David Dunlap Observatory Catalogue
David Dunlap Observatory Catalogue, known as the DDO or A Catalogue of Dwarf Galaxies, is a catalogue of dwarf galaxies, published in 1959 by Sidney van den Bergh. DDO 3 is a dwarf spheroidal galaxy, located in the northern constellation of Cassiopeia, near the border of Andromeda, it is a small satellite galaxy of the famous Messier 31, the largest galaxy in the Local Group. DDO 8 is a dwarf irregular galaxy in the constellation Cetus, near the border of Pisces, it was discovered in 1906 by a German astronomer Max Wolf. It is a member of the Local Group as well. DDO 69 is an irregular galaxy, located in the constellation of Leo, it is a small satellite galaxy of the Milky Way. DDO 70 is an irregular galaxy, in the constellation of Sextans, it is located 4.44 million light years away from Earth. DDO 74 lies 820,000 light years away in the constellation Leo, it is one of the most distant satellite galaxy of our Milky Way. The dwarf spheroidal galaxy is located only 12 arcminutes from Regulus, the light from Regulus makes the visibility of DDO 74 becomes poor, so it is difficult to be observed.
DDO 75 is an irregular galaxy located in the constellation Sextans, same as its neighbour DDO 70. When it is observed from Earth, it appears as a square in shape. DDO 82 is a Magellanic spiral galaxy lies 13 million light years away in the constellation Ursa Major. DDO 93 is a dwarf spheroidal galaxy, located in the constellation of Leo, it was discovered in 1950 by Albert George Wilson. It is one of the satellite galaxies of the Milky Way. DDO 155 is a dwarf irregular galaxy located 7.9 million light years away from Earth in the constellation of Virgo. People give a nickname to this galaxy, called'Imprint of a Foot' because of its shape. DDO 169 is a dwarf irregular galaxy in the constellation Canes Venatici, it is one of the members of the M51 Group. DDO 190 is a dwarf irregular galaxy, located in the constellation of Boötes, it is a member of the M94 Group as well. DDO 199 is a dwarf spheroidal galaxy, located in the northern constellation of Ursa Minor, it was discovered in 1955 by an American astronomer Albert George Wilson.
It is a satellite of the Milky Way as well. DDO 210 is a dwarf irregular galaxy in the constellation of Aquarius, it lies 3.2 ± 0.2 million light years from our Milky Way. DDO 216 is a dwarf irregular galaxy located in the constellation Pegasus. Aquarius Boötes Canes Venatici Cassiopeia Cetus Leo Pegasus Sextans Ursa Major Ursa Minor Virgo
Intermediate spiral galaxy
An intermediate spiral galaxy is a galaxy, in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification system devised by Gerard de Vaucouleurs. Subtypes are labeled as SAB0, SABa, SABb, or SABc, following a sequence analogous to the Hubble sequence for barred and unbarred spirals; the subtype is based on the relative prominence of the central bulge and how wound the spiral arms are
A disc galaxy is a galaxy characterized by a disc, a flattened circular volume of stars. These galaxies may not include a central non-disc-like region. Junko Ueda observed that galaxy collisions result in disc galaxies, within 40 million light years from the Earth. While the galaxies are interacting, they change shape in cosmic time. Disc galaxy types include: spiral galaxies unbarred spiral galaxies barred spiral galaxies intermediate spiral galaxies lenticular galaxies Galaxies that are not disc types include: elliptical galaxies irregular galaxies
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