1.
Celestial cartography
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Measuring the position and light of charted objects requires a variety of instruments and techniques. Uranographers have historically produced planetary position tables, star tables and star maps for use by amateur and professional astronomers. More recently computerized star maps have been compiled, and automated positioning of telescopes is accomplished using databases of stars, the word uranography derived from the Greek ουρανογραφια through the Latin uranographia. In Renaissance times, Uranographia was used as the title of various celestial atlases. During the 19th century, uranography was defined as the description of the heavens, elijah H. Burritt re-defined it as the geography of the heavens. The German word for uranography is Uranographie, the French is uranographie, a determining fact source for drawing star charts is naturally a star table. C, AD150, Almagest – contains the last known star table from antiquity, C.964, Book of the Fixed Stars, Arabic version of the Almagest by al-Sufi. 1627, Rudolphine Tables – contains the first West Enlightenment star table,1690, Prodromus Astronomiae – by Johannes Hevelius for his Firmamentum Sobiescanum,1,564 stars. 1729, Britannic Catalogue – by John Flamsteed for his Atlas Coelestis,1903, Bonner Durchmusterung – by Friedrich Wilhelm Argelander and collaborators, circa 460,000 stars. 15th century BC – The ceiling of the tomb TT71 for the Egyptian architect and minister Senenmut, poeticon astronomicon, allegedly by Gaius Julius Hyginus 1092 – Xin Yi Xiang Fa Yao, by Su Song, a horological treatise which had the earliest existent star maps in printed form. True Visual Magnitude Photographic Star Atlas, pasachoff, Wil Tirion charts SkyGX – Christopher Watson The Great Atlas of the Sky – Piotr Brych. 100,000 Stars Cartes du Ciel Celestia 3D Galaxy Map CyberSky GoSkyWatch Planetarium Google Sky KStars Stellarium SKY-MAP. ORG SkyMap Online WorldWide Telescope XEphem, monthly star maps for every location on Earth Easy to use monthly star maps for northern and southern hemispheres. Helpful target lists for naked eye, binocular, or telescope viewing, collection of rare star atlases, charts, and maps available in full digital facsimile at Linda Hall Library. The Great Atlas of the Sky – worlds largest printed atlas of the sky, navigable online map of the stars, Stellarmap. com. The Digital Collections of the Linda Hall Library include, Astronomy, Star Atlases, Charts, and Maps, Astronomy, Selected Images, a collection of high-resolution star map images. History of Cosmology, Views of the Stars, high-resolution scans of prints relating to the study of the structure of the cosmos, EDSM, an external community supporting the recording of exploration data in Elite, Dangerous. GalNet, the community news source for Elite, Dangerous galactic activity, Community Goal, More Imperial Warships. Article citing the discovery of the lost Jaques station
2.
Lowell Observatory
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Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, in 2011, the Observatory was named one of The Worlds 100 Most Important Places by TIME. It was at the Lowell Observatory that the dwarf planet Pluto was discovered in 1930 by Clyde Tombaugh, the Observatorys original 61-centimeter Alvan Clark & Sons Telescope is still in use today for public education. It was founded by astronomer Percival Lowell of Bostons well-known Lowell family and is overseen by a sole trustee, the first trustee was Lowells third cousin Guy Lowell. Percivals nephew Roger Putnam served from 1927–1967, followed by Rogers son Michael, Michaels brother William Lowell Putnam III, the observatory operates several telescopes at three locations in the Flagstaff area. The telescope, built in 1896 for $20,000, was assembled in Boston by Alvan Clark & Sons, also located on the Mars Hill campus is the 33-centimeter Pluto Discovery Telescope, used by Clyde Tombaugh in 1930 to discover the dwarf planet Pluto. Lowell is a partner with the United States Naval Observatory and Naval Research Laboratory in the Navy Precision Optical Interferometer also located at that site, the Observatory also operates smaller research telescopes at its historic site on Mars Hill and in Australia and Chile. Past Anderson Mesa, on the peak of Happy Jack, Lowell Observatory has also built and is commissioning the 4. 28-meter Discovery Channel Telescope in partnership with Discovery Communications, Inc. Aside from the array of research and discoveries listed below. When Harold L. Johnson took over as the director in 1952, in 1953, the current 53 cm telescope was erected. Beginning in 1954, this telescope began monitoring the brightness of two planets, and comparing these measurements with a reference set of sunlike stars. Lowell Observatory is building a major new reflecting telescope in partnership with Discovery Communications, located near Happy Jack, the primary mirror of the Discovery Channel Telescope will be 4.28 m in diameter. It will be notable for its uncommon meniscus design for such a large mirror. This mirror was ground and polished into its parabolic shape at the Optical Fabrication, Lowell Observatorys astronomers conduct research on a wide range of solar system and astrophysical topics using ground-based, airborne, and space-based telescopes. In addition, the Observatory staff designs and builds custom instrumentation for use on Lowells telescopes, for example, Lowell staff built a sophisticated high-speed camera for use on the Stratospheric Observatory for Infrared Astronomy. SOFIA is a joint project of the United States and German space agencies, Lowell, Percival, Pickering, W. H. and the founding of the Lowell Observatory. National Historic Landmarks Program, Lowell Observatory+ Historic American Buildings Survey No, aZ-206, Lowell Observatory,1400 West Mars Hill Road, Flagstaff, Coconino County, AZ HABS No. AZ-206-A, Lowell Observatory, Slipher Building HABS No, aZ-206-B, Lowell Observatory, Clark Dome HABS No
3.
Cooke triplet
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The Cooke triplet is a photographic lens designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York. It was the first lens system that allowed elimination of most of the distortion or aberration at the outer edge of lenses. A Cooke triplet comprises a flint glass element in the centre with a crown glass element on each side. In this design, the sum of all the curvatures times indices of refraction can be zero, the curvature of field is determined by the sum of the dioptres, but the focal length is not. At the time, the Cooke triplet was an advancement in lens design. It was superseded by later designs in high-end cameras, but is widely used in inexpensive cameras, including variations using aspheric elements. The triplet soon became a standard in lens design still used with low-end cameras today, the main optical manufacturers often further developed the original Cooke triplet that were produced for many decades. Binoculars as well as refracting telescopes often use triplets, the same holds for many projection lenses, e. g. for 35 mm slide projectors
4.
Pluto
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Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered, Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its planethood was questioned following the discovery of objects of similar size in the Kuiper belt. In 2005, Eris, which is 27% more massive than Pluto, was discovered and this led the International Astronomical Union to define the term planet formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet, Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—about one-sixth the mass of the Moon and one-third its volume. It has an eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, light from the Sun takes about 5.5 hours to reach Pluto at its average distance. Pluto has five moons, Charon, Styx, Nix, Kerberos. Pluto and Charon are sometimes considered a system because the barycenter of their orbits does not lie within either body. The IAU has not formalized a definition for binary dwarf planets, on July 14,2015, the New Horizons spacecraft became the first spacecraft to fly by Pluto. During its brief flyby, New Horizons made detailed measurements and observations of Pluto, on October 25,2016, at 05,48 pm ET, the last bit of data was received from New Horizons from its close encounter with Pluto on July 14,2015. In the 1840s, Urbain Le Verrier used Newtonian mechanics to predict the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranuss orbit was being disturbed by another planet besides Neptune, by 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search until his death in 1916, unknown to Lowell, his surveys had captured two faint images of Pluto on March 19 and April 7,1915, but they were not recognized for what they were. There are fourteen other known prediscovery observations, with the oldest made by the Yerkes Observatory on August 20,1909. Percivals widow, Constance Lowell, entered into a legal battle with the Lowell Observatory over her late husbands legacy. Tombaughs task was to image the night sky in pairs of photographs, then examine each pair
5.
Astrophotography
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Astrophotography is a specialized type of photography for recording photos of astronomical objects and large areas of the night sky. The first photograph of an object was taken in 1840. This is done by long time exposure since both film and digital cameras can accumulate and sum light photons over long periods of time. Astrophotography is a subdiscipline in amateur astronomy usually seeking aesthetically pleasing images rather than scientific data. Amateurs use a range of special equipment and techniques. With a few exceptions, astronomical photography employs long exposures since both film and digital imaging devices can accumulate and light photons over long periods of time, the amount of light hitting the film or detector is also increased by increasing the diameter of the primary optics being used. Since the Earth is constantly rotating, telescopes and equipment are rotated in the direction to follow the apparent motion of the stars overhead. This is accomplished by using either equatorial or computer-controlled altazimuth telescope mounts to keep celestial objects centered while the earth rotates, all telescope mount systems suffer from induced tracking error due to imperfect motor drives and mechanical sag of the telescope. Tracking errors are corrected by keeping a selected aiming point, usually a bright guide star, sometimes the object to be imaged is moving, so the telescope has to be kept constantly centered on that object. Guiding was formerly done manually throughout the exposure with an observer standing at the telescope making corrections to keep a cross hair on the guide star, since the advent of computer-controlled systems this is accomplished by an automated systems in professional and even amateur equipment. These all require specialized equipment such as telescopes designed for imaging, for wide field of view. Astronomical CCD cameras may use cryogenic cooling to reduce thermal noise, specialized filters are also used to record images in specific wavelengths. The development of astrophotography as a tool was pioneered in the mid-19th century for the most part by experimenters and amateur astronomers. Because of the long exposures needed to capture relatively faint astronomical objects. Early photographic processes also had limitations, the daguerreotype process was far too slow to record anything but the brightest objects, and the wet plate collodion process limited exposures to the time the plate could stay wet. The first-known attempt at astronomical photography was by Louis Jacques Mandé Daguerre, inventor of the process which bears his name. Tracking errors in guiding the telescope during the long exposure meant the photograph came out as an indistinct fuzzy spot, the Sun may have been first photographed in an 1845 daguerreotype by the French physicists Léon Foucault and Hippolyte Fizeau. No photographic alteration was caused by the light of the corona condensed by a lens for two minutes, during totality, on a sheet of paper prepared with bromide of silver, the Suns solar corona was first successfully imaged during the Solar eclipse of July 28,1851
6.
Asteroid
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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers
7.
Meteoroid
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A meteoroid is a small rocky or metallic body in outer space. Meteoroids are significantly smaller than asteroids, and range in size from small grains to 1 meter-wide objects, objects smaller than this are classified as micrometeoroids or space dust. Most are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars and this phenomenon is called a meteor or shooting star. A series of many meteors appearing seconds or minutes apart and appearing to originate from the fixed point in the sky is called a meteor shower. If that object withstands ablation from its passage through the atmosphere as a meteor and impacts with the ground, an estimated 15,000 tonnes of meteoroids, micrometeoroids and different forms of space dust enter Earths atmosphere each year. In 1995, Beech and Steel, writing in the Quarterly Journal of the Royal Astronomical Society, according to Rubin and Grossman, the minimum size of an asteroid is given by what can be discovered from Earth-bound telescopes, so the distinction between meteoroid and asteroid is fuzzy. Some of the smallest asteroids discovered are 2008 TS26 with H =33.2 and 2011 CQ1 with H =32.1 both with a size of 1 meter. Objects smaller than meteoroids are classified as micrometeoroids and cosmic dust, the Minor Planet Center does not use the term meteoroid. Almost all meteoroids contain extraterrestrial nickel and iron and they have three main classifications, iron, stone, and stony-iron. Some stone meteoroids contain grain-like inclusions known as chondrules and are called chondrites, stoney meteoroids without these features are called achondrites, which are typically formed from extraterrestrial igneous activity, they contain little or no extraterrestrial iron. The composition of meteoroids can be inferred as they pass through Earths atmosphere from their trajectories and their effects on radio signals also give information, especially useful for daytime meteors, which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams associated with a parent comet. Debris from meteoroid streams may eventually be scattered into other orbits, the study of meteorites also gives insights into the composition of non-ephemeral meteoroids. Most meteoroids come from the belt, having been perturbed by the gravitational influences of planets. Some meteoroids are pieces of planets or moons, such as Mars or our moon, meteoroids travel around the Sun in a variety of orbits and at various velocities. The fastest ones move at about 42 kilometers per second through space in the vicinity of Earths orbit, Earth travels at about 29.6 kilometers per second. Thus, when meteoroids meet Earths atmosphere head-on, the speed may reach about 71 kilometers per second. Meteoroids moving through Earths orbital space average about 20 km/s, on January 17,2013 at 05,21 PST, a 1 meter-sized comet from the Oort cloud entered Earth atmosphere over a wide area in California and Nevada
8.
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
9.
Refracting telescope
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A refracting telescope is a type of optical telescope that uses a lens as its objective to form an image. The refracting telescope design was used in spy glasses and astronomical telescopes but is also used for long focus camera lenses. A refractors magnification is calculated by dividing the length of the objective lens by that of the eyepiece. Refractors were the earliest type of optical telescope, Galileo Galilei, happening to be in Venice in about the month of May 1609, heard of the invention and constructed a version of his own. Galileo then communicated the details of his invention to the public, all refracting telescopes use the same principles. The objective in a refracting telescope refracts or bends light and this refraction causes parallel light rays to converge at a focal point, while those not parallel converge upon a focal plane. The telescope converts a bundle of rays to make an angle α. The ratio β/α is called the angular magnification and it equals the ratio between the retinal image sizes obtained with and without the telescope. Refracting telescopes can come in different configurations to correct for image orientation. Because the image was formed by the bending of light, or refraction, the design Galileo Galilei used in 1609 is commonly called a Galilean telescope. It used a convergent objective lens and a divergent eyepiece lens, a Galilean telescope, because the design has no intermediary focus, results in a non-inverted and upright image. Galileo’s best telescope magnified objects about 30 times, because of flaws in its design, such as the shape of the lens and the narrow field of view, the images were blurry and distorted. Despite these flaws, the telescope was still enough for Galileo to explore the sky. The Galilean telescope could view the phases of Venus, and was able to see craters on the Moon, parallel rays of light from a distant object would be brought to a focus in the focal plane of the objective lens. The eyepiece lens intercepts these rays and renders them parallel once more, non-parallel rays of light from the object traveling at an angle α1 to the optical axis travel at a larger angle after they passed through the eyepiece. This leads to an increase in the apparent angular size and is responsible for the perceived magnification, the final image is a virtual image, located at infinity and is the same way up as the object. The Keplerian telescope, invented by Johannes Kepler in 1611, is an improvement on Galileos design and it uses a convex lens as the eyepiece instead of Galileos concave one. The advantage of this arrangement is that the rays of light emerging from the eyepiece are converging and this allows for a much wider field of view and greater eye relief, but the image for the viewer is inverted
10.
Reflecting telescope
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A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the telescope which. Although reflecting telescopes produce other types of aberrations, it is a design that allows for very large diameter objectives. Almost all of the telescopes used in astronomy research are reflectors. Reflecting telescopes come in many variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is referred to as a catoptric telescope. The idea that curved mirrors behave like lenses dates back at least to Alhazens 11th century treatise on optics, the potential advantages of using parabolic mirrors, primarily reduction of spherical aberration with no chromatic aberration, led to many proposed designs for reflecting telescopes. The most notable being James Gregory, who published a design for a ‘reflecting’ telescope in 1663. It would be ten years, before the experimental scientist Robert Hooke was able to build this type of telescope, Isaac Newton has been generally credited with building the first reflecting telescope in 1668. It used a spherically ground metal primary mirror and a diagonal mirror in an optical configuration that has come to be known as the Newtonian telescope. A curved primary mirror is the reflector telescopes basic optical element that creates an image at the focal plane, the distance from the mirror to the focal plane is called the focal length. The primary mirror in most modern telescopes is composed of a glass cylinder whose front surface has been ground to a spherical or parabolic shape. A thin layer of aluminum is deposited onto the mirror. Some telescopes use primary mirrors which are made differently, molten glass is rotated to make its surface paraboloidal, and is kept rotating while it cools and solidifies. The resulting mirror shape approximates a desired paraboloid shape that requires grinding and polishing to reach the exact figure needed. Reflecting telescopes, just like any other system, do not produce perfect images. The use of mirrors avoids chromatic aberration but they produce other types of aberrations, to avoid this problem most reflecting telescopes use parabolic shaped mirrors, a shape that can focus all the light to a common focus. Field curvature - The best image plane is in general curved and it is sometimes corrected by a field flattening lens
11.
Catadioptric system
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A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses and curved mirrors. Catadioptric combinations are used in focusing systems such as lights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes. Other optical systems use lenses and mirrors are also referred to as catadioptric such as surveillance catadioptric sensors. Catadioptric combinations have been used in many optical systems. In the 1820s, Augustin-Jean Fresnel developed several catadioptric lighthouse reflectors, léon Foucault developed a catadioptric microscope in 1859 to counteract aberrations of using a lens to image objects at high power. In 1876 a French engineer, A. Mangin, invented what has come to be called the Mangin mirror, the two surfaces of the reflector have different radii to correct the aberration of the spherical mirror. Light passes through the glass twice, making the system act like a triplet lens. Mangin mirrors were used in searchlights, where they produced a true parallel beam. Catadioptric telescopes are optical telescopes that combine specifically shaped mirrors and lenses to form an image and their designs can have simple all-spherical surfaces and can take advantage of a folded optical path that reduces the mass of the telescope, making them easier to manufacture. Catadioptric dialytes are the earliest type of catadioptric telescope and they consist of a single-element refractor objective combined with a silver-backed negative lens. The first of these was the Hamiltonian telescope patented by W. F. Hamilton in 1814, there are several telescope designs that take advantage of placing one or more full-diameter lenses in front of a spherical primary mirror. Some of these designs have been adapted to create compact, long-focal-length catadioptric cassegrains, the Schmidt corrector, the first full-diameter corrector plate, was used in Bernhard Schmidts 1931 Schmidt camera. The relatively thin and lightweight corrector allows Schmidt cameras to be constructed in diameters up to 1.3 m, the design has lent itself to many Schmidt variants. Popular sub-types Schmidt–Cassegrain telescopes are one of the most popular commercial designs on the amateur astronomical market, the design replaces the Schmidt Camera film holder with a Cassegrain secondary mirror, making a folded optical path with a long focal length and a narrow field of view. Wartime secrecy kept these inventors from knowing about each others designs, albert Bouwers built a prototype meniscus telescope in August 1940 and patented it in February 1941. It used a spherically concentric meniscus and was suitable as a monochromatic astronomical camera. In a later design he added a cemented doublet to correct chromatic aberration, Dmitri Maksutov built a prototype for a similar type of meniscus telescope, the Maksutov telescope, in October 1941 and patented it in November of that same year. His design corrected spherical and chromatic aberrations by placing a weak negative-shaped meniscus corrector closer to the primary mirror, popular sub-types Maksutov–Cassegrain telescopes are the most commonly seen design that uses a meniscus corrector, a variant of the Maksutov telescope
12.
Schmidt camera
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A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. The design was invented by Bernhard Schmidt in 1930, a recent example is the Kepler spacecraft exoplanet finder. Other related designs are the Wright Camera and Lurie–Houghton telescope, the Schmidt camera was invented by German-Estonian optician Bernhard Schmidt in 1930. Its optical components are an easy-to-make spherical primary mirror, and an aspherical correcting lens, known as a Schmidt corrector plate, the film or other detector is placed inside the camera, at the prime focus. The design is noted for allowing very fast focal ratios, while controlling coma, Schmidt cameras have very strongly curved focal planes, thus requiring that the film, plate, or other detector be correspondingly curved. A field flattener, in its simplest form a lens in front of the film plate or detector, is sometimes used. Since the corrector plate is at the center of curvature of the mirror in this design the tube length can be very long for a wide-field telescope. Because of its field of view, the Schmidt camera is typically used as a survey instrument. These include astronomical surveys, comet and asteroid searches, and nova patrols, in addition, Schmidt cameras and derivative designs are frequently used for tracking artificial earth satellites. The first relatively large Schmidt telescopes were built at Hamburg Observatory, between 1945 and 1980, about 8 more large Schmidt telescopes were built around the world. One particularly famous and productive Schmidt camera is the Oschin Schmidt Telescope at Palomar Observatory and this instrument was used in the National Geographic Society - Palomar Observatory Sky Survey, the POSS-II survey, the Palomar-Leiden Surveys, and other projects. The technical improvements developed during this survey encouraged the development of the Second Palomar Observatory Sky Survey, the telescope used in the Lowell Observatory Near-Earth-Object Search is also a Schmidt camera. The Schmidt telescope of the Karl Schwarzschild Observatory is the largest Schmidt camera of the world, a Schmidt telescope was at the heart of the Hipparcos satellite from the European Space Agency. This was used in the Hipparcos Survey which mapped the distances of more than a million stars with unprecedented accuracy - this included 99% of all stars up to magnitude 11. The spherical mirror used in this telescope was extremely accurate, if scaled up to the size of the Atlantic Ocean, the Kepler photometer, mounted on the Kepler probe, and orbiting since March 2009, is the largest Schmidt camera launched into space. Starting in the early 1970s, Celestron marketed an 8-inch Schmidt Camera, the camera was focused in the factory and was made of materials with low expansion coefficients so it would never need to be focused in the field. Early models required the photographer to cut and develop individual frames of 35 mm film as the holder could only hold one frame of film. About 300 Celestron Schmidt Cameras were produced, the Schmidt system was popular, used in reverse, for television projection systems
13.
F-number
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The f-number of an optical system such as a camera lens is the ratio of the systems focal length to the diameter of the entrance pupil. It is a number that is a quantitative measure of lens speed. It is also known as the ratio, f-ratio, f-stop. The f-number is commonly indicated using a hooked f with the format f/N, the f-number N or f# is given by, N = f D where f is the focal length, and D is the diameter of the entrance pupil. It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the pupil diameter in terms of f and N. Ignoring differences in light transmission efficiency, a lens with a greater f-number projects darker images, the brightness of the projected image relative to the brightness of the scene in the lenss field of view decreases with the square of the f-number. Doubling the f-number decreases the brightness by a factor of four. To maintain the same photographic exposure when doubling the f-number, the time would need to be four times as long. Most lenses have a diaphragm, which changes the size of the aperture stop. The entrance pupil diameter is not necessarily equal to the aperture stop diameter, a 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A200 mm focal length f/4 lens has a pupil diameter of 50 mm. The 200 mm lenss entrance pupil has four times the area of the 100 mm lenss entrance pupil, a T-stop is an f-number adjusted to account for light transmission efficiency. The word stop is sometimes confusing due to its multiple meanings, a stop can be a physical object, an opaque part of an optical system that blocks certain rays. In photography, stops are also a used to quantify ratios of light or exposure. The one-stop unit is known as the EV unit. On a camera, the setting is traditionally adjusted in discrete steps. Each stop is marked with its corresponding f-number, and represents a halving of the light intensity from the previous stop. This corresponds to a decrease of the pupil and aperture diameters by a factor of 1/2 or about 0.7071, each element in the sequence is one stop lower than the element to its left, and one stop higher than the element to its right
14.
Objective (optics)
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In optical engineering, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be a lens or mirror, or combinations of several optical elements. They are used in microscopes, telescopes, cameras, slide projectors, CD players, objectives are also called object lenses, object glasses, or objective glasses. The objective lens of a microscope is the one at the bottom near the sample, at its simplest, it is a very high-powered magnifying glass, with very short focal length. This is brought close to the specimen being examined so that the light from the specimen comes to a focus inside the microscope tube. The objective itself is usually a cylinder containing one or more lenses that are made of glass. Microscope objectives are characterized by two parameters, magnification and numerical aperture, the magnification typically ranges from 4× to 100×. Numerical aperture for microscope lenses typically ranges from 0.10 to 1.25, corresponding to focal lengths of about 40 mm to 2 mm, respectively. A typical microscope has three or four lenses with different magnifications, screwed into a circular nosepiece which may be rotated to select the required lens. These lenses are often color coded for easier use, the least powerful lens is called the scanning objective lens, and is typically a 4× objective. The second lens is referred to as the objective lens and is typically a 10× lens. The most powerful out of the three is referred to as the large objective lens and is typically 40–100×. Some microscopes use an oil-immersion or water-immersion lens, which can have greater than 100. These objectives are designed for use with refractive index matching oil or water. These lenses give greater resolution at high magnification, numerical apertures as high as 1.6 can be achieved with oil immersion. Camera lenses need to cover a large plane so are made up of a number of optical lens elements to correct optical aberrations. Image projectors use objective lenses that simply reverse the function of a lens, with lenses designed to cover a large image plane. In a telescope the objective is the lens at the front end of a refractor or the primary mirror of a reflecting or catadioptric telescope
15.
Charge-coupled device
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A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by shifting the signals between stages within the one at a time. CCDs move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins, in recent years CCD has become a major technology for digital imaging. In a CCD image sensor, pixels are represented by p-doped metal-oxide-semiconductors capacitors, the charge-coupled device was invented in 1969 at AT&T Bell Labs by Willard Boyle and George E. Smith. The lab was working on bubble memory when Boyle and Smith conceived of the design of what they termed, in their notebook. The device could be used as a shift register, the essence of the design was the ability to transfer charge along the surface of a semiconductor from one storage capacitor to the next. The concept was similar in principle to the device, which was developed at Philips Research Labs during the late 1960s. The first patent on the application of CCDs to imaging was assigned to Michael Tompsett, the initial paper describing the concept listed possible uses as a memory, a delay line, and an imaging device. The first experimental device demonstrating the principle was a row of closely spaced metal squares on a silicon surface electrically accessed by wire bonds. The first working CCD made with integrated circuit technology was a simple 8-bit shift register and this device had input and output circuits and was used to demonstrate its use as a shift register and as a crude eight pixel linear imaging device. Development of the device progressed at a rapid rate, by 1971, Bell researchers led by Michael Tompsett were able to capture images with simple linear devices. Several companies, including Fairchild Semiconductor, RCA and Texas Instruments, picked up on the invention, fairchilds effort, led by ex-Bell researcher Gil Amelio, was the first with commercial devices, and by 1974 had a linear 500-element device and a 2-D100 x 100 pixel device. Steven Sasson, an engineer working for Kodak, invented the first digital still camera using a Fairchild 100 x 100 CCD in 1975. The first KH-11 KENNAN reconnaissance satellite equipped with charge-coupled device array technology for imaging was launched in December 1976, under the leadership of Kazuo Iwama, Sony also started a large development effort on CCDs involving a significant investment. Eventually, Sony managed to mass-produce CCDs for their camcorders, before this happened, Iwama died in August 1982, subsequently, a CCD chip was placed on his tombstone to acknowledge his contribution. He was also awarded the 2012 IEEE Edison Medal For pioneering contributions to imaging devices including CCD Imagers, cameras, in a CCD for capturing images, there is a photoactive region, and a transmission region made out of a shift register. An image is projected through a lens onto the capacitor array, once the array has been exposed to the image, a control circuit causes each capacitor to transfer its contents to its neighbor. The last capacitor in the array dumps its charge into a charge amplifier, by repeating this process, the controlling circuit converts the entire contents of the array in the semiconductor to a sequence of voltages
16.
Cardinal point (optics)
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In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system. These are the points, the principal points, and the nodal points. The only ideal system that has achieved in practice is the plane mirror. Cardinal points provide a way to simplify a system with many components. The cardinal points lie on the axis of the optical system. Each point is defined by the effect the optical system has on rays that pass through that point, the paraxial approximation assumes that rays travel at shallow angles with respect to the optical axis, so that sin θ ≈ θ and cos θ ≈1. Aperture effects are ignored, rays that do not pass through the stop of the system are not considered in the discussion below. The front focal point of a system, by definition, has the property that any ray that passes through it will emerge from the system parallel to the optical axis. The rear focal point of the system has the reverse property, the front and rear focal planes are defined as the planes, perpendicular to the optic axis, which pass through the front and rear focal points. An object infinitely far from the optical system forms an image at the focal plane. For objects a finite distance away, the image is formed at a different location, but rays that leave the object parallel to one another cross at the rear focal plane. A diaphragm or stop at the focal plane can be used to filter rays by angle, since. No matter where on the object the ray comes from, the ray will pass through the aperture as long as the angle at which it is emitted from the object is small enough. Note that the aperture must be centered on the axis for this to work as indicated. Using a sufficiently small aperture in the plane will make the lens telecentric. Similarly, the range of angles on the output side of the lens can be filtered by putting an aperture at the front focal plane of the lens. This is important for DSLR cameras having CCD sensors, the pixels in these sensors are more sensitive to rays that hit them straight on than to those that strike at an angle. A lens that does not control the angle of incidence at the detector will produce pixel vignetting in the images and this means that the lens can be treated as if all of the refraction happened at the principal planes
17.
Minute and second of arc
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A minute of arc, arcminute, arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn, one minute of arc is 1/21600 of a turn, a second of arc, arcsecond, or arc second is 1/60 of an arcminute, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 of a radian. To express even smaller angles, standard SI prefixes can be employed, the number of square arcminutes in a complete sphere is 4 π2 =466560000 π ≈148510660 square arcminutes. The standard symbol for marking the arcminute is the prime, though a single quote is used where only ASCII characters are permitted. One arcminute is thus written 1′ and it is also abbreviated as arcmin or amin or, less commonly, the prime with a circumflex over it. The standard symbol for the arcsecond is the prime, though a double quote is commonly used where only ASCII characters are permitted. One arcsecond is thus written 1″ and it is also abbreviated as arcsec or asec. In celestial navigation, seconds of arc are used in calculations. This notation has been carried over into marine GPS receivers, which normally display latitude and longitude in the format by default. An arcsecond is approximately the angle subtended by a U. S. dime coin at a distance of 4 kilometres, a milliarcsecond is about the size of a dime atop the Eiffel Tower as seen from New York City. A microarcsecond is about the size of a period at the end of a sentence in the Apollo mission manuals left on the Moon as seen from Earth, since antiquity the arcminute and arcsecond have been used in astronomy. The principal exception is Right ascension in equatorial coordinates, which is measured in units of hours, minutes. These small angles may also be written in milliarcseconds, or thousandths of an arcsecond, the unit of distance, the parsec, named from the parallax of one arcsecond, was developed for such parallax measurements. It is the distance at which the radius of the Earths orbit would subtend an angle of one arcsecond. The ESA astrometric space probe Gaia is hoped to measure star positions to 20 microarcseconds when it begins producing catalog positions sometime after 2016, there are about 1.3 trillion µas in a turn. Currently the best catalog positions of stars actually measured are in terms of milliarcseconds, apart from the Sun, the star with the largest angular diameter from Earth is R Doradus, a red supergiant with a diameter of 0.05 arcsecond. The dwarf planet Pluto has proven difficult to resolve because its angular diameter is about 0.1 arcsecond, space telescopes are not affected by the Earths atmosphere but are diffraction limited. For example, the Hubble space telescope can reach a size of stars down to about 0. 1″
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Astrometry
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Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of the Solar System and our galaxy, the history of astrometry is linked to the history of star catalogues, which gave astronomers reference points for objects in the sky so they could track their movements. This can be dated back to Hipparchus, who around 190 BC used the catalogue of his predecessors Timocharis, in doing so, he also developed the brightness scale still in use today. Hipparchus compiled a catalogue with at least 850 stars and their positions, hipparchuss successor, Ptolemy, included a catalogue of 1,022 stars in his work the Almagest, giving their location, coordinates, and brightness. Ibn Yunus observed more than 10,000 entries for the Suns position for years using a large astrolabe with a diameter of nearly 1.4 metres. In the 15th century, the Timurid astronomer Ulugh Beg compiled the Zij-i-Sultani, like the earlier catalogs of Hipparchus and Ptolemy, Ulugh Begs catalogue is estimated to have been precise to within approximately 20 minutes of arc. In the 16th century, Tycho Brahe used improved instruments, including large mural instruments, to measure star positions more accurately than previously, Taqi al-Din measured the right ascension of the stars at the Istanbul observatory of Taqi al-Din using the observational clock he invented. When telescopes became commonplace, setting circles sped measurements James Bradley first tried to measure stellar parallaxes in 1729, the stellar movement proved too insignificant for his telescope, but he instead discovered the aberration of light and the nutation of the Earths axis. His cataloguing of 3222 stars was refined in 1807 by Friedrich Bessel and he made the first measurement of stellar parallax,0.3 arcsec for the binary star 61 Cygni. Being very difficult to measure, only about 60 stellar parallaxes had been obtained by the end of the 19th century, astrographs using astronomical photographic plates sped the process in the early 20th century. Automated plate-measuring machines and more sophisticated technology of the 1960s allowed more efficient compilation of star catalogues. In the 1980s, charge-coupled devices replaced photographic plates and reduced optical uncertainties to one milliarcsecond and this technology made astrometry less expensive, opening the field to an amateur audience. In 1989, the European Space Agencys Hipparcos satellite took astrometry into orbit, operated from 1989 to 1993, Hipparcos measured large and small angles on the sky with much greater precision than any previous optical telescopes. During its 4-year run, the positions, parallaxes, and proper motions of 118,218 stars were determined with a degree of accuracy. A new Tycho catalog drew together a database of 1,058,332 to within 20-30 mas, additional catalogues were compiled for the 23,882 double/multiple stars and 11,597 variable stars also analyzed during the Hipparcos mission. Today, the catalogue most often used is USNO-B1.0, during the past 50 years,7,435 Schmidt camera plates were used to complete several sky surveys that make the data in USNO-B1.0 accurate to within 0.2 arcsec. In observational astronomy, astrometric techniques help identify stellar objects by their unique motions and it is instrumental for keeping time, in that UTC is basically the atomic time synchronized to Earths rotation by means of exact observations. Astrometry is an important step in the distance ladder because it establishes parallax distance estimates for stars in the Milky Way
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Stellar classification
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In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with absorption lines, each line indicates an ion of a certain chemical element, with the line strength indicating the abundance of that ion. The relative abundance of the different ions varies with the temperature of the photosphere, the spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photospheres temperature and density. Most stars are classified under the Morgan–Keenan system using the letters O, B, A, F, G, K, and M. Each letter class is subdivided using a numeric digit with 0 being hottest and 9 being coolest. The sequence has been expanded with classes for other stars and star-like objects that do not fit in the system, such as class D for white dwarfs. In the MK system, a luminosity class is added to the class using Roman numerals. This is based on the width of absorption lines in the stars spectrum. The full spectral class for the Sun is then G2V, indicating a main-sequence star with a temperature around 5,800 K, the conventional color description takes into account only the peak of the stellar spectrum. This means that the assignment of colors of the spectrum can be misleading. There are no green, indigo, or violet stars, likewise, the brown dwarfs do not literally appear brown. The modern classification system is known as the Morgan–Keenan classification, each star is assigned a spectral class from the older Harvard spectral classification and a luminosity class using Roman numerals as explained below, forming the stars spectral type. The spectral classes O through M, as well as more specialized classes discussed later, are subdivided by Arabic numerals. For example, A0 denotes the hottest stars in the A class, fractional numbers are allowed, for example, the star Mu Normae is classified as O9.7. The Sun is classified as G2, the conventional color descriptions are traditional in astronomy, and represent colors relative to the mean color of an A-class star, which is considered to be white. The apparent color descriptions are what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. However, most stars in the sky, except the brightest ones, red supergiants are cooler and redder than dwarfs of the same spectral type, and stars with particular spectral features such as carbon stars may be far redder than any black body. O-, B-, and A-type stars are called early type
20.
Proper motion
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The components of proper motion in the equatorial coordinate system are measured in seconds of time for right ascension and seconds of arc in declination. Their combined value is computed as the proper motion, which is expressed in seconds of arc per year or per century. Knowledge of the motion, distance, and radial velocity allow approximate calculations of a stars true motion in space in respect to the Sun. Proper motion is not entirely proper, because it includes a component due to the motion of the Solar System itself, over the course of centuries, stars appear to maintain nearly fixed positions with respect to each other, so that they form the same constellations over historical time. Ursa Major or Crux, for example, looks nearly the same now as they did hundreds of years ago, however, precise long-term observations show that the constellations change shape, albeit very slowly, and that each star has an independent motion. This motion is caused by the movement of the relative to the Sun. The proper motion is a vector and is thus defined by two quantities, its position angle and its magnitude. The first quantity indicates the direction of the motion on the celestial sphere. Proper motion may alternatively be defined by the changes per year in the stars right ascension and declination. The components of motion by convention are arrived at as follows. Suppose in a year an object moves from coordinates to coordinates, then the changes of angle in seconds of arc per year are, The magnitude of the proper motion μ is given by vector addition of its components, where δ is the declination. The factor in cos δ accounts for the fact that the radius from the axis of the sphere to its surface varies as cos δ, becoming, for example, zero at the pole. Thus, the component of velocity parallel to the corresponding to a given angular change in α is smaller the further north the objects location. The change μα, which must be multiplied by cos δ to become a component of the motion, is sometimes called the proper motion in right ascension. Hence, the proper motions in right ascension and declination are made equivalent for straightforward calculations of various other stellar motions. Position angle θ is related to these components by, Motions in equatorial coordinates can be converted to motions in galactic coordinates, for the majority of stars seen in the sky, the observed proper motions are usually small and unremarkable. Such stars are either faint or are significantly distant, have changes of below 10 milliarcseconds per year. A few do have significant motions, and are usually called high-proper motion stars, Motions can also be in almost seemingly random directions
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Variable star
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A variable star is a star whose brightness as seen from Earth fluctuates. Many, possibly most, stars have at least some variation in luminosity, an ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol. This discovery, combined with supernovae observed in 1572 and 1604, proved that the sky was not eternally invariable as Aristotle. In this way, the discovery of variable stars contributed to the revolution of the sixteenth. The second variable star to be described was the eclipsing variable Algol, by Geminiano Montanari in 1669, chi Cygni was identified in 1686 by G. Kirch, then R Hydrae in 1704 by G. D. Maraldi. By 1786 ten variable stars were known, John Goodricke himself discovered Delta Cephei and Beta Lyrae. Since 1850 the number of variable stars has increased rapidly, especially after 1890 when it became possible to identify variable stars by means of photography. The latest edition of the General Catalogue of Variable Stars lists more than 46,000 variable stars in the Milky Way, as well as 10,000 in other galaxies, and over 10,000 suspected variables. The most common kinds of variability involve changes in brightness, but other types of variability also occur, by combining light curve data with observed spectral changes, astronomers are often able to explain why a particular star is variable. Variable stars are generally analysed using photometry, spectrophotometry and spectroscopy, measurements of their changes in brightness can be plotted to produce light curves. Peak brightnesses in the curve are known as maxima, while troughs are known as minima. By estimating the magnitude and noting the time of observation a visual lightcurve can be constructed. The American Association of Variable Star Observers collects such observations from participants around the world, from the light curve the following data are derived, are the brightness variations periodical, semiperiodical, irregular, or unique. What is the period of the brightness fluctuations, what is the shape of the light curve. From the spectrum the following data are derived, what kind of star is it, what is its temperature, is it a single star, or a binary. does the spectrum change with time. In very few cases it is possible to make pictures of a stellar disk and these may show darker spots on its surface. Combining light curves with spectral data often gives a clue as to the changes occur in a variable star. For example, evidence for a star is found in its shifting spectrum because its surface periodically moves toward and away from us
22.
Nova
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A nova or classical nova is an astronomical event that causes the sudden appearance of a bright new star, that slowly fades from view over several weeks or many months. Novae should not be confused with more energetic astronomical phenomena known as supernovae. Several main sub-classes of novae exist, based on their many different scenarios, being classical novae, recurrent novae, dwarf novae and they are together under a group of variable stars collectively known as cataclysmic variable stars, which share some common properties as close binary systems. Classical novae eruptions are the most common type of novae and they are likely created in a close binary star system consisting of a white dwarf and either a main sequence, sub-giant or red giant star. This mostly hydrogen atmosphere is heated from the hot white dwarf star, which eventually reaches a critical temperature. A few novae produce short-lived nova remnants, lasting several centuries. Recurrent nova processes are the same as the classical nova, except that the ignition can be repeated because the companion star can again feed the dense atmosphere of the white dwarf. Occurrences of novae mostly occur in the sky along the path of the Milky Way, however, it is also quite possible for them to appear anywhere in the sky. They are far more frequent than galactic supernovae, presently averaging about ten per year, the majority are found telescopically, with few reaching naked-eye visibility, perhaps averaging about once every year to eighteen months. Novae reaching 1st or 2nd magnitude occur only several times per century, the last bright nova was V1369 Centauri reaching 3.3 magnitude on 14 December 2013. During the 16th century, astronomer Tycho Brahe observed the supernova SN1572 in the constellation Cassiopeia and he described it in his book De nova stella, giving rise to the name nova. In this work he argued that an object should be seen to move relative to the fixed stars. Though this was a supernova and not a nova, the terms were considered interchangeable until the 1930s, after this, novae were classified as classical novae to distinguishing them from supernovae, as their causes and energies were though to be different based soley in the observational evidence. Evolution of potential novae begins with two main stars in a binary system. One of the two evolves into a red giant leaving its remnant white dwarf core in orbit with the remaining star, the second star—which may be either a main sequence star or an aging giant—begins to shed its envelope onto its white dwarf companion when it overflows its Roche lobe. As a result, the white dwarf captures matter in an accretion disk steadily from the outer atmosphere. As the white dwarf consists of matter, so the accreted hydrogen does not inflate. Rapid, an all at once, uncontrolled fusion occurs when the temperature of this layer reaches ~20 million Kelvins
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Planet
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The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye and these were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, in 2006, the International Astronomical Union officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of mass based on where or what they orbit. The planets were thought by Ptolemy to orbit Earth in deferent, at about the same time, by careful analysis of pre-telescopic observation data collected by Tycho Brahe, Johannes Kepler found the planets orbits were not circular but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the planets share characteristics such as volcanism, hurricanes, tectonics. Planets are generally divided into two types, large low-density giant planets, and smaller rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System, in order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites, several thousands of planets around other stars have been discovered in the Milky Way. e. in the habitable zone. On December 20,2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20. A2012 study, analyzing gravitational microlensing data, estimates an average of at least 1.6 bound planets for every star in the Milky Way, around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone. The idea of planets has evolved over its history, from the lights of antiquity to the earthly objects of the scientific age. The concept has expanded to include not only in the Solar System. The ambiguities inherent in defining planets have led to much scientific controversy, the five classical planets, being visible to the naked eye, have been known since ancient times and have had a significant impact on mythology, religious cosmology, and ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky, as opposed to the fixed stars, ancient Greeks called these lights πλάνητες ἀστέρες or simply πλανῆται, from which todays word planet was derived. In ancient Greece, China, Babylon, and indeed all pre-modern civilizations, it was almost universally believed that Earth was the center of the Universe and that all the planets circled Earth. The first civilization known to have a theory of the planets were the Babylonians
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Blink comparator
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A blink comparator was a viewing apparatus used by astronomers to find differences between two photographs of the night sky. It permitted rapidly switching from viewing one photograph to viewing the other, blinking back and this allowed the user to more easily spot objects in the night sky that changed position. It was also known as a blink microscope. It was invented by physicist Carl Pulfrich at Carl Zeiss AG, then constituted as Carl-Zeiss-Stiftung, photographs taken at longer intervals could be used to detect stars with large proper motion, or variable stars, or to distinguish binary stars from optical doubles. The most notable body to be using this technique was Pluto. The Projection Blink Comparator, invented by amateur astronomer Ben Mayer, was a low-cost version of the professional tool and it consisted of two slide projectors with a rotating occluding disk that alternatingly blocked the images from the projectors. This tool allowed amateur astronomers to contribute to some phases of serious research, in modern times, CCDs have largely replaced photographic plates and astronomical images are stored digitally on computer. The blinking technique can easily be performed on a screen rather than with a physical blink comparator apparatus as before. The blinking technique is used today because image differencing algorithms detect moving objects more effectively than human eyes can. This is particularly effective in cases where the object is very faint
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Clyde Tombaugh
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Clyde William Tombaugh was an American astronomer. He discovered Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper belt, at the time of discovery, Pluto was considered a planet but was later reclassified as a dwarf planet in 2006. He also called for the scientific research of unidentified flying objects. Tombaugh was born in Streator, Illinois, son of Muron Dealvo Tombaugh, a farmer, after his family moved to Burdett, Kansas in 1922, Tombaughs plans for attending college were frustrated when a hailstorm ruined his familys farm crops. Starting in 1926, he built several telescopes with lenses and mirrors by himself, to better test his telescope mirrors, Tombaugh, with just a pick and shovel, dug a pit 24 feet long,8 feet deep, and 7 feet wide. This provided a constant air temperature, free of air currents and he sent drawings of Jupiter and Mars to the Lowell Observatory, which offered him a job. Tombaugh worked there from 1929 to 1945, following his discovery of Pluto, Tombaugh earned bachelors and masters degrees in astronomy from the University of Kansas in 1936 and 1938. During World War II he taught naval personnel navigation at Northern Arizona University and he worked at White Sands Missile Range in the early 1950s, and taught astronomy at New Mexico State University from 1955 until his retirement in 1973. The asteroid 1604 Tombaugh, discovered in 1931, is named after him and he discovered hundreds of asteroids, beginning with 2839 Annette in 1929, mostly as a by-product of his search for Pluto and his searches for other celestial objects. Tombaugh named some of them after his wife, children and grandchildren, the Royal Astronomical Society awarded him the Jackson-Gwilt Medal in 1931. In 1980, he wrote a book Out of the Darkness, in August 1992, JPL scientist Robert Staehle called Tombaugh, requesting permission to visit his planet. I told him he was welcome to it, Tombaugh later remembered, though hes got to go one long, the call eventually led to the launch of the New Horizons space probe to Pluto in 2006. Following the passage on July 14,2015 of Pluto by the New Horizons spacecraft the Cold Heart of Pluto was named Tombaugh Regio, Tombaugh died on January 17,1997, when he was in Las Cruces, New Mexico, at the age of 90. A small portion of his ashes was placed aboard the New Horizons spacecraft, the container includes the inscription, Interred herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar systems third zone. Adelle and Murons boy, Patricias husband, Annette and Aldens father, astronomer, teacher, punster, Tombaugh was survived by his wife, Patricia, and their children, Annette and Alden. Tombaugh was an active Unitarian-Universalist, and he and his wife helped found the Unitarian Universalist Church of Las Cruces, through the daughter of his youngest brother, Robert M. Tombaugh is the great uncle of Los Angeles Dodgers pitcher Clayton Kershaw. Tombaugh used the observatorys 13-inch astrograph to take photographs of the section of sky several nights apart. He then used a blink comparator to compare the different images, when he shifted between the two images, a moving object, such as a planet, would appear to jump from one position to another, while the more distant objects such as stars would appear stationary
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Dwarf planet
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A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. The International Astronomical Union currently recognizes five dwarf planets, Ceres, Pluto, Haumea, Makemake, another hundred or so known objects in the Solar System are suspected to be dwarf planets. Individual astronomers recognize several of these, and in August 2011 Mike Brown published a list of 390 candidate objects, Stern states that there are more than a dozen known dwarf planets. Only two of these bodies, Ceres and Pluto, have observed in enough detail to demonstrate that they actually fit the IAUs definition. The IAU accepted Eris as a dwarf planet because it is more massive than Pluto and they subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 are to be named under the assumption that they are dwarf planets. The classification of bodies in other systems with the characteristics of dwarf planets has not been addressed. Starting in 1801, astronomers discovered Ceres and other bodies between Mars and Jupiter which were for some decades considered to be planets. Between then and around 1851, when the number of planets had reached 23, astronomers started using the asteroid for the smaller bodies. With the discovery of Pluto in 1930, most astronomers considered the Solar System to have nine planets and it was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet. Although it was more than ten times as massive as the largest object in the asteroid belt, Ceres. In the 1990s, astronomers began to find objects in the region of space as Pluto. Many of these shared several of Plutos key orbital characteristics, and Pluto started being seen as the largest member of a new class of objects and this led some astronomers to stop referring to Pluto as a planet. Several terms, including subplanet and planetoid, started to be used for the now known as dwarf planets. By 2005, three trans-Neptunian objects comparable in size to Pluto had been reported and it became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified. Astronomers were also confident that more objects as large as Pluto would be discovered, Eris was discovered in January 2005, it was thought to be slightly larger than Pluto, and some reports informally referred to it as the tenth planet. As a consequence, the became a matter of intense debate during the IAU General Assembly in August 2006. The IAUs initial draft proposal included Charon, Eris, and Ceres in the list of planets, dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, because they have not cleared their orbits. The IAUs final Resolution 5A preserved this three-category system for the bodies orbiting the Sun
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Ecliptic
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The ecliptic is the apparent path of the Sun on the celestial sphere, and is the basis for the ecliptic coordinate system. It also refers to the plane of this path, which is coplanar with the orbit of Earth around the Sun, the motions as described above are simplifications. Due to the movement of Earth around the Earth–Moon center of mass, due to further perturbations by the other planets of the Solar System, the Earth–Moon barycenter wobbles slightly around a mean position in a complex fashion. The ecliptic is actually the apparent path of the Sun throughout the course of a year, because Earth takes one year to orbit the Sun, the apparent position of the Sun also takes the same length of time to make a complete circuit of the ecliptic. With slightly more than 365 days in one year, the Sun moves a little less than 1° eastward every day, again, this is a simplification, based on a hypothetical Earth that orbits at uniform speed around the Sun. The actual speed with which Earth orbits the Sun varies slightly during the year, for example, the Sun is north of the celestial equator for about 185 days of each year, and south of it for about 180 days. The variation of orbital speed accounts for part of the equation of time, if the equator is projected outward to the celestial sphere, forming the celestial equator, it crosses the ecliptic at two points known as the equinoxes. The Sun, in its apparent motion along the ecliptic, crosses the equator at these points, one from south to north. The crossing from south to north is known as the equinox, also known as the first point of Aries. The crossing from north to south is the equinox or descending node. Likewise, the ecliptic itself is not fixed, the gravitational perturbations of the other bodies of the Solar System cause a much smaller motion of the plane of Earths orbit, and hence of the ecliptic, known as planetary precession. The combined action of two motions is called general precession, and changes the position of the equinoxes by about 50 arc seconds per year. Once again, this is a simplification, periodic motions of the Moon and apparent periodic motions of the Sun cause short-term small-amplitude periodic oscillations of Earths axis, and hence the celestial equator, known as nutation. Obliquity of the ecliptic is the used by astronomers for the inclination of Earths equator with respect to the ecliptic. It is about 23. 4° and is currently decreasing 0.013 degrees per hundred years due to planetary perturbations, the angular value of the obliquity is found by observation of the motions of Earth and other planets over many years. From 1984, the Jet Propulsion Laboratorys DE series of computer-generated ephemerides took over as the ephemeris of the Astronomical Almanac. Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated, jPLs fundamental ephemerides have been continually updated. J. Laskar computed an expression to order T10 good to 0″. 04/1000 years over 10,000 years, all of these expressions are for the mean obliquity, that is, without the nutation of the equator included
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Amateur astronomy
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Amateur astronomy is a hobby whose participants enjoy watching the sky, and the abundance of objects found in it with the unaided eye, binoculars, or telescopes. Many amateurs are beginners or hobbyists, while others have a degree of experience in astronomy and often assist. Amateur astronomers often look at the sky using nothing more than their eyes, people have studied the sky throughout history in an amateur framework, without any formal method of funding. It is only within about the past century, however, that amateur astronomy has become an activity clearly distinguished from professional astronomy, collectively, amateur astronomers observe a variety of celestial objects and phenomena. Common targets of amateur astronomers include the Moon, planets, stars, comets, meteor showers, and a variety of deep sky objects such as clusters, galaxies. Many amateurs like to specialise in observing particular objects, types of objects, one branch of amateur astronomy, amateur astrophotography, involves the taking of photos of the night sky. Most amateur astronomers work at visible wavelengths, but a small minority experiment with wavelengths outside the visible spectrum, non-visual amateur astronomy includes the use of infrared filters on conventional telescopes, and also the use of radio telescopes. Some amateur astronomers use home-made radio telescopes, while others use radio telescopes that were built for astronomy research but have since been made available for use by amateurs. The One-Mile Telescope is one such example, Amateur astronomers use a range of instruments to study the sky, depending on a combination of their interests and resources. Commercial telescopes are available, new and used, but it is common for amateur astronomers to build their own custom telescopes. Some people even focus on amateur telescope making as their primary interest within the hobby of amateur astronomy, although specialized and experienced amateur astronomers tend to acquire more specialized and more powerful equipment over time, relatively simple equipment is often preferred for certain tasks. Amateur astronomers also use star charts that, depending on experience and intentions, Amateur astronomers often like to keep records of their observations, which usually takes the form of an observing log. Observing logs typically record details about which objects were observed and when, sketching is sometimes used within logs, and photographic records of observations have also been used in recent times. The information gathered is used to help studies and interactions between amateur astronomers in yearly gatherings, although not professional information or credible, it is a way for the hobby lovers to share their new sightings and experiences. The Internet is a tool of amateur astronomers. The popularity of CCD imaging among amateurs has led to large numbers of web sites being written by individuals about their images, much of the social interaction of amateur astronomy occurs on mailing lists or discussion groups. Discussion group servers host numerous astronomy lists, a great deal of the commerce of amateur astronomy, the buying and selling of equipment, occurs online. Many amateurs use online tools to plan their observing sessions using tools such as the Clear Sky Chart
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Amateur telescope making
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Amateur telescope making is the activity of building telescopes as a hobby, as opposed to being a paid professional. Amateur telescope makers are usually a sub-group in the field of amateur astronomy, ever since Galileo took a Dutch invention and adapted it to astronomical use, astronomical telescope making has been an evolving discipline. Before the advent of modern mass-produced telescopes the price of even a modest instrument was often beyond the means of an amateur astronomer. Building your own was the only method to obtain a suitable telescope for observing. There were many published works that helped spark an interest in building such as Irish telescope maker Rev. W. F. A. Ellisons 1920 book The Amateurs Telescope. There was so much public interest Ingalls began a column for Scientific American on the subject. These had a readership of enthusiast constructing their own instruments. Between 1933 and 1990, Sky and Telescope magazine ran a column called Gleanings for ATMs edited by Earle Brown. The ready supply of surplus optical components after World War 2 and later Sputnik, porter as “The Poor Mans Telescope”. The Newtonian has the advantage of being a design that allows for maximum size for the minimum expense. Typically a Newtonian telescope of 6” or 8 aperture is a starter project. Since the Newtonian reflector is the most common telescope built by amateur telescope makers, the mirror has to be carefully ground, polished and figured to an extremely accurate shape, usually a paraboloid. Telescopes with high focal ratios may use spherical mirrors since the difference in the two shapes is insignificant at those ratios. The tools used to achieve this shape are surprisingly simple, consisting of a similarly sized glass tool, a series of finer abrasives, through a whole series of random strokes the mirror naturally tends to become spherical in shape. At that point, a variation in polishing strokes is used to create. In order to grind telescope optics into a shape, a highly versatile material must be used such as glass. After the melting point is reached, the glass fuses together, proper annealing procedures ensure that internal stresses are relieved within the glass, which reduces risk of failure for the newly cast blank. The equipment most amateurs use to test the shape of the mirrors, at its most basic it consists of a light bulb, a piece of tinfoil with a pinhole in it, and a razorblade
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Apochromat
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An apochromat, or apochromatic lens, is a photographic or other lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses. Chromatic aberration is the phenomenon of different colors focusing at different distances from a lens, in photography, chromatic aberration produces soft overall images, and color fringing at high-contrast edges, like an edge between black and white. Astronomers face similar problems, particularly with telescopes that use lenses rather than mirrors, achromatic lenses are corrected to bring two wavelengths into focus in the same plane. Apochromatic lenses are designed to bring three wavelengths into focus in the same plane, the residual color error can be up to an order of magnitude less than for an achromatic lens of equivalent aperture and focal length. Apochromats are also corrected for aberration at two wavelengths, rather than one as in an achromat. Apochromatic lenses for astrophotography in the 60–150 mm aperture range have been developed and marketed by different firms. Focused and guided properly during the exposure, these objectives are capable of producing the sharpest wide-field astrophotographs optically possible for the given aperture sizes. Graphic arts process cameras generally use apochromatic lenses for sharpest possible imagery as well, classically designed apochromatic process camera lenses generally have a maximum aperture limited to about f/9. More recently, higher-speed apo lenses have been produced for medium format, apochromatic designs require optical glasses with special dispersive properties to achieve three color crossings. In some cases, apochromatic designs without anomalous dispersion glasses are possible, also, when considering lens design, the APO designation is used more conservatively in astronomy-related optics than in photography. Achromat Superachromat Fluorite lens List of telescope types
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Newtonian telescope
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The Newtonian telescope is a type of reflecting telescope invented by the British scientist Sir Isaac Newton, using a concave primary mirror and a flat diagonal secondary mirror. Newton’s first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope, the Newtonian telescopes simple design makes it very popular with amateur telescope makers. Newtons idea for a telescope was not new. Newton may even have read James Gregorys 1663 book Optica Promota which described reflecting telescope designs using parabolic mirrors, Newton built his reflecting telescope because he suspected it could prove his theory that white light is composed of a spectrum of colours. Colour distortion was the fault of refracting telescopes of Newtons day. If this were true, then chromatic aberration could be eliminated by building a telescope which did not use a lens – a reflecting telescope, in late 1668 Isaac Newton built his first reflecting telescope. He chose an alloy of tin and copper as the most suitable material for his objective mirror and he later devised means for shaping and grinding the mirror and may have been the first to use a pitch lap to polish the optical surface. He chose a shape for his mirror instead of a parabola to simplify construction, even though it would introduce spherical aberration. This unique addition allowed the image to be viewed with minimal obstruction of the objective mirror and he also made the tube, mount, and fittings. Newtons first version had a mirror diameter of 1.3 inches. He found that the telescope worked without colour distortion and that he could see the four Galilean moons of Jupiter, Newtons friend Isaac Barrow showed a second telescope to a small group from the Royal Society of London at the end of 1671. They were so impressed with it that they demonstrated it to Charles II in January 1672, Newton was admitted as a fellow of the society in the same year. Like Gregory before him, Newton found it hard to construct an effective reflector and it was difficult to grind the speculum metal to a regular curvature. The surface also tarnished rapidly, the consequent low reflectivity of the mirror, because of these difficulties in construction, the Newtonian reflecting telescope was initially not widely adopted. In 1721 John Hadley showed a model to the Royal Society. Hadley had solved many of the problems of making a parabolic mirror and his Newtonian with a mirror diameter of 6 inches compared favourably with the large aerial refracting telescopes of the day. The size of reflecting telescopes subsequently grew rapidly, with designs doubling in primary mirror diameter about every 50 years and they are free of chromatic aberration found in refracting telescopes. Newtonian telescopes are usually less expensive for any given objective diameter than comparable quality telescopes of other types, since there is only one surface that needs to be ground and polished into a complex shape, overall fabrication is much simpler than other telescope designs
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Coma (optics)
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Specifically, coma is defined as a variation in magnification over the entrance pupil. In refractive or diffractive optical systems, especially those imaging a wide range, coma can be a function of wavelength. Coma is an inherent property of telescopes using parabolic mirrors, unlike a spherical mirror, a bundle of parallel rays parallel to the optical axis will be perfectly focused to a point, no matter where they strike the mirror. However, this is true if the rays are parallel to the axis of the parabola. When the incoming rays strike the mirror at an angle, individual rays are not reflected to the same point, when looking at a point that is not perfectly aligned with the optical axis, some of the incoming light from that point will strike the mirror at an angle. This results in an image that is not in the center of the field looking wedge-shaped, the further off-axis, the worse this effect is. This causes stars to appear to have a coma, hence the name. Schemes to reduce spherical aberration without introducing coma include Schmidt, Maksutov, ACF, correction lenses, coma correctors for Newtonian reflectors have been designed which reduce coma in telescopes below f/6. These work by means of a lens system of a plano-convex. Coma of a lens or a system of lenses can be minimized by choosing the curvature of the lens surfaces to match the application. Lenses in which both spherical aberration and coma are minimized at a wavelength are called bestform or aplanatic lenses. Vertical coma is the most common higher-order aberration in the eyes of patients with keratoconus, Coma is also a common temporary symptom of corneal injuries or abrasions, in which case the visual defect gradually resolves as the cornea heals. Aberration in optical systems Zernike polynomials About coma in a Newtonian telescope Coma Aberration in Youtube
