Grus is one of the twelve constellations that was created by Dutch astronomer Petrus Plancius in the late 16th Century, and subsequently incorporated by the German celestial cartographer Johann Bayer’s into his sky atlas called Uranometria in 1603. Meaning “the crane” in Latin, Grus belongs to a grouping of constellations which together with Pavo (peacock), Tucana (toucan) and Phoenix are collectively called the “Southern Birds”. The constellation of Grus does have one claim to legend, though, namely that in Greek mythology the crane was sacred to the god Hermes. The brightest star in Grus is Alnair, a blue-white subgiant located around 101 light years away from our sun which shines with an apparent magnitude of 1.74.
Grus is a southern sky constellations that is visible to observers located from between +34° and -90° of latitude. It is the 45th largest constellation, and in the northern hemisphere is best seen during Autumn in the early evening. Bordering Grus is the constellation Piscis Austrinus (north), Sculptor (northeast), Phoenix (east), Tucana (south), Indus (southwest), and Microscopium (west).
Johann Bayer Constellation Family
Grus is a member of the Johann Bayer family of constellations, together with Apus, Chamaeleon, Dorado, Hydrus, Indus, Musca, Pavo, Phoenix, Tucana and Volans.
– Alnair (Alpha Gruis), the constellation’s brightest star, is a red giant located around 101 light years from our solar system with a visual magnitude of 1.74. It is estimated to be around 100 million years old, and compared to our sun is about 4 times more massive, and 380 times more luminous. It also has a rotational velocity of around 215km/s, and has a dust disk in orbit around it due to its excessive rotation. The constellation of Grus was originally created from stars that hailed from a southern constellation known as Piscis Austrinus, and the star name Alnair derives from an Arabic phrase meaning “the bright one from the fish’s tail”.
– Gruid (Beta Gruis), the constellation’s second brightest, is a stunning red giant with an M5 III stellar classification. It is located 177 light years from the Sun, and shines with visual magnitude of 2.146, although it is actually a semi-regular variable whose luminosity varies by around 0.4 over a period of 37-days. Gruid has 2.4 times the mass of our sun, 180 times its radius, and is 1,500 times more luminous.
– Al Dhanab (Gamma Gruis), the constellation’s third brightest star, is a blue-white subgiant with a B8 III spectral classification. It is located 211 light years distant, and is about 390 times more luminous than our own sun, giving it a visual magnitude of 3.003 as seen from Earth. Al Dhanab has an estimated rotational velocity of 57km/s, making it a semi-rapid rotator, with our sun, by comparison, having an azimuthal velocity of just 2km/s.
Amongst the other notable stars in the constellation is Delta Gruis, a binary star with a visual magnitude of 3.97 consisting of a yellow giant (G7III) and a red giant (M4.5III) located some 325 light-years away. There is also Tau-1 Gruis, a yellow dwarf (G0V) type star with a visual magnitude of 6.03 around 108.58 light years away; and Gliese 832, a red Dwarf (M1.5V) with a visual magnitude of 8.66 found a mere 16.1 light years from our solar system.
Notable Deep Sky Objects
While Grus has no Messier objects, it does contain several deep-sky objects that are so dim that they can only be seen using larger telescopes.
– NGC 7424 is a barred spiral galaxy that has an apparent visual magnitude of 10.4. It is found 37.5 million light-years from Earth, and is about 100,000 light-years across, making it similar in size to our own Milky Way. So far, two Ultraluminous X-ray sources (ULXs) emitting incredible amounts of X-rays have been discovered in NGC 7424, as well as a Type Ib supernova, which at one stage shone with a brightness one-third of the whole galaxy.
– NGC 7213 is an example of a Seyfert galaxies, which are huge active galaxies with very high levels of surface brightnesses. It is situated around 71.7 million light years distant, and shines with an apparent magnitude of 12.1.
– Spare-tyre Nebula (IC 5148), a planetary nebula situated 3,000 light-years away, that continues to expand at a rate of 50km/s, making it one of the fastest expanding nebulae of its type.
Other notable galaxies in the constellation include an interacting group called the Grus Quartet (NGC 7552, NGC 7590, NGC 7599, NGC 7582); and also a spiral galaxy located 122 million light years away called NGC 7410, that shines with a visual magnitude of 11.7.