SIMBAD is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de France. SIMBAD was created by merging the Catalog of Stellar Identifications and the Bibliographic Star Index as they existed at the Meudon Computer Centre until 1979, expanded by additional source data from other catalogues and the academic literature; the first on-line interactive version, known as Version 2, was made available in 1981. Version 3, developed in the C language and running on UNIX stations at the Strasbourg Observatory, was released in 1990. Fall of 2006 saw the release of Version 4 of the database, now stored in PostgreSQL, the supporting software, now written in Java; as of 10 February 2017, SIMBAD contains information for 9,099,070 objects under 24,529,080 different names, with 327,634 bibliographical references and 15,511,733 bibliographic citations. The minor planet 4692 SIMBAD was named in its honour. Planetary Data System – NASA's database of information on SSSB, maintained by JPL and Caltech.
NASA/IPAC Extragalactic Database – a database of information on objects outside the Milky Way maintained by JPL. NASA Exoplanet Archive – an online astronomical exoplanet catalog and data service Bibcode SIMBAD, Strasbourg SIMBAD, Harvard
Sloan Digital Sky Survey
The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P. Sloan Foundation. Data collection began in 2000; the main galaxy sample has a median redshift of z = 0.1. Data release 8, released in January 2011, includes all photometric observations taken with the SDSS imaging camera, covering 14,555 square degrees on the sky. Data release 9, released to the public on 31 July 2012, includes the first results from the Baryon Oscillation Spectroscopic Survey spectrograph, including over 800,000 new spectra. Over 500,000 of the new spectra are of objects in the Universe 7 billion years ago. Data release 10, released to the public on 31 July 2013, includes all data from previous releases, plus the first results from the APO Galactic Evolution Experiment spectrograph, including over 57,000 high-resolution infrared spectra of stars in the Milky Way.
DR10 includes over 670,000 new BOSS spectra of galaxies and quasars in the distant universe. The publicly available images from the survey were made between 1998 and 2009. SDSS uses a dedicated 2.5 m wide-angle optical telescope. The imaging camera was retired in late 2009, since the telescope has observed in spectroscopic mode. Images were taken using a photometric system of five filters; these images are processed to produce lists of objects observed and various parameters, such as whether they seem pointlike or extended and how the brightness on the CCDs relates to various kinds of astronomical magnitude. For imaging observations, the SDSS telescope used the drift scanning technique, which tracks the telescope along a great circle on the sky and continuously records small strips of the sky; the image of the stars in the focal plane drifts along the CCD chip, the charge is electronically shifted along the detectors at the same rate, instead of staying fixed as in tracked telescopes.. This method allows consistent astrometry over the widest possible field, minimises overheads from reading out the detectors.
The disadvantage is minor distortion effects. The telescope's imaging camera is made up of 30 CCD chips, each with a resolution of 2048×2048 pixels, totaling 120 megapixels; the chips are arranged in 5 rows of 6 chips. Each row has a different optical filter with average wavelengths of 355.1, 468.6, 616.5, 748.1 and 893.1 nm, with 95% completeness in typical seeing to magnitudes of 22.0, 22.2, 22.2, 21.3, 20.5, for u, g, r, i, z respectively. The filters are placed on the camera in the order r, i, u, z, g. To reduce noise, the camera is cooled to 190 kelvins by liquid nitrogen. Using these photometric data, stars and quasars are selected for spectroscopy; the spectrograph operates by feeding an individual optical fibre for each target through a hole drilled in an aluminum plate. Each hole is positioned for a selected target, so every field in which spectra are to be acquired requires a unique plate; the original spectrograph attached to the telescope was capable of recording 640 spectra while the updated spectrograph for SDSS III can record 1000 spectra at once.
Over the course of each night, between six and nine plates are used for recording spectra. In spectroscopic mode, the telescope tracks the sky in the standard way, keeping the objects focused on their corresponding fibre tips; every night the telescope produces about 200 GB of data. During its first phase of operations, 2000–2005, the SDSS imaged more than 8,000 square degrees of the sky in five optical bandpasses, it obtained spectra of galaxies and quasars selected from 5,700 square degrees of that imaging, it obtained repeated imaging of a 300 square degree stripe in the southern Galactic cap. In 2005 the survey entered a new phase, the SDSS-II, by extending the observations to explore the structure and stellar makeup of the Milky Way, the SEGUE and the Sloan Supernova Survey, which watches after supernova Ia events to measure the distances to far objects; the survey covers over 7,500 square degrees of the Northern Galactic Cap with data from nearly 2 million objects and spectra from over 800,000 galaxies and 100,000 quasars.
The information on the position and distance of the objects has allowed the large-scale structure of the Universe, with its voids and filaments, to be investigated for the first time. All of these data were obtained in SDSS-I, but a small part of the footprint was finished in SDSS-II; the Sloan Extension for Galactic Understanding and Exploration obtained spectra of 240,000 stars in order to create a detailed three-dimensional map of the Milky Way. SEGUE data provide evidence for the age and phase space distribution of stars within the various Galactic components, providing crucial clues for understanding the structure, formation a
Auriga is one of the 88 modern constellations. Located north of the celestial equator, its name is the Latin word for “the charioteer”, associating it with various mythological beings, including Erichthonius and Myrtilus. Auriga is most prominent during winter evenings in the northern Hemisphere, along with the five other constellations that have stars in the Winter Hexagon asterism; because of its northern declination, Auriga is only visible in its entirety as far as 34° south. A large constellation, with an area of 657 square degrees, it is half the size of the largest constellation, Hydra, its brightest star, Capella, is an unusual multiple star system among the brightest stars in the night sky. Beta Aurigae is an interesting variable star in the constellation; because of its position near the winter Milky Way, Auriga has many bright open clusters in its borders, including M36, M37, M38, popular targets for amateur astronomers. In addition, it has one prominent nebula, the Flaming Star Nebula, associated with the variable star AE Aurigae.
In Chinese mythology, Auriga's stars were incorporated into several constellations, including the celestial emperors' chariots, made up of the modern constellation's brightest stars. Auriga is home to the radiant for the Aurigids, Zeta Aurigids, Delta Aurigids, the hypothesized Iota Aurigids; the first record of Auriga's stars was in Mesopotamia as a constellation called GAM, representing a scimitar or crook. However, this may have represented just the modern constellation as a whole. GAM in the MUL. APIN; the crook of Auriga shepherd. It was formed from most of the stars of the modern constellation. Bedouin astronomers created constellations that were groups of animals, where each star represented one animal; the stars of Auriga comprised a herd of goats, an association present in Greek mythology. The association with goats carried into the Greek astronomical tradition, though it became associated with a charioteer along with the shepherd. In Greek mythology, Auriga is identified as the mythological Greek hero Erichthonius of Athens, the chthonic son of Hephaestus, raised by the goddess Athena.
Erichthonius was credited to be the inventor of the quadriga, the four-horse chariot, which he used in the battle against the usurper Amphictyon, the event that made Erichthonius the king of Athens. His chariot was created in the image of the Sun's chariot, the reason Zeus placed him in the heavens; the Athenian hero dedicated himself to Athena and, soon after, Zeus raised him into the night sky in honor of his ingenuity and heroic deeds. Auriga, however, is sometimes described as Myrtilus, Hermes's son and the charioteer of Oenomaus; the association of Auriga and Myrtilus is supported by depictions of the constellation, which show a chariot. Myrtilus's chariot was destroyed in a race intended for suitors to win the heart of Oenomaus's daughter Hippodamia. Myrtilus earned his position in the sky when Hippodamia's successful suitor, killed him, despite his complicity in helping Pelops win her hand. After his death, Myrtilus's father Hermes placed him in the sky, yet another mythological association of Auriga is Theseus's son Hippolytus.
He was ejected from Athens after he refused the romantic advances of his stepmother Phaedra, who committed suicide as a result. He was revived by Asclepius. Regardless of Auriga's specific representation, it is that the constellation was created by the ancient Greeks to commemorate the importance of the chariot in their society. An incidental appearance of Auriga in Greek mythology is as the limbs of Medea's brother. In the myth of Jason and the Argonauts, as they journeyed home, Medea killed her brother and dismembered him, flinging the parts of his body into the sea, represented by the Milky Way; each individual star represents a different limb. Capella is associated with the mythological she-goat Amalthea, it forms an asterism with the stars Epsilon Aurigae, Zeta Aurigae, Eta Aurigae, the latter two of which are known as the Haedi. Though most associated with Amalthea, Capella has sometimes been associated with Amalthea's owner, a nymph; the myth of the nymph says that the goat's hideous appearance, resembling a Gorgon, was responsible for the Titans' defeat, because Zeus skinned the goat and wore it as his aegis.
The asterism containing the three goats had been a separate constellation. Before that, Capella was sometimes seen as its own constellation—by Pliny the Elder and Manilius—called Capra, Caper, or Hircus, all of which relate to its status as the "goat star". Zeta Aurigae and Eta Aurigae were first called the "Kids" by Cleostratus, an ancient Greek astronomer. Traditionally, illustrations of Auriga represent it as its driver; the charioteer has two kids under his left arm. However, depictions of Auriga have been inconsistent over the years; the reins in his right hand have been drawn as a whip, though Capella is always over his left shoulder and the Kids under his left arm. The 1488 atlas Hyginus deviated from this typical depiction by showing a four-wheeled cart driven by Auriga
Lewis A. Swift
Lewis A. Swift was an American astronomer who discovered 13 comets and 1,248 uncatalogued nebulae. Only William Herschel discovered more nebulae visually. Swift discovered or co-discovered a number of comets, including periodic comets 11P/Tempel-Swift-LINEAR, 64P/Swift-Gehrels, 109P/Swift-Tuttle, he discovered comets C/1877 G2, C/1878 N1, C/1879 M1, C/1881 J1, C/1881 W1, C/1892 E1, D/1895 Q1, C/1896 G1 and C/1899 E1, co-discovered C/1883 D1. Note, comet 54P/de Vico-Swift-NEAT was discovered by his son Edward D. Swift rather than by him, he discovered his last comet at the age of 79. He was one of the few people to see Comet Halley at two of its appearances, 76 years apart. In 1878 he believed he had observed two Vulcan-type planets. Apart from comets, he discovered hundreds of nebulae, such as IC 289, galaxies, such as NGC 6, NGC 19 and NGC 27, he independently observed NGC 17, leading to its separate listing in the New General Catalogue as NGC 34. According to Swift, he first became interested in astronomy as young boy after observing the Great Comet of 1843 while on his way to school in Clarkson, New York.
His teacher dismissed his observation, but three days the'discovery' of the comet was announced. Swift conducted his early observations in Rochester, NY,'lain out in the snow' in an alley on Ambrose Street or on the roof of Duffy's Cider Mill, he gained a patron in the Rochester patent medicine businessman Hulbert Harrington Warner, who financed the building of an observatory for Swift. A fund of $13,000 was raised to purchase a 16-inch telescope for Swift. Warner went bankrupt in the Panic of 1893, which ended his financial support, Swift went to California to become director of Mount Lowe Observatory, taking the 16 inch telescope with him, he was married twice, first to Lucretia Hunt in 1850 and to Carrie D. Topping in 1864. Edward D. Swift was his son by the latter wife. Swift was awarded the degree of Ph. D. from the University of Rochester. Swift received more medals than any other astronomer of his time including three made of gold from the Austrian Academy of Sciences in Vienna, four made of bronze from the Astronomical Society of the Pacific, the Laplace Medal from the Société astronomique de France.
In 1897 he was the first person awarded the Jackson-Gwilt Medal of the Royal Astronomical Society. The asteroid 5035 Swift is named in his honour. Works by or about Lewis A. Swift at Internet Archive The Story of Lewis Swift Lewis Swift L. Swift @ Astrophysics Data System
A nebula is an interstellar cloud of dust, hydrogen and other ionized gases. The term was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way; the Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others. Most nebulae are of vast size. A nebula, visible to the human eye from Earth would appear larger, but no brighter, from close by; the Orion Nebula, the brightest nebula in the sky and occupying an area twice the diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers. Although denser than the space surrounding them, most nebulae are far less dense than any vacuum created on Earth – a nebular cloud the size of the Earth would have a total mass of only a few kilograms. Many nebulae are visible due to fluorescence caused by embedded hot stars, while others are so diffuse they can only be detected with long exposures and special filters.
Some nebulae are variably illuminated by T Tauri variable stars. Nebulae are star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions the formations of gas and other materials "clump" together to form denser regions, which attract further matter, will become dense enough to form stars; the remaining material is believed to form planets and other planetary system objects. Around 150 AD, Claudius Ptolemaeus recorded, in books VII–VIII of his Almagest, five stars that appeared nebulous, he noted a region of nebulosity between the constellations Ursa Major and Leo, not associated with any star. The first true nebula, as distinct from a star cluster, was mentioned by the Persian astronomer Abd al-Rahman al-Sufi, in his Book of Fixed Stars, he noted "a little cloud". He cataloged the Omicron Velorum star cluster as a "nebulous star" and other nebulous objects, such as Brocchi's Cluster; the supernova that created the Crab Nebula, the SN 1054, was observed by Arabic and Chinese astronomers in 1054.
In 1610, Nicolas-Claude Fabri de Peiresc discovered the Orion Nebula using a telescope. This nebula was observed by Johann Baptist Cysat in 1618. However, the first detailed study of the Orion Nebula was not performed until 1659, by Christiaan Huygens, who believed he was the first person to discover this nebulosity. In 1715, Edmund Halley published a list of six nebulae; this number increased during the century, with Jean-Philippe de Cheseaux compiling a list of 20 in 1746. From 1751 to 1753, Nicolas Louis de Lacaille cataloged 42 nebulae from the Cape of Good Hope, most of which were unknown. Charles Messier compiled a catalog of 103 "nebulae" by 1781; the number of nebulae was greatly increased by the efforts of William Herschel and his sister Caroline Herschel. Their Catalogue of One Thousand New Nebulae and Clusters of Stars was published in 1786. A second catalog of a thousand was published in 1789 and the third and final catalog of 510 appeared in 1802. During much of their work, William Herschel believed that these nebulae were unresolved clusters of stars.
In 1790, however, he discovered a star surrounded by nebulosity and concluded that this was a true nebulosity, rather than a more distant cluster. Beginning in 1864, William Huggins examined the spectra of about 70 nebulae, he found that a third of them had the emission spectrum of a gas. The rest thus were thought to consist of a mass of stars. A third category was added in 1912 when Vesto Slipher showed that the spectrum of the nebula that surrounded the star Merope matched the spectra of the Pleiades open cluster, thus the nebula radiates by reflected star light. About 1923, following the Great Debate, it had become clear that many "nebulae" were in fact galaxies far from our own. Slipher and Edwin Hubble continued to collect the spectra from many different nebulae, finding 29 that showed emission spectra and 33 that had the continuous spectra of star light. In 1932, Hubble announced that nearly all nebula are associated with stars, their illumination comes from star light, he discovered that the emission spectrum nebulae are nearly always associated with stars having spectral classifications of B or hotter, while nebulae with continuous spectra appear with cooler stars.
Both Hubble and Henry Norris Russell concluded that the nebulae surrounding the hotter stars are transfomed in some manner. There are a variety of formation mechanisms for the different types of nebulae; some nebulae form from gas, in the interstellar medium while others are produced by stars. Examples of the former case are giant molecular clouds, the coldest, densest phase of interstellar gas, which can form by the cooling and condensation of more diffuse gas. Examples of the latter case are planetary nebulae formed from material shed by a star in late stages of its stellar evolution. Star-forming regions are a class of emission nebula associated with giant molecular clouds; these form as a molecular cloud collapses under its own weight. Massive stars may form in the center, their ultraviolet radiation ionizes the surrounding gas, making it visible at optical wavelengths; the region of ionized hydrogen surrounding th
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas and dark matter. The word galaxy is derived from the Greek galaxias "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million stars to giants with one hundred trillion stars, each orbiting its galaxy's center of mass. Galaxies are categorized according to their visual morphology as spiral, or irregular. Many galaxies are thought to have supermassive black holes at their centers; the Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, observed as it existed just 400 million years after the Big Bang. Research released in 2016 revised the number of galaxies in the observable universe from a previous estimate of 200 billion to a suggested 2 trillion or more, containing more stars than all the grains of sand on planet Earth.
Most of the galaxies are 1,000 to 100,000 parsecs in diameter and separated by distances on the order of millions of parsecs. For comparison, the Milky Way has a diameter of at least 30,000 parsecs and is separated from the Andromeda Galaxy, its nearest large neighbor, by 780,000 parsecs; the space between galaxies is filled with a tenuous gas having an average density of less than one atom per cubic meter. The majority of galaxies are gravitationally organized into groups and superclusters; the Milky Way is part of the Local Group, dominated by it and the Andromeda Galaxy and is part of the Virgo Supercluster. At the largest scale, these associations are arranged into sheets and filaments surrounded by immense voids; the largest structure of galaxies yet recognised is a cluster of superclusters, named Laniakea, which contains the Virgo supercluster. The origin of the word galaxy derives from the Greek term for the Milky Way, galaxias, or kyklos galaktikos due to its appearance as a "milky" band of light in the sky.
In Greek mythology, Zeus places his son born by a mortal woman, the infant Heracles, on Hera's breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and realizes she is nursing an unknown baby: she pushes the baby away, some of her milk spills, it produces the faint band of light known as the Milky Way. In the astronomical literature, the capitalized word "Galaxy" is used to refer to our galaxy, the Milky Way, to distinguish it from the other galaxies in our universe; the English term Milky Way can be traced back to a story by Chaucer c. 1380: "See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt." Galaxies were discovered telescopically and were known as spiral nebulae. Most 18th to 19th Century astronomers considered them as either unresolved star clusters or anagalactic nebulae, were just thought as a part of the Milky Way, but their true composition and natures remained a mystery. Observations using larger telescopes of a few nearby bright galaxies, like the Andromeda Galaxy, began resolving them into huge conglomerations of stars, but based on the apparent faintness and sheer population of stars, the true distances of these objects placed them well beyond the Milky Way.
For this reason they were popularly called island universes, but this term fell into disuse, as the word universe implied the entirety of existence. Instead, they became known as galaxies. Tens of thousands of galaxies have been catalogued, but only a few have well-established names, such as the Andromeda Galaxy, the Magellanic Clouds, the Whirlpool Galaxy, the Sombrero Galaxy. Astronomers work with numbers from certain catalogues, such as the Messier catalogue, the NGC, the IC, the CGCG, the MCG and UGC. All of the well-known galaxies appear in one or more of these catalogues but each time under a different number. For example, Messier 109 is a spiral galaxy having the number 109 in the catalogue of Messier, having the designations NGC 3992, UGC 6937, CGCG 269-023, MCG +09-20-044, PGC 37617; the realization that we live in a galaxy, one among many galaxies, parallels major discoveries that were made about the Milky Way and other nebulae. The Greek philosopher Democritus proposed that the bright band on the night sky known as the Milky Way might consist of distant stars.
Aristotle, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars that were large and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the World, continuous with the heavenly motions." The Neoplatonist philosopher Olympiodorus the Younger was critical of this view, arguing that if the Milky Way is sublunary it should appear different at different times and places on Earth, that it should have parallax, which it does not. In his view, the Milky Way is celestial. According to Mohani Mohamed, the Arabian astronomer Alhazen made the first attempt at observing and measuring the Milky Way's parallax, he thus "determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere." The Persian astronomer al-Bīrūnī
Right ascension is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the point above the earth in question. When paired with declination, these astronomical coordinates specify the direction of a point on the celestial sphere in the equatorial coordinate system. An old term, right ascension refers to the ascension, or the point on the celestial equator that rises with any celestial object as seen from Earth's equator, where the celestial equator intersects the horizon at a right angle, it contrasts with oblique ascension, the point on the celestial equator that rises with any celestial object as seen from most latitudes on Earth, where the celestial equator intersects the horizon at an oblique angle. Right ascension is the celestial equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a primary direction on an equator. Right ascension is measured from the Sun at the March equinox i.e. the First Point of Aries, the place on the celestial sphere where the Sun crosses the celestial equator from south to north at the March equinox and is located in the constellation Pisces.
Right ascension is measured continuously in a full circle from that alignment of Earth and Sun in space, that equinox, the measurement increasing towards the east. As seen from Earth, objects noted to have 12h RA are longest visible at the March equinox. On those dates at midnight, such objects will reach their highest point. How high depends on their declination. Any units of angular measure could have been chosen for right ascension, but it is customarily measured in hours and seconds, with 24h being equivalent to a full circle. Astronomers have chosen this unit to measure right ascension because they measure a star's location by timing its passage through the highest point in the sky as the Earth rotates; the line which passes through the highest point in the sky, called the meridian, is the projection of a longitude line onto the celestial sphere. Since a complete circle contains 24h of right ascension or 360°, 1/24 of a circle is measured as 1h of right ascension, or 15°. A full circle, measured in right-ascension units, contains 24 × 60 × 60 = 86400s, or 24 × 60 = 1440m, or 24h.
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 = 1h 30m 00s is at its meridian a star with RA = 20h 00m 00s will be on the/at its meridian 18.5 sidereal hours later. Sidereal hour angle, used in celestial navigation, is similar to right ascension, but increases westward rather than eastward. Measured in degrees, it is the complement of right ascension with respect to 24h, 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 Earth's axis rotates westward about the poles of the ecliptic, completing one cycle in about 26,000 years; this movement, 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, astronomers specify them with reference to a particular year, known as an epoch.
Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. Right ascension for "fixed stars" near the ecliptic and equator increases by about 3.05 seconds per year on average, or 5.1 minutes per century, but for fixed stars further from the ecliptic the rate of change can be anything from negative infinity to positive infinity. 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 used standard epoch is J2000.0, January 1, 2000 at 12:00 TT. The prefix "J" indicates. Prior to J2000.0, astronomers used the successive Besselian epochs B1875.0, B1900.0, B1950.0. 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 use of RA was limited to special cases.
With the invention of the telescope, it became possible for astronomers to observe celestial objects in greater detail, provided that the telescope could be kept pointed at the object for a period of time. The easiest way to do, to use an equatorial mount, which allows the telescope to be aligned with one of its two pivots parallel to the Earth's axis. A motorized clock drive is used with an equatorial mount to cancel out the Earth's rotation; as the equatorial mount became adopted for observation, the equatorial coordinate system, which includes right ascension, was adopted at the same time for simplicity. Equatorial mounts could be pointed at objects with known right ascension and declination by the use of setting circles; the first star catalog to use right ascen