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Royal Astronomical Society of New Zealand

Cetus, a constellation for November

Contributed by Paul Rodmell, Southland Astronomical Society

CETUS "The Sea Monster" (Pronounced SEE-tes).

Chart showing the constellation.

This is an ancient constellation depicting a sea monster that threatened to devour Andromeda, before Perseus rescued her.  Cetus is found in the sky basking on the shores of the constellation Eridanus, the River, and near Aquarius the Water Carrier.  The constellation is large but faint and lies in a rather barren part of the sky.

Cetus contains some interesting stars, particularly ο Ceti and τ Ceti.  UV Ceti, is a faint but famous prototype of a class of erratic variable variables known as flare stars.  These are red dwarfs that undergo sudden increases in light output lasting a few minutes.  The outbursts of the flare star component of UV Ceti take it from its normal 13th magnitude to as bright as 7th magnitude.

To find Cetus, look north between the Great Square of Pegasus and Aldebaran, about half way up from the horizon.

Chart showing Cetus - as seen about 10.30 pm (NZDT) mid November.

The horizon is for the south of the South Island of New Zealand

Cetus chart

Constellation Aquarius Constellation Sculptor Constellation Fornax Constellation Lepus Constellation Auriga Constellation Perseus Constellation Triangulum Constellation Aries Constellation Eridanus Constellation Orion Constellation Taurus Constellation Pisces Constellation Pegasus Constellation Andromeda

Some stars and interesting objects in the Constellation

α Ceti (Menkar, meaning nose) is a magnitude 2.5 red giant star 220 light years away. Binoculars show an unrelated magnitude 5.6 blue companion, lying over six times further away.

β Cet (Deneb kaitos, tail of the whale) is a magnitude 2.0 yellow giant star, the brightest in the constellation. It lies is a magnitude 96 light years away.

γ Cet (Kaffaljidhmah), is a beautiful close double star of magnitudes 3.7 and 6.4, with colours of white and yellow. The system lies 82 light years away.

ο Cet (Mira, the wonderful).  Mira is a long known red variable star recognised by the Dutch astronomer David Fabricius in 1596.  It varies in brightness between about 3rd and 9th magnitude with a period between 320 and 370 days, with a mean of 331 days as it swells and contracts.  At maximum the diameter is slightly more than 200 times that of the Sun, or roughly the diameter of Earth's orbit.  At maximum it is an unaided eye object, and at minimum at least good binoculars are needed to see the star.

τ Cet is one of the closer stars to the Sun, that is similar to the Sun. It is a yellow dwarf lying 11.9 light years away appearing at magnitude 3.5.

M 77 (NGC 1068) is a small softly glowing 9th magnitude face-on spiral galaxy appearing near δ Ceti. Merchain discovered this galaxy in 1780. It is classified as a Seyfert galaxy, a type of spiral galaxy with a bright nucleus. Seyfert galaxies show rapidly expanding gas in the central region. M77 lies about 50 million light years away.

Visibility

Cetus straddles the celestial equator with its tail extending into the southern hemisphere. It is highest in New Zealand skies at about 11:00 pm (NZDT) in mid November, an hour later at the beginning of the month and an hour earlier by the month's end.

It remains visible in the evening sky until about the end of February, by which date the constellation will be low and to the west as evening twilight darkens. Shortly before it sets, Cetus is in the west sprawled along the horizon across over 45° of sky.


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