Cetus


Transit Date of principal star:
6 November


Although Cetus is supposed to be a whale, from antiquity the constellation was considered to be the monster about to devour Andromeda before Perseus could come to the rescue.

Johann Bayer, for example, incorporated the idea in his depiction of the beast -- a toothy monster far removed from one's idea of a peaceful beluga or hump-back.

In fact there are many stories of sea monsters in older cultures, such as Tiamat, the Babylonian dragon which represented the female principle of Chaos. It is perhaps no surprise that some of the larger constellations refer to mythic (or at least pretty horrific beasts) -- Draco, Serpens, Hydra, and Cetus.


Cetus' stars are quite faint, but there are a few well known stars here. Such as UV Ceti, which is actually a pair of red dwarfs 9 light years away, and Mira (omicron Ceti) - perhaps the most famous variable. See below for these stars.


Double stars:

Gamma Ceti (Struve 299) is perhaps the finest binary in Cetus. Some observers find a colour contrast, yellow and blue: 3.5, 7.3; PA 294, separation 2.8".

Nu Ceti: 5.0, 9.5; PA 83, separation 8".

Struve 186 is a close binary of two equal stars, with an orbit of 170 years: 7.0, 7.0; currently PA 60 and separation 1.1".

beta 395 is a very rapid visual binary, with orbit of 25 years: 6.3, 6.4; presently PA 289 and separation 0.5".

For a selection of binocular and telescopic binaries, see the Binocular link below.


Variable stars:

Omicron Ceti, better known as Mira, "The Wonderful". This is the prototype of long period variables and one of the earliest variables ever discovered.

A Dutch astronomer, David Fabricus, considered it a nova in 1596. It wasn't remarked on again until 1603, when Bayer put it in his catalogue under the name omicron. He apparently had stumbled across the star at one of its maximums. Later attempts to find the star failed, until once again it made an appearance. Since mid-seventeenth century the star has been studied closely.

The star has a potential range from as dim as 10 to as bright as 2.0, although it usually reaches a maximum visual magnitude of from 3 to 4. The average period is 331.96 days and the star only maintains its maximum for a few weeks, before rapidly losing its brilliance.

In the year 2000 the maximum should occur in September. But the period may change slightly. It has been known to vary from as long as 353 days to as short as 304 days. Burnham (p. 636) has a finder's chart.

UV Ceti is the prototype of a classification of variables known as flare stars. UV Ceti is actually component B of a binary system composed of two red dwarfs, both having a visual magnitude of only 15.5. Combined, their magnitude is about 12.

Every ten hours or so UV Ceti suddenly jumps in magnitude. In just a few seconds it will increase by three or four magnitudes, even five magnitudes on occasion. Then over the next five to ten minutes the star settles back down to its former dim self.

Being so faint, flare stars must be very close to the solar system to be noticed; indeed many of them are within fifteen light years from us. UV Ceti is 8.4 light years away. (The closest flare star is V645 Centauri, better known as Proxima, or alphaC Centauri, which is 4.22 light years away.)

The two stars which make up this binary are among the least massive stars known, with each component having about a tenth of the sun's mass.

The binary's period is about 26 years and the separation remains roughly 2".

To find UV Ceti first locate tau Ceti, then the binary h 2067 (see above). UV Ceti is in the same viewing area, just half a degree to the southwest of h 2067. Burnham (p. 642) has a finder's chart.


Deep Sky Objects:

M77 (NGC 1068) is a small spiral galaxy seen face on, one of the so-called Seyfert gallaxies, which means it has a radio source - a feeble example of a quasar.

M77 is about 50 million light years away, and is found one degree SE of delta Ceti.

NGC 247 is a large and fairly bright spiral galaxy with compact nucleus.


For a closer appreciation of Cetus, visit the Binocular Section.


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Richard Dibon-Smith.