spectral type F5 IV–V, named Procyon A, and a faint white dwarf companion of spectral type DQZ, named Procyon B. As determined by the European Space Agency Hipparcos astrometry satellite, it lies at a distance of just 11.46 light-years, and is therefore one of Earths nearest stellar neighbours. Its closest neighboring star is Luytens Star, about 1.12 ly away, Procyon is the eighth-brightest star in the night sky, culminating at midnight on January 14. It forms one of the three vertices of the Winter Triangle asterism, in combination with Sirius and Betelgeuse, the prime period for evening viewing of Procyon is in late winter. It has a index of 0.42, and its hue has been described as having a faint yellow tinge to it. Procyon is a star system with a bright primary component, Procyon A, having an apparent magnitude of 0.34. The pair orbit each other with a period of 40.82 years along an orbit with an eccentricity of 0.407. The plane of their orbit is inclined at an angle of 31. 1° to the line of sight with the Earth. The average separation of the two components is 15.0 AU, a less than the distance between Uranus and the Sun, though the eccentric orbit carries them as close as 8.9 AU. The primary has a classification of F5IV–V, indicating that it is a late-stage F-type main-sequence star. As it continues to expand, the star will eventually swell to about 80 to 150 times its current diameter and this will probably happen within 10 to 100 million years. The effective temperature of the atmosphere is an estimated 6,530 K. It is 1.5 times the mass, twice the solar radius. Both the core and the envelope of this star are convective, in late June 2004, Canadas orbital MOST satellite telescope carried out a 32-day survey of Procyon A. The continuous optical monitoring was intended to confirm solar-like oscillations in its brightness observed from Earth, no oscillations were detected and the authors concluded that the theory of stellar oscillations may need to be reconsidered. However, others argued that the non-detection was consistent with published ground-based radial velocity observations of solar-like oscillations, photometric measurements from the NASA Wide Field Infrared Explorer satellite from 1999 and 2000 showed evidence of granulation and solar-like oscillations. Unlike the MOST result, the variation seen in the WIRE photometry was in agreement with radial velocity measurements from the ground, like Sirius B, Procyons companion is a white dwarf that was inferred from astrometric data long before it was observed
26.
Sirius
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Sirius is a star system and the brightest star in the Earths night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the system has the Bayer designation Alpha Canis Majoris. The distance separating Sirius A from its companion varies between 8.2 and 31.5 AU, Sirius appears bright because of its intrinsic luminosity and its proximity to Earth. At a distance of 2.6 parsecs, as determined by the Hipparcos astrometry satellite, Sirius is gradually moving closer to the Solar System, so it will slightly increase in brightness over the next 60,000 years. After that time its distance will begin to increase and it will become fainter, Sirius A is about twice as massive as the Sun and has an absolute visual magnitude of 1.42. It is 25 times more luminous than the Sun but has a lower luminosity than other bright stars such as Canopus or Rigel. The system is between 200 and 300 million years old and it was originally composed of two bright bluish stars. Sirius is also known colloquially as the Dog Star, reflecting its prominence in its constellation, the brightest star in the night sky, Sirius is recorded in the earliest astronomical records. Every year, it disappears for seventy days before returning to the sky just before sunrise. This occurs at Cairo on 19 July, placing it just prior to the summer solstice, the ancient Greeks observed that the appearance of Sirius heralded the hot and dry summer and feared that it caused plants to wilt, men to weaken, and women to become aroused. Due to its brightness, Sirius would have been noted to twinkle more in the weather conditions of early summer. To Greek observers, this signified certain emanations which caused its malignant influence, anyone suffering its effects was said to be star-struck. It was described as burning or flaming in literature, the season following the stars reappearance came to be known as the dog days. The inhabitants of the island of Ceos in the Aegean Sea would offer sacrifices to Sirius and Zeus to bring cooling breezes, if it rose clear, it would portend good fortune, if it was misty or faint then it foretold pestilence. Coins retrieved from the island from the 3rd century BC feature dogs or stars with emanating rays, ptolemy of Alexandria mapped the stars in Books VII and VIII of his Almagest, in which he used Sirius as the location for the globes central meridian. He depicted it as one of six red-coloured stars, the other five are class M and K stars, such as Arcturus and Betelgeuse. Bright stars were important to the ancient Polynesians for navigation between the islands and atolls of the Pacific Ocean. Low on the horizon, they acted as stellar compasses and they also served as latitude markers, the declination of Sirius matches the latitude of the archipelago of Fiji at 17°S and thus passes directly over the islands each night
27.
Canopus
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Canopus, also designated Alpha Carinae, is the brightest star in the southern constellation of Carina, and the second brightest star in the night-time sky, after Sirius. Canopuss visual magnitude is −0.74, and it has a magnitude of −5.71. Canopus is a giant of spectral type A9, so it is essentially white when seen with the naked eye. It is located in the far southern sky, at a year 2000 declination of −52° 42′ and its name is generally considered to originate from the mythological Canopus, who was a navigator for Menelaus, king of Sparta. In Indian Vedic literature, the star Canopus is associated with the sage Agastya, Agastya, the star, is said to be the cleanser of waters and its rising coincides with the calming of the waters of the Indian Ocean. It is considered the son of Pulasthya, son of Brahma, Canopus was not visible to the mainland ancient Greeks and Romans, it was, however, visible to the ancient Egyptians. Hence Aratus did not write of the star as it remained below the horizon, while Eratosthenes and Ptolemy—observing from Alexandria—did, the Navajo named it Ma’ii Bizò‘. The Bedouin people of the Negev and Sinai also knew it as Suhayl, due to the fact that it disappears below the horizon in those regions, it became associated with a changeable nature, as opposed to always-visible Polaris, which was circumpolar and hence steadfast. It is also referred to by its Arabic name, سهيل, called the Old Man of the South Pole in Chinese, Canopus appears on the medieval Chinese manuscript the Dunhuang star chart, despite not being visible from the Chinese capital of Changan. The Chinese astronomer Yi Xing had journeyed south to chart Canopus, however, it was already mentioned by Sima Qian in the second century BC, drawing on sources from the Warring States period, as the southern counterpart of Sirius. Bright stars were important to the ancient Polynesians for navigation between the islands and atolls of the Pacific Ocean. Low on the horizon, they acted as stellar compasses to assist mariners in charting courses to particular destinations. The Hawaiian people called Canopus Ke Alii-o-kona-i-ka-lewa, The chief of the expanse, it was one of the stars used by Hawaii-loa. The Māori people of New Zealand/Aotearoa had several different names for Canopus, ariki, was known as a solitary star that appeared in the east, prompting people to weep and chant. They also named it Atutahi, Aotahi or Atuatahi, Stand Alone and its solitary nature indicates it is a tapu star, as tapu people are often solitary. Its appearance at the beginning of the Maruaroa season foretells the coming winter, light rays to the south indicate a cold wet winter, food was offered to the star on its appearance. This name has several different mythologies attached to it as well, one story tells of how Atutahi was left outside of the basket representing the Milky Way when Tāne wove it. Another related myth surrounding the star says that Atutahi was the child of Rangi
28.
Right ascension
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Right ascension is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question. When combined with declination, these astronomical coordinates specify the direction of a point on the sphere in the equatorial coordinate system. Right ascension is the equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a direction on an equator. Right ascension is measured continuously in a circle from that equinox towards the east. Any units of measure could have been chosen for right ascension, but it is customarily measured in hours, minutes. Astronomers have chosen this unit to measure right ascension because they measure a stars location by timing its passage through the highest point in the sky as the Earth rotates. The highest point in the sky, called meridian, is the projection of a line onto the celestial sphere. A full circle, measured in units, contains 24 × 60 × 60 = 86 400s, or 24 × 60 = 1 440m. Because right ascensions are measured in hours, they can be used to time the positions of objects in the sky. For example, if a star with RA = 01h 30m 00s is on the meridian, sidereal hour angle, used in celestial navigation, is similar to right ascension, but increases westward rather than eastward. Usually measured in degrees, it is the complement of right ascension with respect to 24h and it is important not to confuse sidereal hour angle with the astronomical concept of hour angle, which measures angular distance of an object westward from the local meridian. The Earths axis rotates slowly westward about the poles of the ecliptic and this effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates are inherently relative to the year of their observation, coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. The right ascension of Polaris is increasing quickly, the North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18h and 6h respectively. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC. But Hipparchus and his successors made their star catalogs in ecliptic coordinates, the easiest way to do that is to use an equatorial mount, which allows the telescope to be aligned with one of its two pivots parallel to the Earths axis
29.
Declination
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In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declinations angle is measured north or south of the celestial equator, the root of the word declination means a bending away or a bending down. It comes from the root as the words incline and recline. Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere, points north of the celestial equator have positive declinations, while those south have negative declinations. Any units of measure can be used for declination, but it is customarily measured in the degrees, minutes. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere, the Earths axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, therefore, equatorial coordinates are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch. Coordinates from different epochs must be rotated to match each other. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity. This similarly occurs in the Southern Hemisphere for objects with less than −90° − φ. An extreme example is the star which has a declination near to +90°. Circumpolar stars never dip below the horizon, conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earths surface. Generally, if a star whose declination is δ is circumpolar for some observer, then a star whose declination is −δ never rises above the horizon, as seen by the same observer. Likewise, if a star is circumpolar for an observer at latitude φ, neglecting atmospheric refraction, declination is always 0° at east and west points of the horizon. At the north point, it is 90° − |φ|, and at the south point, from the poles, declination is uniform around the entire horizon, approximately 0°. Non-circumpolar stars are visible only during certain days or seasons of the year, the Suns declination varies with the seasons. As seen from arctic or antarctic latitudes, the Sun is circumpolar near the summer solstice, leading to the phenomenon of it being above the horizon at midnight
30.
Granville Stuart
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Widely known as Mr. Montana, Granvilles life spanned the formative years of Montana from territorial times through the first 30 years of statehood. His journals and writings have provided Montana and western historians unique insights into life in the Northern Rockies during the half the 19th Century. Granville Stuart was born August 27,1834 in Harrison County, Virginia to parents Robert and he was their second son and brother to their first son, James Stuart. In 1838, the Stuarts after a stay in Illinois, moved to Muscatine County, Iowa near present-day West Liberty. It was in frontier Iowa that a young Granville and his brother James learned to hunt, explore, in 1849, Granvilles father Robert made his way to the California gold fields as a Forty-niner but had little luck. In 1851 he returned to the family in Iowa, in the Spring of 1852 Granville and his brother James accompanied their father west on the Oregon Trail back to California. By the summer of 1853 Robert was tired of gold prospecting, the brothers Granville and James stayed in the Sacramento, California area to make their own life. After failing to strike it rich in Sacramento, they moved to Yreka in June 1854 and their military career lasted about a month without any encounter with hostile Indians. They returned to Yreka to prospect but by the Spring of 1857 had decided to return overland to the family in Iowa, Granville and James, along with nine other travelers, were en route east when Granville fell seriously ill in southern Idaho. Granville was too ill to travel so James stayed with him while the others went east, by the time Granville recovered, it was too late in the year to continue east over the Rocky Mountains. The brothers could not winter over in southern Idaho nor could they seek refuge in Salt Lake City because of the conflict between the United States and the Mormons called the Mormon War. Instead they befriended a former fur trapper Jake Meek who wintered a small herd in the Beaverhead Valley. On October 10,1857, Granville and James Stuart and Jake Meek crossed Monida Pass 200 miles north into the Beaverhead Valley and they established a camp along the Beaverhead River near present-day Dillon, Montana. Others were already in the valley, many former fur traders had adopted the practice trading one good cow or oxen for two trail weary animals on the Oregon Trail during the summer. They overwintered the animals in the Beaverhead to get healthy for the next summer. One of these traders was French-Canadian Richard Grant, father of Johnny Grant who established the Grant Ranch in Deer Lodge in 1862. For three years, the Stuart brothers traded cattle, horses and other goods between the Big Hole valley, the Beaverhead-Deerlodge Valley and Fort Bridger in Southern Wyoming. In the Fall of 1860, along with their friend Reece Andersen and they established a camp on Gold Creek, where in 1852 a French prospector, Francois Finley had discovered gold
31.
Montana
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Montana /mɒnˈtænə/ is a state in the Western region of the United States. The states name is derived from the Spanish word montaña, Montana has several nicknames, although none official, including Big Sky Country and The Treasure State, and slogans that include Land of the Shining Mountains and more recently The Last Best Place. Montana has a 545-mile border with three Canadian provinces, British Columbia, Alberta, and Saskatchewan, the state to do so. It also borders North Dakota and South Dakota to the east, Wyoming to the south, Montana is ranked 4th in size, but 44th in population and 48th in population density of the 50 United States. The western third of Montana contains numerous mountain ranges, smaller island ranges are found throughout the state. In total,77 named ranges are part of the Rocky Mountains, the eastern half of Montana is characterized by western prairie terrain and badlands. The economy is based on agriculture, including ranching and cereal grain farming. Other significant economic activities include oil, gas, coal and hard rock mining, lumber, the health care, service, and government sectors also are significant to the states economy. Millions of tourists annually visit Glacier National Park, the Little Bighorn Battlefield National Monument, the name Montana comes from the Spanish word Montaña and the Latin word Montana, meaning mountain, or more broadly, mountainous country. Montaña del Norte was the name given by early Spanish explorers to the mountainous region of the west. The name was changed by Representatives Henry Wilson and Benjamin F. Harding, when Ashley presented a bill to establish a temporary government in 1864 for a new territory to be carved out of Idaho, he again chose Montana Territory. This time Rep. Samuel Cox, also of Ohio, objected to the name, Cox complained that the name was a misnomer given most of the territory was not mountainous and that a Native American name would be more appropriate than a Spanish one. Other names such as Shoshone were suggested, but it was decided that the Committee on Territories could name it whatever they wanted, with an area of 147,040 square miles, Montana is slightly larger than Japan. It is the fourth largest state in the United States after Alaska, Texas, and California, the largest landlocked U. S. state, and the worlds 56th largest national state/province subdivision. To the north, Montana shares a 545-mile border with three Canadian provinces, British Columbia, Alberta, and Saskatchewan, the state to do so. It borders North Dakota and South Dakota to the east, Wyoming to the south, the states topography is roughly defined by the Continental Divide, which splits much of the state into distinct eastern and western regions. Most of Montanas 100 or more named mountain ranges are in the western half. The Absaroka and Beartooth ranges in the states south-central part are part of the Central Rocky Mountains
32.
Gary W. Kronk
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Gary W. Kronk is an American amateur astronomer and writer. Kronk was born in Granite City, Illinois, United States and this interest was focused even more by Comet Kohoutek. Kronk first observed this comet on November 30,1973, when he was a senior in high school and this observation provided the encouragement to research and write a paper about this comet and other great comets of the past for school. The teacher liked the paper so much, she submitted it to the local paper and he has been observing, researching, and writing about comets ever since. Kronk received a bachelor of degree in journalism from Southern Illinois University Edwardsville in 1981. He was then just shy of spending seven years in college as he struggled to find a major, in the end, he had a minor in English and extended studies in mathematics, physics, and psychology. Kronk is known as a observer, researcher, and writer. His latest book project is Cometography, which is a series being published by Cambridge University Press. His knowledge of the history of comets has led to the linking of several comets to older apparitions, Kronks comet research is also strongly aligned to meteor shower research, because of the relationship between the two fields. Charles P. Olivier Award, American Meteor Society,1999, the asteroid 48300 Kronk was named in his honor. Comets, A Descriptive Catalog, Enslow Publishers, Inc, Meteor Showers, Enslow Publishers, Inc. http, //meteorshowersonline. com Gary W. Kronks Bio Page Gary W. Kronk in libraries
33.
Fort Jefferson (Florida)
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Fort Jefferson is a massive but unfinished coastal fortress. It is the largest brick structure in the Americas, and is composed of over 16 million bricks. Among United States forts, only Fort Monroe in Virginia and Fort Adams in Rhode Island are larger, the fort is located on Garden Key in the lower Florida Keys within the Dry Tortugas National Park, about 70 miles west of the island of Key West. The Dry Tortugas are part of Monroe County, Florida, United States, in late December 1824 and early January 1825, about five years after Spain sold Florida to the United States for $5 million, U. S. Navy Commodore David Porter inspected the Dry Tortugas islands. He was on the lookout for a site for a station that would help suppress piracy in the Caribbean. Unimpressed with what he saw, he notified the Secretary of the Navy that the Dry Tortugas were unfit for any kind of naval establishment. A small island called Bush Key, later called Garden Key, was selected as the site for the lighthouse, construction began in 1825 and was completed in 1826. The 65-foot lighthouse was constructed of brick with a whitewashed exterior, a small white cottage for the lighthouse keeper was constructed beside the lighthouse. In 1829, under recommendations from Commodore John Rodgers, the USS Florida stopped at the Dry Tortugas to evaluate the anchorage, contrary to Commodore Porters experience, Josiah Tattnall was delighted with what he found. The Dry Tortugas, he reported, consisted of 11 small keys and surrounding reefs and banks, there was an outer and an inner harbor. The former afforded a safe anchorage at all seasons, and was enough to let a large number of ships ride at anchor. Of more importance, the inner harbor combined a sufficient depth of water for ships-of-the-line, Tattnall noted that if a hostile power should occupy the Dry Tortugas, United States shipping in the Gulf would be in deadly peril, and nothing but absolute naval superiority could prevail. However, if occupied and fortified by the U. S. the Dry Tortugas would constitute the advance post for a defense of the Gulf Coast. John G. Barnard then made a reconnaissance in Nov.1844 and on 17 Sept.1845. Construction of Fort Jefferson was finally begun on Garden Key in Dec.1846, under the supervision of 2nd Lt. Horatio Wright, after plans drawn up by Lt. Montgomery C. Meigs were approved in Nov. Meigs plans were based on a design by Joseph Totten Chief of Engineers Totten eventually visited the fort in 1855, accompanying Louis Agassiz. The new fort would be built so that the existing Garden Key lighthouse, the original brick lighthouse tower was taken down in 1877. The design called for a two-tiered casemates in a six-sided outline, corner bastions, which are large projections designed to allow defensive fire along the faces of the walls they joined, contained gunrooms, gunpowder magazines and a granite Spiral staircase
34.
University Press of Florida
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The University Press of Florida is the scholarly publishing arm of the State University System of Florida, representing Floridas twelve state universities. It is located in Gainesville near the University of Florida, one of the major research institutions. It is overseen by the Florida Board of Governors and publishes works from and its predecessor was the University of Florida Press. UPF has published almost 2,500 volumes with a staff of 41, a member of the Association of American University Presses, UPF ranks in the top-third of member presses for sales and new title production. As UPFs predecessor, the University of Florida Press, began to build a publishing program, other public universities in Florida took notice. To avoid replication of efforts among the campuses, the Florida Board of Regents established a decentralized, featuring independent editorial and financial controls on each of the state systems nine campuses, this structure brought all of the states public universities into the publishing process. By the early 1990s a need became apparent for one central authority that could refocus and unify the consortium’s publishing program, throughout the changes in organization, the press has maintained its status as the premier publisher of scholarly and general interest books in the state of Florida. Others have been named to Amazon. com’s best-seller list and chosen for book clubs, in 2006, UPF was hailed as a publishing powerhouse by the Gainesville Sun. Current publications by UPF can be found on the UPF website, UPF also publishes Orange Grove Texts Plus which are Open Access textbooks, and are available in an Open Access repository powered by the SobekCM Open Source software. State University System of Florida Florida Board of Governors University Press of Florida
35.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
36.
Coma (cometary)
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The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes close to the Sun on its highly elliptical orbit, as the comet warms, parts of it sublimes. This gives a comet a fuzzy appearance when viewed in telescopes and distinguishes it from stars, the word coma comes from the Greek kome, which means hair and is the origin of the word comet itself. The coma is generally made of ice and comet dust, water dominates up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun. The parent molecule is destroyed primarily through photodissociation and to a smaller extent photoionization. The solar wind plays a role in the destruction of water compared to photochemistry. Larger dust particles are left along the orbital path while smaller particles are pushed away from the Sun into the comets tail by light pressure. Comas typically grow in size as comets approach the Sun, and they can be as large as the diameter of Jupiter, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 also had a coma roughly the diameter of the Sun, even though the coma can become quite large, its size can actually decrease about the time it crosses the orbit of Mars around 1.5 AU from the Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, Comets were found to emit X-rays in late-March 1996. This surprised researchers, because X-ray emission is associated with very high-temperature bodies. This ripping off leads to the emission of X-rays and far ultraviolet photons, with basic Earth-surface based telescope and some technique, the size of the Coma can be calculated. Called the drift method, one locks the telescope in position and that time multiplied by the cosine of comets declination, times.25 should equal the comas diameter in arcminutes. If the distance to the comet is known, then the apparent size of the coma can be determined. In 2015, it was noted that the ALICE instrument on the ESA Rosetta spacecraft to comet 67/P, detected hydrogen, oxygen, carbon and nitrogen in the Coma, which they also called the Comets atmosphere. Alice is a spectrograph, and it found that electrons created by UV light were colliding and breaking up molecules of water. OAO-2 discovered large halos of hydrogen gas around comets, space probe Giotto detected hydrogen ions at distance of 7.8 million km away from Halley when it did close flyby of the comet in 1986. A hydrogen gas halo was detected to be 15 times the diameter of Sun and this triggered NASA to point the Pioneer Venus mission at the Comet, and it was determined that the Comet emitting 12 tons of water per second. The hydrogen gas emission has not been detected from Earths surface because those wavelengths are blocked by the atmosphere, the process by which water is broken down into hydrogen and oxygen was studied by the ALICE instrument aboard the Rosetta spacecraft
37.
Antitail
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An antitail is a spike projecting from a comets coma which seems to go towards the Sun, and thus geometrically opposite to the other tails, the ion tail and the dust tail. However, this phenomenon is an illusion that is seen from the Earth. As Earth passes through the orbital plane, this disc is seen side on. The other side of the disc can sometimes be seen, though it tends to be lost in the dust tail, the antitail is therefore normally visible for a brief interval only when Earth passes through the comets orbital plane. Comet tail The coma and tail at the main Comet article, image of Comet Arend-Roland with prominent antitail Emily Lakdawalla. Spot a comet near Saturn tonight, online Encyclopedia of Science - Antitail
38.
Comet dust
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Comet dust refers to cosmic dust that originates from a comet. Comet dust can provide clues to comets origin, when the Earth passes through a comet dust trail, it can produce a meteor shower. Bulk properties of the comet dust such as density as well as the composition can distinguish between the models. For example, the ratios of comet and of interstellar dust are very similar. The 1) interstellar model says that ices formed on dust grains in the cloud that preceded the Sun. The mix of ice and dust then aggregated into a comet without appreciable chemical modification, J. Mayo Greenberg first proposed this idea in 1986. In the 2) Solar System model, the ices that formed in the interstellar cloud first vaporized as part of the disk of gas. The vaporized ices later resolidified and assembled into comets, so the comets in this model would have a different composition than those comets that were made directly from interstellar ice. The 3) primordial rubble pile model for comet formation says that comets agglomerate in the region where Jupiter was forming, the composition of the dust of comet Wild 2 is similar to the composition of dust found in the outer regions of the accretion disks around newly-forming stars. A comet and its dust allow investigation of the Solar System beyond the main planetary orbits, comets are distinguished by their orbits, long period comets have long elliptical orbits, randomly inclined to the plane of the Solar System, and with periods greater than 200 years. A comet will experience a range of conditions as it traverses its orbit. For long period comets, most of the time it will be so far from the Sun that it will be too cold for evaporation of ices to occur, near the Sun, the heating and evaporation rate will be so great, that no dust can be retained. Therefore, the thickness of dust layers covering the nuclei of a comet can indicate how closely, if a comet has an accumulation of thick dust layers, it may have frequent perihelion passages that dont approach the Sun too closely. The accumulation of dust layers over time would change the character of the short-period comet. A dust layer both inhibits the heating of the cometary ices by the Sun, and slows the loss of gases from the nucleus below
39.
Meteor shower
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A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of debris called meteoroids entering Earths atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate, intense or unusual meteor showers are known as meteor outbursts and meteor storms, which may produce greater than 1000 meteors an hour. The Meteor Data Centre lists about 600 suspected meteor showers of which about 100 are well established, the first great storm in modern times was the Leonids of November 1833. American Denison Olmsted explained the event most accurately, after spending the last weeks of 1833 collecting information he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, and January 1836. Work continued, however, coming to understand the nature of showers though the occurrences of storms perplexed researchers. In the 1890s, Irish astronomer George Johnstone Stoney and British astronomer Arthur Matthew Weld Downing, were the first to attempt to calculate the position of the dust at Earths orbit. They studied the dust ejected in 1866 by comet 55P/Tempel-Tuttle in advance of the anticipated Leonid shower return of 1898 and 1899, Meteor storms were anticipated, but the final calculations showed that most of the dust would be far inside of Earths orbit. The same results were independently arrived at by Adolf Berberich of the Königliches Astronomisches Rechen Institut in Berlin, although the absence of meteor storms that season confirmed the calculations, the advance of much better computing tools was needed to arrive at reliable predictions. In 1981 Donald K. Yeomans of the Jet Propulsion Laboratory reviewed the history of showers for the Leonids. A graph from it was adapted and re-published in Sky and Telescope and it showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. In 1985, E. D. Kondrateva and E. A. Reznikov of Kazan State University first correctly identified the years when dust was released which was responsible for several past Leonid meteor storms, in 1995, Peter Jenniskens predicted the 1995 Alpha Monocerotids outburst from dust trails. In anticipation of the 1999 Leonid storm, Robert H. McNaught, David Asher, in 2006 Jenniskens has published predictions for future dust trail encounters covering the next 50 years. Jérémie Vaubaillon continues to update predictions based on each year for the Institut de Mécanique Céleste et de Calcul des Éphémérides. Because meteor shower particles are all traveling in parallel paths, and at the same velocity and this radiant point is caused by the effect of perspective, similar to parallel railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks. Meteor showers are almost always named after the constellation from which the appear to originate. This fixed point slowly moves across the sky during the due to the Earth turning on its axis. The radiant also moves slightly from night to night against the stars due to the Earth moving in its orbit around the sun
40.
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
41.
Main-belt comet
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Main-belt comets are bodies orbiting within the asteroid belt that have shown comet-like activity during part of their orbit. The Jet Propulsion Laboratory defines a main-belt asteroid as an asteroid with an axis of more than 2 AU but less than 3.2 AU. The first main-belt comet discovered is 7968 Elst–Pizarro and it was discovered in 1979 and was found to have a tail by Eric Elst and Guido Pizarro in 1996 and given the cometary designation 133P/Elst-Pizarro. Although quite a few comets have semimajor axes well within Jupiters orbit, main-belt comets differ in having small eccentricities. The first three identified main-belt comets all orbit within the part of the asteroid belt. It is not known how an outer Solar System body like the other comets could have made its way into a low-eccentricity orbit typical of the asteroid belt, some main-belt comets display a cometary dust tail only for a part of their orbit near perihelion. Activity in 133P/Elst–Pizarro is recurrent, having been observed at each of the last three perihelia, the activity persists for a month or several out of each 5-6 year orbit, and is presumably due to ice being uncovered by minor impacts in the last 100 to 1000 years. These impacts are suspected to excavate these subsurface pockets of volatile material helping to expose them to solar radiation, observations of Scheila indicated that large amounts of dust were kicked up by the impact of another asteroid of approximately 35 meters in diameter. In October 2013, observations of P/2013 R3, taken with the 10.4 m Gran Telescopio Canarias on the island of La Palma showed that this comet was breaking apart. The brightest A fragment was also detected at the position in CCD images obtained at the 1.52 m telescope of the Sierra Nevada Observatory in Granada on October 12. NASA reported on a series of images taken by the Hubble Space Telescope between October 29,2013 and January 14,2014 that show the separation of the four main bodies. The Yarkovsky–OKeefe–Radzievskii–Paddack effect, caused by sunlight, increased the rate until the centrifugal force caused the rubble pile to separate. The term main-belt comet is a based on orbit and the presence of an extended morphology. It does not imply that these objects are comets or that the material surrounding their nuclei was ejected by the sublimation of volatiles, identified members of this morphology class include, Centaur Extinct comet Henry Hsiehs Main-Belt Comets page has extensive details on Main-belt comets David Jewitt. J. Licandro New images obtained with the GTC
