Crater (the Cup) is a small, faint constellation in the southern celestial sky, positioned between Corvus and Leo and resting above the long body of Hydra. Its stars form a rough cup-shaped outline, although none is particularly bright.
Crater is one of the 48 classical constellations recorded by the Greek astronomer Ptolemy in the second century AD. It is best known for its mythology involving Apollo’s raven and the Water Snake, but it also contains several distant galaxies and an unusual gravitationally lensed quasar.
Where Is Crater and When Can You See It?
Crater is the 53rd-largest constellation, covering approximately 282 square degrees of sky. It lies immediately west of Corvus and north of Hydra, with Leo and Virgo farther north.
The best time to observe Crater is March through June, particularly April, when it is well placed in the evening sky. From most of the United States, Crater is visible in the southern sky during spring evenings. It appears higher above the horizon from southern states, making its faint stars easier to identify.
To find it, first locate the more distinctive four-sided pattern of Corvus. Crater lies immediately to its west, above the winding outline of Hydra.
Its brightest stars form a loose, irregular cup, but a star chart is helpful because most are only fourth magnitude.
Mythology of Crater
In Greek mythology, Crater represents the cup carried by a raven belonging to the god Apollo.
According to the story, Apollo sent the bird to fetch water from a spring. On its journey, however, the raven discovered a fig tree and waited for its fruit to ripen before eating its fill. Realizing it had delayed too long, the raven returned with a water snake and claimed that the creature had prevented it from reaching the spring. Apollo saw through the deception and placed all three figures in the heavens: Crater as the cup, Corvus as the raven, and Hydra as the water snake.
In one version of the myth, Apollo also condemned the raven to perpetual thirst, explaining why the bird’s call sounds so harsh.
The three constellations remain close together in the sky, preserving their mythological connection.
Notable Stars in Crater
- Labrum (Delta Crateris) – The brightest star in Crater, an orange giant approximately 195 light-years away, shining at magnitude 3.6. It is substantially larger and more luminous than the Sun. Its Latin name refers to the rim or lip of a vessel, fitting its position in the celestial cup.
- Alkes (Alpha Crateris) – An orange giant approximately 175 light-years away, with an apparent magnitude around 4.1. Its name comes from an Arabic word associated with a cup or drinking vessel.
- Gamma Crateris – A binary star system approximately 85 light-years away, shining at magnitude 4.1. Its brighter component is a white A-type main-sequence star, accompanied by a fainter star that can be resolved with suitable telescopes.
- Al Sharasif (Beta Crateris) – An evolved white star approximately 265 light-years away, with an apparent magnitude around 4.5.
- Theta Crateris – A blue-white main-sequence star of approximately fourth magnitude, located in the southern part of the constellation.
Crater contains no stars brighter than third magnitude, making it one of the less conspicuous classical constellations.
Notable Deep-Sky Objects in Crater
Crater contains no Messier objects, but it is home to several spiral galaxies, a distant quasar, and one of the Milky Way’s unusually diffuse satellite galaxies.
NGC 3981 — A Distorted Spiral Galaxy
NGC 3981 is a spiral galaxy approximately 65 million light-years away, with an apparent magnitude around 11. Its sweeping spiral arms appear somewhat distorted, possibly reflecting past gravitational interactions with neighboring galaxies.
Long-exposure photographs reveal a bright central region surrounded by delicate arms containing stars, gas, and dust.
Although too faint for binoculars, NGC 3981 can be observed with moderate to large amateur telescopes under dark skies.
NGC 3887 — A Barred Spiral Galaxy
NGC 3887 is a barred spiral galaxy approximately 60 million light-years away. It has a bright central bar surrounded by spiral arms, a structure common among galaxies throughout the universe.
Its relatively low surface brightness makes it a challenging target for smaller telescopes, but long-exposure photographs reveal its structure clearly.
Other galaxies in Crater include NGC 3511, another spiral system visible with larger amateur instruments.
RX J1131−1231 — A Gravitationally Lensed Quasar
RX J1131−1231 is a distant quasar whose light has been distorted by the gravity of a foreground galaxy. The quasar is powered by matter falling toward a supermassive black hole in the center of an active galaxy billions of light-years away.
As its light travels toward Earth, it passes near another galaxy whose gravity bends and magnifies the light, producing four apparent images of the same quasar. This phenomenon, known as gravitational lensing, allows astronomers to study extremely distant objects and investigate the distribution of matter in galaxies.
Observations of RX J1131−1231 have also helped researchers study the properties of the black hole powering the quasar.
Crater 2 — An Exceptionally Diffuse Dwarf Galaxy
Crater 2 is a dwarf spheroidal galaxy discovered in 2016, located approximately 380,000 light-years from Earth. It is a satellite of the Milky Way, but unlike many compact dwarf galaxies, its stars are spread across an unusually large area.
Despite its substantial physical size, Crater 2 is extraordinarily faint because its stellar population has such low surface brightness. This makes it extremely difficult to detect against the background sky and explains why astronomers only identified it relatively recently.
Crater 2 is especially interesting to researchers studying the evolution of dwarf galaxies and the gravitational influence of dark matter.