|Pronunciation||//, or colloquially //; genitive //|
|Right ascension||22 h|
|Area||366 sq. deg. (45th)|
|Stars with planets||6|
|Stars brighter than 3.00m||3|
|Stars within 10.00 pc (32.62 ly)||1|
|Brightest star||α Gru (Alnair) (1.73m)|
|Nearest star||Gliese 832
(16.11 ly, 4.94 pc)
|Visible at latitudes between +34° and −90°.
Best visible at 21:00 (9 p.m.) during the month of October.
Grus (//, or colloquially //) is a constellation in the southern sky. Its name is Latin for the crane, a species of bird. It is one of twelve constellations conceived by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. Grus first appeared on a 35-cm (14 in) diameter celestial globe published in 1598 in Amsterdam by Plancius and Jodocus Hondius and was depicted in Johann Bayer's star atlas Uranometria of 1603. French explorer and astronomer Nicolas Louis de Lacaille gave its stars Bayer designations in 1756. The constellations Grus, Pavo, Phoenix and Tucana are collectively known as the "Southern Birds".
The constellation's brightest star, Alpha Gruis, is also known as Alnair and appears as a 1.7-magnitude blue-white star. Beta Gruis is a red giant variable star with a minimum magnitude of 2.3 and a maximum magnitude of 2.0.
The stars that form Grus were originally considered part of Piscis Austrinus (the southern fish). The Arabic name of Beta Gruis (al-tizini, "the rear one") and Gamma Gruis (al-dhanab, "the tail") reflect this origin.
The stars were first defined as a separate constellation by Petrus Plancius, who created twelve new constellations based on the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. Grus first appeared on a 35-cm diameter celestial globe published in 1597 (or 1598) in Amsterdam by Plancius with Jodocus Hondius. Its first depiction in a celestial atlas was in Johann Bayer's Uranometria of 1603.
Grus represents a crane, though it is sometimes seen as a flamingo. There are no ancient myths associated with Grus, except for those involving Piscis Austrinus, with which it was previously joined.
The stars that correspond to Grus cannot all be seen from China. In Chinese astronomy some of them are located in the Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ), while the rest were placed among the Southern Asterisms (近南極星區, Jìnnánjíxīngqū) by Xu Guangqi, based on knowledge of western star charts.
Grus is bordered by Piscis Austrinus to the north, Sculptor to the northeast, Phoenix to the east, Tucana to the south, Microscopium to the west, and Indus to the southwest. Covering 366 square degrees, it ranks 45th of the 88 modern constellations in size and covers 0.916% of the night sky. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Gru". The official constellation boundaries, as set by Eugène Delporte in 1930, are defined as a polygon of 6 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 21h 27.4m and 23h 27.1m, while the declination coordinates are between −36.31° and −56.39°.
Although he depicted Grus on his chart, Bayer did not assign its stars Bayer designations. French explorer and astronomer Nicolas Louis de Lacaille labelled them Alpha to Phi in 1756 with some omissions. In 1879, American astronomer Benjamin Gould added Kappa, Nu, Omicron and Xi, which had all been catalogued by Lacaille but not given Bayer designations. Lacaille considered them too faint, while Gould thought otherwise. Xi Gruis had originally been placed in Microscopium. Conversely, Gould dropped Lacaille's Sigma as he thought it was too dim.
Grus has several bright stars. Alpha Gruis, called Alnair, is a blue-white star of spectral type B6V and apparent magnitude 1.7, around 101 light-years from Earth. Its traditional name, Alnair, means "the bright one" and refers to its status as the brightest star in Grus. In reality it is around 380 times as luminous and has over three times the diameter of the Sun. Lying 5 degrees west of Alnair, Beta Gruis is a red giant of spectral type M5III. It has a diameter of 0.8 AU (if placed in the Solar System it would extend to the orbit of Venus) located around 170 light-years from Earth. It is a variable star with a minimum magnitude of 2.3 and a maximum magnitude of 2.0.
Lying in the northwest corner of the constellation and marking the crane's eye is Gamma Gruis, a blue-white subgiant of spectral type B8III and magnitude 3.0 lying around 211 light-years from Earth. Also known as Al Dhanab, it has finished fusing its core hydrogen and begun cooling and expanding, which will see it transform into a red giant.
There are several naked-eye double stars in Grus. Delta Gruis (δ Gru), composed of Delta1 Gruis (δ1 Gru) and Delta2 Gruis (δ2 Gru), is an optical double. which forms a trangle with Alnair and Beta. Delta1 is a yellow giant of magnitude 4.0, 296 light-years from Earth, and Delta2 is a red giant of magnitude 4.1, 325 light-years from Earth. The two are 45 seconds apart. Mu Gruis (μ Gru), composed of Mu1 Gruis (μ1 Gru) and Mu2 Gruis (μ2 Gru), is also an optical double. Mu1 is the brighter of the two at magnitude 4.8 - it is 262 light-years from Earth - and Mu2 the dimmer at magnitude 5.is 240 light-years from Earth. Pi Gruis, an optical double with a variable component, is composed of Pi1 Gruis and Pi2. Pi1 is a semi-regular red giant with a minimum magnitude of 6.7 and a maximum magnitude of 5.4. It has a period of 150 days and is 500 light-years from Earth. Pi2 is a white giant 132 light-years from Earth and is often brighter than its companion at magnitude 5.6. Theta Gruis is yet another double star, lying 5 degrees east of Delta1 and 2.
Five star systems are thought to have planets. Tau1 Gruis is a yellow star of magnitude 6.0 located around 106 light-years away. Either a main sequence star or just beginning to enlarge and cool off it, it was found to have a planetary companion in 2002.
Northeast of Theta Gruis (θ Gru) are four interacting galaxies known as the Grus Quartet. These galaxies are NGC 7552, NGC 7590, NGC 7599, and NGC 7582. The latter three galaxies occupy an area of sky only 10' across and are sometimes referred to as the "Grus Triplet," although all four are part of a larger loose group of galaxies called the IC 1459 Grus Group.
NGC 7424 is a barred spiral galaxy with an apparent magnitude of 11.0. It is approximately 37.5 million light years distant. The galaxy is about 100,000 light years in diameter and has well defined spiral arms, so it is called a “grand design” galaxy. Two ultraluminous X-ray sources and one supernova have been observed in NGC 7424.
SN 2001ig, one of the two supernovas within NGC7424, was discovered in 2001 and classified as a Type IIb supernova, one that initially shows a weak hydrogen line in its spectrum, but whose H emission later becomes undetectable and is replaced by lines of oxygen, magnesium and calcium, as well as other features that resemble the spectrum of a Type Ib supernova.
NGC 7213 is a face-on, type 1.5 Seyfert galaxy lying about 16′ to the southeast of Alpha Gruis. It is one of the brightest spiral galaxies in Grus and approximately 71.7 million light years from Earth.
NGC 7410 is a spiral galaxy discovered by British astronomer John Herschel during observations at the Cape of Good Hope in October 1834. The galaxy has a visual magnitude of 11.7 and is approximately 122 million light years distant from Earth. During that same period, Herschel also discovered two other galaxies in Grus: NGC 7418, a barred spiral galaxy with an apparent visual magnitude of 10.9, and NGC 7421, another barred spiral galaxy with an apparent visual magnitude of 11.7.
IC 1459 is a large peculiar elliptical galaxy. It has a fast counterrotating stellar core, shells and ripples. The galaxy has an apparent visual magnitude of 10.97 and is 68.8 million light years distant.
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- Obsolete Constellations: Phoenicopterus
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- http://www.atnf.csiro.au/people/bkoribal/ngc7582/grus_hi.html. Missing or empty
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- Ridpath, Ian; Tirion, Wil (2001), Stars and Planets Guide, Princeton University Press, ISBN 0-691-08913-2
|Wikimedia Commons has media related to:|
- The Deep Photographic Guide to the Constellations: Grus
- Starry Night Photography - Grus Constellation