Principal Galaxies Catalogue
The Catalogue of Principal Galaxies is an astronomical catalog published in 1989 that lists B1950 and J2000 equatorial coordinates and cross-identifications for 73,197 galaxies. It is based on the Lyon-Meudon Extragalactic Database, started in 1983. 40,932 coordinates have standard deviations smaller than 10″. A total of 131,601 names from the 38 most common sources are listed. Available mean data for each object are given: 49,102 morphological descriptions, 52,954 apparent major and minor axis, 67,116 apparent magnitudes, 20,046 radial velocities and 24,361 position angles; the Lyon-Meudon Extragalactic Database was expanded into HyperLEDA, a database of a few million galaxies. Galaxies in the original PGC catalogue are numbered with their original PGC number in HyperLEDA. Numbers have been assigned for the other galaxies, although for those galaxies not in the original PGC catalogue, it is not recommended to use that number as a name. PGC 6240 is a large lenticular galaxy in the constellation Hydrus.
It is located about 106 million parsecs away from Earth. PGC 39058 is a dwarf galaxy, located 14 million light years away in the constellation of Draco, it is nearby, however it is obscured by a bright star, in front of the galaxy. Category:Principal Galaxies Catalogue objects Astronomical catalogue PGC info at ESO's archive of astronomical catalogues PGC readme at Centre de Données astronomiques de Strasbourg
NGC 5 is an elliptical galaxy in the constellation Andromeda. It has a generic "redshift estimated" distance of 212 million light years from Earth; the galaxy was discovered by French astronomer Edouard Stephan using an 80.01 cm reflecting telescope at the Marseille Observatory on 21 October 1881. The galaxy's position on the sky is RA 00h 07m 49s, Dec +35° 21' 44.3", just 0.2 arcmin west of the nucleus of NGC 4. As a magnitude 14 galaxy, its nucleus is small and faint, equivalent to a 13th or 14th magnitude star. NGC 5 has an estimated distance of 212 million light years from Earth, it is about 80 thousand light years across. NGC 5 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
Galaxy morphological classification
Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence, devised by Edwin Hubble and expanded by Gérard de Vaucouleurs and Allan Sandage; the Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. It is known colloquially as the “Hubble tuning-fork” because of the shape in which it is traditionally represented. Hubble's scheme divides galaxies into three broad classes based on their visual appearance: Elliptical galaxies have smooth, featureless light distributions and appear as ellipses in images, they are denoted by the letter "E", followed by an integer n representing their degree of ellipticity on the sky. Spiral galaxies consist of a flattened disk, with stars forming a spiral structure, a central concentration of stars known as the bulge, similar in appearance to an elliptical galaxy.
They are given the symbol "S". Half of all spirals are observed to have a bar-like structure, extending from the central bulge; these barred spirals are given the symbol "SB". Lenticular galaxies consist of a bright central bulge surrounded by an extended, disk-like structure but, unlike spiral galaxies, the disks of lenticular galaxies have no visible spiral structure and are not forming stars in any significant quantity; these broad classes can be extended to enable finer distinctions of appearance and to encompass other types of galaxies, such as irregular galaxies, which have no obvious regular structure. The Hubble sequence is represented in the form of a two-pronged fork, with the ellipticals on the left and the barred and unbarred spirals forming the two parallel prongs of the fork. Lenticular galaxies are placed between the ellipticals and the spirals, at the point where the two prongs meet the “handle”. To this day, the Hubble sequence is the most used system for classifying galaxies, both in professional astronomical research and in amateur astronomy.
The de Vaucouleurs system for classifying galaxies is a used extension to the Hubble sequence, first described by Gérard de Vaucouleurs in 1959. De Vaucouleurs argued that Hubble's two-dimensional classification of spiral galaxies—based on the tightness of the spiral arms and the presence or absence of a bar—did not adequately describe the full range of observed galaxy morphologies. In particular, he argued that rings and lenses are important structural components of spiral galaxies; the de Vaucouleurs system retains Hubble's basic division of galaxies into ellipticals, lenticulars and irregulars. To complement Hubble's scheme, de Vaucouleurs introduced a more elaborate classification system for spiral galaxies, based on three morphological characteristics: The different elements of the classification scheme are combined — in the order in which they are listed — to give the complete classification of a galaxy. For example, a weakly barred spiral galaxy with loosely wound arms and a ring is denoted SABc.
Visually, the de Vaucouleurs system can be represented as a three-dimensional version of Hubble's tuning fork, with stage on the x-axis, family on the y-axis, variety on the z-axis. De Vaucouleurs assigned numerical values to each class of galaxy in his scheme. Values of the numerical Hubble stage T run from −6 to +10, with negative numbers corresponding to early-type galaxies and positive numbers to late types. Elliptical galaxies are divided into three'stages': compact ellipticals, normal ellipticals and late types. Lenticulars are subdivided into early and late types. Irregular galaxies can be of type magellanic irregulars or'compact'; the use of numerical stages allows for more quantitative studies of galaxy morphology. Created by American astronomer William Wilson Morgan. Together with Philip Keenan, Morgan developed the MK system for the classification of stars through their spectra; the Yerkes scheme uses the spectra of stars in the galaxy. Thus, for example, the Andromeda Galaxy is classified as kS5.
Morphological Catalogue of Galaxies Galaxy color–magnitude diagram Galaxy Zoo William Wilson Morgan Fritz Zwicky Galaxies and the Universe - an introduction to galaxy classification Near-Infrared Galaxy Morphology Atlas, T. H. Jarrett The Spitzer Infrared Nearby Galaxies Survey Hubble Tuning-Fork, SINGS Spitzer Space Telescope Legacy Science Project Go to GalaxyZoo.org to try your hand at classifying galaxies as part of an Oxford University open community project
NGC 24 is a spiral galaxy in the Sculptor constellation. It was discovered by British astronomer William Herschel in 1785, measures some 40,000 light-years across. NGC 24 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
NGC 40 is a planetary nebula discovered by William Herschel on November 25, 1788, is composed of hot gas around a dying star. The star has ejected its outer layer which has left behind a smaller, hot star with a temperature on the surface of about 50,000 degrees Celsius. Radiation from the star causes the shed outer layer to heat to about 10,000 degrees Celsius, is about one light-year across. About 30,000 years from now, scientists theorize that NGC 40 will fade away, leaving only a white dwarf star the size of Earth. NGC 40 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
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
NGC 21 is a spiral galaxy in the Andromeda constellation. It was discovered by William Herschel in 1790. Lewis Swift observed it again in 1885. Wikisky image of NGC 29