Crater (“the cup”) is one of the original constellations first recorded by Greek astronomer Ptolemy in his astronomical treatise called Almagest around 150 AD. This southern constellation is rather faint with its brightest star, Labrum, an orange giant located 196 light years away with a visual magnitude of just 3.56.
Crater is the 53rd largest constellation in the night sky, and can be seen by observers located between +65° and -90° of latitude, although best seen from March to June. Consisting of only dim stars, Crater is difficult to find, but fortunately the constellation of Corvus situated to its east is easy to spot, with Crater and Corvus subsequently located south of Leo and Virgo, and north of Hydra.
Crater is a member of the Hercules family of constellations, together with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crux, Cygnus, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Sextans, Serpens, Triangulum Australe, and Vulpecula.
According to Greek legend, Apollo needed water in order to perform a ritual sacrifice, and so sent a crow or raven equipped with a cup to a nearby spring. During its journey, however, the bird proceeded to gorge itself on the fruit of a fig tree, and as an excuse for its tardiness brought back a water snake which it blamed for blocking access to the spring. Seeing through its lies, Apollo flung the crow, cup, and snake into the sky, which then became the constellations of Crater (cup), Corus (crow), and Hydra (water snake). Apollo also condemned the crow to eternal thirst, and the bird has had a distintive dry sounding caw ever since.
– Labrum (Delta Crateris), the constellation’s brightest star, is an orange giant located 196 light years away with a visual magnitude of 3.56. Compared to the Sun, it is 21 times bigger, 2.5 times more massive, and 175 times more luminous. The star’s name Labrum means “the Lip” in Latin, referring to the lip of the Holy Grail from which Jesus and his disciples drank wine from at the Last Supper.
– Alkes (Alpha Crateris), the second brightest star in Crater, is an orange giant found 174 light years from our solar system with a visual magnitude of 4.07. Its is 13 times bigger than our sun, 2.5 times more mass, and is 80 times more luminous. Alkes” means “the wine cup” in Arabic.
– Gamma Crateris, the constellation’s third brightest star, is a double system 84 light years distant whose primary component is a white dwarf (A9V). Gamma Crateris shines with a visual magnitude of 4.05.
Other stars of interest in Crater includes the white sub-giant Al Sharasif (Beta Crateris) found 266 light years away with a magnitude 4.48; as well as the blue dwarf star Theta Crateris; the white giant star Eta Crateris; the yellow giant star Zeta Crateris; and the orange giant star Epsilon Crateris.
Notable Deep Sky Objects
There are no Messier objects in Crater, although it does contain a number of interesting deep sky objects, including the spiral galaxies NGC 3511 and NGC 3981; and the barred-spiral galaxy NGC 3887. Crater also contains the following astronomical objects:
– RX J1131-1231 is a quasar located around 6 billion light years distant with a supermassive black hole at its centre spinning at more than half the speed of light. Its rapid rotation would suggest that the quasar grew through a merger with another galaxy, rather than by pulling in space material which would likely result in a much slower rate of spin. Gravitational lensing caused by an elliptical galaxy located between RX J1131-1231 and the Earth has created four images of the same quasar, which appears as pink in the photo.
– Crater 2 is a dwarf galaxy that is around 6,500 light-years across, and situated around 391,000 light-years from Earth. It is the fourth closest satellite galaxy orbiting our own Milky Way, behind the Large Magellanic Cloud, the Small Magellanic Cloud, and the Sagittarius dwarf galaxy. Despite radiating 160,000 times more light than our sun, it lay undiscovered until 2016 as its stars are so stretched out that it was impossible to resolve them as forming part of a single galaxy.