The Crater Constellation

Posted on Friday, 13 April, 2018 by Zheluo Cai

The Crater is a small constellation in the Southern Celestial Hemisphere. Its name means “cup” in Latin. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it has been associated with the god Apollo and is perched on the back of Hydra, the water snake. Covering 282.4 square degrees and hence 0.685% of the sky, Crater ranks 53rd of the 88 constellations in area. It is bordered by Leo and Virgo to the north, Corvus to the east, Hydra to the south and west, and Sextans to the northwest. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of six segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 10^h 51^m 14^sand 11^h 56^m 24^s, while the declination coordinates are between −6.66° and −25.20°. Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 65°N.

The German cartographer Johann Bayer used the Greek letters Alpha, through Lambda to label the most prominent stars in the constellation. Bode added more, though only Psi Crateris remains in use. Within the constellation’s borders, there are 33 stars brighter than or equal to apparent magnitude 6.5. The three brightest stars—Delta, Alpha and Gamma Crateris—form a triangle nearby the brighter star Nu Hydrae in neighbouring Hydra. Delta Crateris is the brightest star in Crater at magnitude 3.6. 186 ± two light-years away. It is an orange giant star of spectral type K0III that is 1.0–1.4 times as massive as the Sun. An ageing star, it has cooled and expanded to 22.44 ± 0.28 times the Sun’s radius. It is radiating 171.4 ± 9.0 as much luminosity as the Sun from its outer envelope at an effective temperature of 4,408 ± 57 K. Traditionally called Alkes “the cup,” Alpha Crateris is an orange-hued star of magnitude 4.1, 159 ± two light-years from Earth. With an estimated mass around 1.61 times that of the Sun, it has exhausted its core hydrogen and expanded to 12 or 13 times the Sun’s diameter, shining with 69 times its luminosity. And a surface temperature of 4645 K. With an apparent magnitude of 4.5, Beta Crateris is a binary system, consisting of a white-hued star of spectral type A1III and a white dwarf of spectral type DA1.4, 340 ± 20 light-years from Earth. The Hubble Space Telescope was unable to make out the two stars as separate objects. Gamma Crateris is a double star divisible in small amateur telescopes. The primary is a white main sequence star of spectral type A7V that is an estimated 1.81 times as massive as the Sun, while the secondary—of magnitude 9.6—has 75% the Sun’s mass, and is likely an orange dwarf. Located near Alkes is the red-hued R Crateris, a semiregular variable star of type SRb and a spectral classification of M7. It has a magnitude of 9.8-11.2 and an optical period of 160 days. SZ Crateris is a magnitude 8.1 variable star. It is a nearby star system located about 44 light years from the Sun. It is also identified as Gliese 425, and in the past, it was known as Abt’s Star.

HD 98800, also known as TV Crateris, is a quadruple star system with two pairs of young stars. One pair has a debris disk orbiting the both. HD 96167 is a yellow subgiant that was found to have a planet in 2009. HD 98649 is a sun-like star with a planet in an eccentric orbit. BD-10°3166 is a metallic orange main sequence star that was found to have a planet. DENIS-P J1058.7-1548 is a brown dwarf.

The Crater 2 dwarf galaxy is a satellite galaxy of the Milky Way, located approximately 380,000 ly from Earth. NGC 3511 is a spiral galaxy with a slight bar, seen nearly from the edge, of type SBbc. It is a member of the galaxy cluster Abell 1060. This galaxy is magnitude 12 and is 4′ × 1′ in size. Right nearby, 30″ away, is NGC 3513, another SB-class spiral. NGC 3887 is a barred-spiral galaxy of type SBc, magnitude 11, with a diameter of 3.5′. NGC 3981 is a spiral galaxy with two wide spiral arms, of type SBbc. It is magnitude 12 with a diameter of 3′. This galaxy was discovered by William Herschel in 1785. RX J1131 is a quasar located 6 billion light-years away from Earth. The black hole in the centre of the quasar was the first black hole whose spin has ever been directly measured. Credit: Wikipedia.