Cetus, the Sea Monster, is a southern constellation that is visible in the fall. It is also often called the Whale. Hold your mouse cursor over the image to see constellation figures, boundaries, and star identifications. Cetus is located in the region of the sky called the "Sea" or the "Water" that is home to Aquarius (the Water Bearer), Pisces (the Fishes) and Eridanus (the River), which are all water-related constellations. Although Cetus is not technically an ecliptic constellation because the line of the ecliptic does not actually go through it, the ecliptic lies just 8.5 arcminutes away from one of its northwest corners. Because the Sun subtends an apparent angle of 30 arcminutes, part of the Sun does pass through that corner of Cetus. This currently occurs on March 27 and March 28. The planets can also pass through Cetus. In Greek mythology, Cetus is the sea monster who was killed by Perseus when he rescued the Princess Andromeda, who had been chained to a rock for the monster. Andromeda's mother, the queen Cassiopeia, had angered Poseidon, the sea god, by claiming that Andromeda was more beautiful than Poseidon's Nereids, the sea nymphs. To appease Poseidon, Cassiopeia and her husband Cepheus, the king, had to sacrifice Andromeda to Cetus, who had been sent by Poseidon to ravage their land. Andromeda was rescued by Perseus, who happened to be passing by. Perseus later married Andromeda. Beta Ceti is Deneb Kaitos. It is the brightest star in the constellation of Cetus. Deneb Kaitos means the " southern tail of Cetus" or the "whale's tail." It is also known by the name Diphda, which means the "second frog." Fomalhaut is the "first frog." Beta Ceti shines with an apparent magnitude of 2.04 and is located 96 light-years from the Earth. It is a spectral-class K type star. Alpha Ceti is Menkar. It shines at magnitude 2.45 and is located 220 light-years away. It is a spectral-type M red-giant star that is also a wide optical double star with 93 Ceti, a blue-white magnitude 5.6 star that is 16 arcminutes to the north of Menkar. The name Menkar means the "nose" of the sea monster or whale. Zeta Ceti is Baten Kaitos, which means the "belly of the sea monster." It is a magnitude 3.9 spectral-type K star that is located 260 light-years away. Omicron Ceti is Mira, the first variable star to be discovered. Its brightness varies over a period of 332 days from magnitude 3, where it is visible to the unaided eye, to magnitude 10, when it disappears to unaided vision. Mira is a pulsating variable red-giant with a spectral class of type M, which is located 420 light-years from Earth. Mira's diameter oscillates in size between 400 and 500 solar diameters. It was discovered by David Fabricius in 1596. Mira is the prototype for the Mira class of variable stars, all oscillating red giants. Johannes Hevelius named the star Mira, which means "wonderful" in Latin. Mira has a white-dwarf companion called Mira B, which is accreting mass from the red giant. Tau Ceti is a star similar to our own Sun. It shines at magnitude 3.5, and is a spectral-class G star that is located 11.9 light-years away. It is the nearest Sun-like star but has a luminosity of only 55 percent of the Sun. Cetus contains only one Messier object, galaxy M77, which is located 50 arcminutes southeast of Delta Ceti. M77 is also close to NGC 1055, another bright spiral galaxy that is only 1/2 degree to its north-northwest. Several other interesting deep-sky objects are also located in Cetus, including the large planetary nebula NGC 246, and spiral galaxy NGC 247. Cetus was originally cataloged by the Greek astronomer Ptolemy in the 2nd century C.E. It is the 4th largest of today's 88 modern constellations, covering 1231 square degrees of sky. North is to the top in the above image.
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