Star Constellation Facts: Cetus

Star Constellation Facts: Cetus

Cetus, the “Sea Monster”, is the fourth biggest constellation in the night sky, and is best observed in Winter by observers located between latitudes of +70 and -90 degrees. The constellation contains only one Messier object, a large galaxy called M77, but is home to several notable stars, among which is Omicron Ceti, a variable star that defines an entire class of variable stars, as well as 14 stars with confirmed planets.


Menkar, the star depicting the head of Cetus is found near the constellation of Taurus, with its long body then stretching all the way across a part of the sky referred to as “The Sea”. There are found a group of other constellations evoking watery images, including Eridanus (a river), Aquarius (the water bearer), and Pisces (fish), Piscis Austrinus (southern fish), Capricornus (sea-Goat), and Aquarius (water-carrier).


Cetus (“the Whale”) most commonly represents a sea-monster that was sent to devour Andromeda, after her mother Cassiopeia foolishly claimed that her daughter was more beautiful than the Nereids. The story goes that Poseidon, the sea-god, was so incensed by Cassiopeia that he sent a sea monster to destroy the lands belonging to Andromeda’s father, King Cepheus. To ward off disaster, Poseidon ordered the King and Queen sacrifice their daughter to the sea monster, but before the monster could devour the princess, the young hero Perseus happened by, and rescued the princess after killing the monster.

Notable Stars

– Alpha Ceti (Menkar, Menkab); represents the ‘Nose of the Whale’, and is a red giant star (M1.5IIIa) located 220 lights year from Earth. It has a magnitude of 2.54, making it the second brightest star in Cetus.

– Deneb Kaitos (Diphda, Beta Ceti), located about 94 light years away, is the most luminous star in Cetus, with an apparent visual magnitude of 2.04. Deneb Kaitos is an orange giant star (K0 III), meaning that it has evolved off the main sequence, and is Star Constellation Facts: Cetusrapidly turning into a red giant. One of its traditional names, Deneb Kaitos, derives from the Arabic for “the southern tail of Cetus”. Its other traditional name, Diphda, comes from the Arabic for “the second frog”, to distinguish it from the star Fomalhaut in the constellation of Piscis Austrinus, which is sometimes referred to as “the first frog.”

– Mira (Omicron Ceti); a 6 billion years old red giant (M7 IIIe) located 420 light years distant, and one component of a binary system. It is also an oscillating variable star that defines an entire class of stars, known as Mira variable stars. There are between 6,000, and 7,000 stars in this class, all of which are red giants with surfaces that oscillate in a way that produces variations in their luminosities that can stretch from about 80 days, to periods of more than 1,000 days.

Mira B, on the other hand, is a hot white dwarf that is busy pulling material off Mira A, thus forming the closest symbiotic binary system to the Sun. It is interesting to note that Mira A is shedding material as it moves through space. The Galaxy Evolution Explorer space telescope has revealed a 13-light year-long trail of stellar material behind the star.

– Tau Ceti; a rather unremarkable yellow dwarf star (G8.5 V) located only 11.9 light years away, and with an apparent magnitude of 3.5. It has about 80% of the Sun’s mass, and only 55% of the its brightness. What distinguishes it from other, perhaps more deserving Sun-like stars is that fact that along with Epsilon Eridani in the constellation Eridanus, it was chosen for a ground-breaking SETI experiment, Project Ozma, in 1960. Frank Drake of Cornell University ran Project Ozma in an attempt to discover artificial, (i.e. intelligent) radio signals, but despite his best attempts, he did not find anything that even remotely sounded like an alien communication.

Notable Deep Sky Objects

– Messier 77 (M77, NGC 1068); located about 47 million light years away, M77 is a large barred spiral galaxy with a diameter of about 170,000 light years, giving it an apparent visual magnitude of 9.6. M77 was discovered in 1780 by Charles Messier’s associate, Pierre Méchain, who described it as a nebula, while Messier and William Herschel both described the object as a large cluster of stars. M77 is a known radio source due to its active nucleus, which is obscured by dense intergalactic dust. Look for M77 0.7 degrees east-south-eastward of Delta Ceti.

– NGC 1055; another radio source, NGC 1055 is only 0.5 degrees removed from M77. It is oriented nearly edge-on to our line of sight, and with a diameter of about 115,800 light years, it is the largest member of a cluster of galaxies that includes N1073 and some smaller, irregular galaxies.

– NGC 1087; although classified as an intermediate spiral, NGC 1087 it is difficult to discern any spiral structure in visible light. The only detail that is clearly defined in this image is the small central bar, and the many irregular features that make up the body of the galaxy, such as the extremely small nucleus. NGC 1087 is about 80 million light years away.

Meteor Showers

Three meteor showers are associated with Cetus- the Omicron Cetids, the Eta Cetids, and the October Cetids, none of which is particularly productive.

– The Omicron Cetids; one of a few daylight showers, the Omicron Cetids shower runs from about May 7th to about June 9th, with a peak that can occur at any time during the period from May 14th to 25th. Daylight makes the meteors in this stream all but invisible, but suitable radio-echo equipment could potentially reveal up to 18 meteors per hour during the peak period.

– The Eta Cetids; while this shower has a long duration, from about September 20th to about November 2nd, activity is for the most part almost non-existent, although large fireballs have been known to occur unexpectedly at any time between the stated dates. The Eta Cetids normally peak during the first week of October.

– The October Cetids; the highest meteor count in this shower happened in 1916, when the peak rate reached 4 meteors per hour. The peak date is not certain, and it is recommended that optical aid be used to spot meteors between October 20th to about October 25th/26th.