A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.
Timeline of astronomical maps, catalogs and surveys
Nemesis is a hypothetical red dwarf or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU, somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years. In a 2017 paper, Sarah Sadavoy and Steven Stahler argued that the Sun was probably part of a binary system at the time of its formation, leading them to suggest "there probably was a Nemesis, a long time ago". Such a star would have separated from this binary system over four billion years ago, meaning it could not be responsible for the more recent perceived cycle of mass extinctions.
NGC 1 is an intermediate spiral galaxy of the morphological type Sbc, located in the constellation of Pegasus. It was discovered on 30 September 1861 by Heinrich d'Arrest.
The Canis Major Overdensity or Canis Major Dwarf Galaxy is a disputed dwarf irregular galaxy in the Local Group, located in the same part of the sky as the constellation Canis Major.
The NASA/IPAC Extragalactic Database (NED) is an online astronomical database for astronomers that collates and cross-correlates astronomical information on extragalactic objects. NED was created in the late 1980s by two Pasadena astronomers, George Helou and Barry F. Madore. NED is funded by NASA and is operated by the Infrared Processing and Analysis Center (IPAC) on the campus of the California Institute of Technology, under contract with NASA.
SIMBAD is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de Strasbourg (CDS), France.
NGC 520 is a pair of colliding spiral galaxies about 105 million light-years away in the constellation Pisces. They were discovered by astronomer William Herschel on 13 December 1784.
The Infrared Processing and Analysis Center (IPAC) provides science operations, data management, data archives and community support for astronomy and planetary science missions. IPAC has a historical emphasis on infrared-submillimeter astronomy and exoplanet science. IPAC has supported NASA, NSF and privately funded projects and missions. It is located on the campus of the California Institute of Technology in Pasadena, California.
Wide-field Infrared Survey Explorer is a NASA infrared astronomy space telescope in the Explorers Program launched in December 2009. WISE discovered thousands of minor planets and numerous star clusters. Its observations also supported the discovery of the first Y-type brown dwarf and Earth trojan asteroid. WISE performed an all-sky astronomical survey with images in 3.4, 4.6, 12 and 22 μm wavelength range bands, over ten months using a 40 cm (16 in) diameter infrared telescope in Earth orbit.
J. Davy Kirkpatrick is an American astronomer at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, California. Kirkpatrick's research was named one of the top ten science accomplishments of the first ten years (1992–2002) of the W. M. Keck Observatory and one of the Top 100 Stories of 2011 by Discover Magazine.
Disk Detective is the first NASA-led and funded-collaboration project with Zooniverse. It is NASA's largest crowdsourcing citizen science project aiming at engaging the general public in search of stars, which are surrounded by dust-rich circumstellar disks, where planets usually dwell and are formed. Initially launched by NASA Citizen Science Officer, Marc Kuchner, the principal investigation of the project was turned over to Steven Silverberg.
NGC 918 is a barred spiral galaxy in the constellation Aries, about 67 million light years from the Milky Way. It was discovered by John Herschel on Jan 11, 1831.
NGC 560 is a lenticular galaxy in the constellation Cetus. It is estimated to be about 250 million light-years from the Milky Way and has a diameter of approximately 150,000 light years. It is part of the Abell 194 galaxy cluster. NGC 560 was discovered on October 1, 1785 by the German-British astronomer William Herschel.
NGC 736 is an elliptical galaxy in the constellation Triangulum. It is an estimated 200 million light years from the Milky Way and has a diameter of approximately 85,000 light years. NGC 736 was discovered on September 12, 1784 by the German-British astronomer William Herschel.
NeVe 1 is a supergiant elliptical galaxy, which is the central, dominant member and brightest cluster galaxy (BCG) of the Ophiuchus Cluster. It lies at a distance of about 411 million light-years away from Earth and is located behind the Zone of Avoidance region in the sky. It is the host galaxy of the Ophiuchus Supercluster eruption, the most energetic astronomical event known.
NGC 551 is a spiral galaxy in the constellation Andromeda. It is estimated to be about 205 million light-years from the Milky Way. The object was discovered on 21, September 1786 by the German-British astronomer William Herschel.
NGC 855 is a star-forming dwarf elliptical galaxy located in the Triangulum constellation. The discovery and a first description was realized by William Herschel on 26th October 1786 and the findings made public through his Catalogue of Nebulae and Clusters of Stars, published the same year.
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