Cetus the Whale is a sprawling autumn constellation south of Pisces.
Here it nudges into the band of sky described as the Zodiac and consequently the Moon and planets can find themselves inside Cetus from time to time.
The outline resembles a whale with a head to the east and raised tail northwest.
The stars tell a different story though, the Whale’s tail being represented by a misshapen pentagon that contains Menkar (Alpha (α) Ceti), the name meaning ‘nostril’.
So the apparent tail is actually the head!
Cetus is also home to pulsating variable star Mira
The base of the pentagon is Kaffaljidhma (Gamma (γ) Ceti) a shortened version of ‘Al Kaff al Jidhmah’, derived from the Arabic meaning ‘the cut-short hand’.
This name originally referred to a group of five stars in Cetus; Gamma, Xi1 (ξ1), Xi2 (ξ2), Delta (δ) and Mu (μ) Ceti.
The Chinese Tiān Qūn refers to the asterism formed from Alpha, Kappa (κ), Lambda (λ), Mu, Xi1, Xi2, Nu (ν), Delta, 75, 70, 63 and 66 Ceti.
Tiān Qūn translates to ‘circular celestial granary’, with Gamma Ceti known as ‘the eighth star of circular celestial granary’.
Kaffaljidhma is a triple system. Through the eyepiece Kaffaljidhma A and B are easily resolved as a double, A being a mag. +3.6 A3 type star, B a mag. +6.3 cooler F3 type.
Through a telescope this white-yellow pair are separated by 2.8 arcseconds and often look blue-yellow due to colour contrast.
Mag. +10.1 Kaffaljidhma C is an orange star of type K5 and sits 0.25˚ from A and B.
While A and B have a 320-year orbital period, C takes around 1.5 million years to orbit the other two.
The system is 82 lightyears away, Kaffaljidhma A being around twice as massive as the Sun.
