The Sagittarius Dwarf Spheroidal Galaxy, a loop-shaped galaxy of the Milky Way, is which type of the three main classes of galaxy originally described by Edwin Hubble in "The Realm of the Nebulae?"
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Sagittarius Dwarf Spheroidal Galaxy The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It consists of four globular clusters, the main cluster having been discovered in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit (i.e. an orbit passing over the Milky Way’s galactic poles) at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large Magellanic Cloud). In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past.
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Elliptical galaxy An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. Unlike flat spiral galaxies with organization and structure, they are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center. They are one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work "The Realm of the Nebulae", along with spiral and lenticular galaxies. Elliptical galaxies range in shape from nearly spherical to highly flat and in size from tens of millions to over one hundred trillion stars. Originally Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false. Stars found inside of elliptical galaxies are on average much older than stars found in spiral galaxies.
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Unbarred spiral galaxy An unbarred spiral galaxy is a type of spiral galaxy without a central bar, or one that is not a barred spiral galaxy. It is designated with an SA in the galaxy morphological classification scheme.
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Dwarf galaxy problem The dwarf galaxy problem, also known as the missing satellites problem, arises from numerical cosmological simulations that predict the evolution of the distribution of matter in the universe. Dark matter seems to cluster hierarchically and in ever increasing number counts for smaller-and-smaller-sized halos. However, although there seem to be enough observed normal-sized galaxies to account for this distribution, the number of dwarf galaxies is orders of magnitude lower than expected from simulation. For comparison, there were observed to be around 38 dwarf galaxies in the Local Group, and only around 11 orbiting the Milky Way, (for a detailed and more up to date list see List of Milky Way's satellite galaxies) yet one dark matter simulation predicted around 500 Milky Way dwarf satellites.
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NGC 1313 NGC 1313 (also known as the Topsy Turvy Galaxy) is a field galaxy and a barred spiral galaxy discovered by the Scottish astronomer James Dunlop on 27 September 1826. It has a diameter of about 50,000 light-years, or one-third the size of the Milky Way.
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Pisces Dwarf Pisces Dwarf is an irregular dwarf galaxy that is part of the Local Group. The galaxy, taking its name from the constellation Pisces where it appears, is suspected of being a satellite galaxy of the Triangulum Galaxy (M33). It displays a blueshift, as it is approaching the Milky Way at 287 km/s. It may be transition-type galaxy, somewhere between dwarf spheroidal and dwarf irregular. Alternatively, it may be a rare, but statistically acceptable, version of one of the two types.
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NGC 343 NGC 343 are a pair of interacting galaxies in the constellation Cetus. It was discovered in 1886 by Frank Muller. It was described by Dreyer as "extremely faint, very small, irregularly round, suddenly brighter middle and nucleus (perhaps a star?)."
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NGC 425 NGC 425 is a spiral galaxy in the constellation of Andromeda. It was discovered on October 29, 1866 by Truman Safford.
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Ring Nebula The Ring Nebula (also catalogued as Messier 57, "M57" or "NGC 6720") is a planetary nebula in the northern constellation of Lyra. Such objects are formed when a shell of ionized gas is expelled into the surrounding interstellar medium by a red giant star, which was passing through the last stage in its evolution before becoming a white dwarf.
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Rosette Nebula The Rosette Nebula (also known as Caldwell 49) is a large spherical H II region (circular in appearance) located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, the stars of the cluster having been formed from the nebula's matter.
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NGC 373 NGC 373 is an elliptical galaxy located in the constellation Pisces. It was discovered on December 12, 1876 by Dreyer. It was described by Dreyer as "very faint, very small."
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NGC 1 NGC 1 is an intermediate spiral galaxy of the morphological type Sbc, located 210 million light-years away in the constellation Pegasus. It was discovered on 30 September 1861 by Heinrich d'Arrest, who described it as "faint, small, round, between 11th and 14th magnitude stars" (to the north and south).
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List of ring galaxies This is a list of ring galaxies. A ring galaxy is a galaxy with a circle-like appearance. Hoag's Object, discovered by Art Hoag in 1950, is the prototypical example of a ring galaxy.
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NGC 379 NGC 364 is a lenticular galaxy in the constellation Pisces. It was discovered on September 12, 1784 by William Herschel. It was described by Dreyer as "pretty faint, small, round, brighter middle".
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NGC 6822 NGC 6822 (also known as Barnard's Galaxy, IC 4895, or Caldwell 57) is a barred irregular galaxy approximately 1.6 million light-years away in the constellation Sagittarius. Part of the Local Group of galaxies, it was discovered by E. E. Barnard in 1884 (hence its name), with a six-inch refractor telescope. It is one of the closer galaxies to the Milky Way. It is similar in structure and composition to the Small Magellanic Cloud. It is about 7,000 light-years in diameter.
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NGC 3227 NGC 3227 is an intermediate spiral galaxy that is interacting with the dwarf elliptical galaxy NGC 3226. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the "Atlas of Peculiar Galaxies". Both galaxies may be found in the constellation Leo.
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Andromeda X Andromeda X (And 10) is a dwarf spheroidal galaxy about 2.9 million light-years away from the Sun in the constellation Andromeda. Discovered in 2005, And X is a satellite galaxy of the Andromeda Galaxy (M31).
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NGC 47 NGC 47 (also known as NGC 58, MCG -1-1-55, IRAS00119-0726 and PGC 967) is a barred spiral galaxy in the constellation Cetus, discovered in 1886 by Ernst Wilhelm Leberecht Tempel. Its alternate name NGC 58 is due to the observation by Lewis Swift, who was unaware that Tempel had already discovered the celestial object earlier. It appears as a small, faint spiral nebula with a bright core and is slightly oval.
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NGC 4041 NGC 4041 is the "New General Catalogue" identifier for a spiral galaxy in the northern circumpolar constellation of Ursa Major. It is located an estimated 70 million light years from the Sun. The morphological classification of SA(rs)bc indicates this is a spiral galaxy the lacks a bar; the 'rs' means it has a weakly-formed ring structure, and the 'bc' indicates the spiral arms are moderately to loosely wound.
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Galactic plane The galactic plane is the plane in which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. Most often, in actual usage, the terms "galactic plane" and "galactic poles" are used to refer specifically to the plane and poles of the Milky Way, which is the galaxy in which Planet Earth is located.
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Superbubble A superbubble or supershell is a cavity which is hundreds of light years across, and is filled with 10 K gas blown into the interstellar medium by multiple supernovae and stellar winds. The winds of newly born stars strip superbubbles of any dust or gas. The Solar System lies near the center of an old superbubble, known as the Local Bubble, whose boundaries can be traced by a sudden rise in dust extinction of stars at distances greater than a few hundred light years.
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Planetary nebula A planetary nebula, often abbreviated as PN or plural PNe, is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from old red giant stars late in their lives. The word "nebula" is Latin for mist or cloud, and the term "planetary nebula" is a misnomer that originated in the 1780s with astronomer William Herschel because when viewed through his telescope, these objects resemble the rounded shapes of planets. Herschel's name for these objects was popularly adopted and has not been changed. They are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years.