The Grus Constellation

Grus is a constellation in the southern sky. Its name is Latin for the crane. 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 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 Bayer designations to its stars in 1756, some of which had been previously considered part of the neighbouring constellation Piscis Austrinus. The constellations Grus, Pavo, Phoenix and Tucana are collectively known as the “Southern Birds.” Grus is bordered by Piscis Austrinus to the north, Sculptor to the northeast, Phoenix to the east, Tucana to the south, Indus to the southwest, and Microscopium to the west. Covering 366 square degrees, it ranks 45th of the 88 modern constellations in size and covers 0.887% of the night sky. 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 21^h 27.4^m and 23^h 27.1^m, while the declination coordinates are between −36.31° and −56.39°. Grus is located too far south to be seen by observers in the British Isles and the northern United States, though it can easily be seen from Florida or California; the whole constellation is visible to observers south of latitude 33°N.

Grus has several bright stars. Marking the left wing is Alpha Gruis, 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 (although the Arabians saw it as the brightest star in the Fish’s tail, as Grus was then depicted). Alnair is around 380 times as luminous and has over 3 times the diameter of the Sun. Lying 5 degrees west of Alnair, denoting the Crane’s heart is Beta Gruis, a red giant of spectral type M5III. It has a diameter of 0.8 astronomical units 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 has begun cooling and expanding, which will see it transform into a red giant.

Nicknamed the spare-tyre nebula, IC 5148 is a planetary nebula located around 1 degree west of Lambda Gruis. Around 3000 light-years distant, it is expanding at 50 kilometres a second, one of the fastest rates of expansion of all planetary nebulae. Northeast of Theta Gruis is 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 arcminutes 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 7552 and 7582 are exhibiting high starburst activity; this is thought to have arisen because of the tidal forces from interacting. Located on the border of Grus with Piscis Austrinus, IC 1459 is a peculiar E3 giant elliptical galaxy. It has a fast counterrotating stellar core, and shells and ripples in its outer region. The galaxy has an apparent magnitude of 11.9 and is around 80 million light years distant. NGC 7424 is a barred spiral galaxy with an apparent magnitude of 10.4. located around 4 degrees west of the Grus Triplet. Approximately 37.5 million light years distant, it is about 100,000 light years in diameter, has well defined spiral arms and is thought to resemble the Milky Way. Two ultra-luminous X-ray sources and one supernova have been observed in NGC 7424. SN 2001ig was discovered in 2001 and classified as a Type IIb supernova, one that initially showed a weak hydrogen line in its spectrum, but this emission later became undetectable and was replaced by lines of oxygen, magnesium and calcium, as well as other features that resembled the spectrum of a Type Ib supernova. A massive star of spectral type F, A or B is thought to be the surviving binary companion to SN 2001ig, which was believed to have been a Wolf–Rayet star. Located near Alnair is NGC 7213, a face-on type 1 Seyfert galaxy located approximately 71.7 million light years from Earth. It has an apparent magnitude of 12.1. Appearing undisturbed in visible light, it shows signs of having undergone a collision or merger when viewed at longer wavelengths, with disturbed patterns of ionized hydrogen including a filament of gas around 64,000 light-years long. It is part of a group of ten galaxies. 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. Credit: Wikipedia.