Caelum (“the chisel”) is one of the smallest, faintest constellations in the night sky, and is one of 14 southern constellations invented by French astronomer Abbé Nicolas Louis de Lacaille in the mid-18th century. Its brightest star, Alpha Caeli, is a binary system situated 65.7 light years from Earth with an apparent magnitude of 4.44.
Caelum is the 8th smallest of the 88 recognized constellations, taking up an area of just 125 square degrees of the southern celestial heavens. It can be seen by observers located between +40° and -90° of latitude, although best viewed during the month of January. The constellations bordering Caelum includes Columba to its east, Horologium and Eridanus to its west, Dorado and Pictor to its south, and Lepus to its north.
Lacaille Constellation Family
Caelum is a member of the Lacaille family of constellations, together with Antlia, Circinus, Fornax, Horologium, Mensa, Microscopium, Norma, Octans, Pictor, Reticulum, Sculptor, and Telescopium.
– Alpha Caeli, the constellation’s brightest star, is a binary star located 65.7 light years from our solar system that shines with an apparent magnitude of 4.44. Its primary component, Alpha Caeli A, is a blue-white dwarf (F2V) that has around 1.5 times the Sun’s size and mass, and 5.2 times its luminosity, while its fainter companion, Alpha Caeli B, is a red dwarf (M0.5V) with 0.3 solar masses, and a luminosity just 1% that of our sun.
– Gamma Caeli, the second brightest star in Caelum, is a multiple star system situated 185 light years distant of magnitude 4.55. Its primary binary component, Gamma-1 Caeli, consists of an orange giant (K3III) and a fainter white giant companion; while further away is Gamma-2 Caeli, another binary system composed of a yellow-white giant and a fainter blue-white subgiant (F2IV/V) companion star.
– Beta Caeli, the constellation’s third brightest star, is a yellow-white dwarf (F2V) found 90.2 light years away of magnitude 5.04. It is 1.84 times bigger than the Sun, and around 6 times brighter.
Other stars of interest in Caelum includes the blue-white subgiant Delta Caeli, the yellow-white dwarf Nu Caeli, the orange sub-giant Zeta Caeli, and the red giant Lambda Caeli.
Notable Deep-Sky Objects
This diminutive constellation is located away from the Milky Way‘s plane, and as such contains no Messier objects, and very few deep-sky objects of any interest. This includes the barred spiral galaxy IC 2106 found 229 million light years distant of magnitude 13; the barred spiral galaxy NGC 1679 located 48 million light years away of magnitude 13.1; and NGC 1571, another galaxy with an apparent magnitude of 12.3.
– HE0450-2958 is a quasar, or the supermassive black hole that usually forms at the centre of a galaxy. In the case of this quasar, however, there does not seem to be any galaxy associated with its formation, although recent studies have suggested that it may have a host galaxy that is hard to resolve behind the quasar’s bright light. HE0450-2958 lies 3 billion light years from our solar system, with one of the hot jets of energy and matter shooting out from it pointing at and boosting the star formation in a companion galaxy.