The December skies are starting to get brighter compared with those of autumn. We still have the autumn stars over to the west, and the Square of Pegasus still makes a great signpost, but over to the west are signs of things to come, as the Milky Way comes onto the scene again.
You can find the Square of Pegasus about halfway up the sky, and it’s bigger than a lot of people expect. It’s not a perfect square either but let’s not quibble. Find out more about Pegasus, Pisces, Cetus and Andromeda in our November page including information on viewing the famous Andromeda Galaxy.
One feature of the rather faint constellation of Cetus which you might notice is the gap in its line of stars which is labelled Mira. The map shows the situation for most of the time, but sometimes you will actually see a star at that spot, of about the same brightness as the other stars in Cetus or maybe even brighter. The star Omicron Ceti varies in brightness by a factor of 250 or more. More often than not it’s too faint to be seen with the naked eye. For example, in 2017–2018 it spent 224 days below mag 5.7, and only 117 days above that brightness. It was the first variable star to be recognised, which was in 1596, and its behaviour led to its becoming referred to as Mira, meaning ‘Wonderful One’.
Cetus, the Sea Monster, also plays a part in a mythological story which is played out nightly in this part of the sky. Our distant ancestors, who of course lacked even access to writing and books, used the stars as a storybord, and one of the most famous tales they told concerns the vain Queen Cassiopeia, whose W-shape of stars is just above our chart for this month, and is practically overhead at this time of the year, along with King Cepheus, her husband. Cassie was a notoriously vain queen who was fond of talking about how beautiful she was. Maybe you know people like her. Her boasts so annoyed Poseidon, king of the seas, that he placed her in the heavens in such a spot that she often has to grip hold of her throne to avoid falling off. As a further punishment, her daughter Andromeda was chained to the rocks on the coast, where she was in danger from Cetus. But along came the hero Perseus, at the top of our map, and rescued her.
Also visible now are the beautiful Pleiades, or Seven Sisters, which you can see in even city skies at this time of year. People with reasonable eyesight can count at least seven of these stars, and indeed there are nine of them with names. The answer to this conundrum is that they are there with their two parents, making a nice celestial family group. So take a look at them with binoculars if you can, or with a small telescope at its lowest magnification. Their name is pronounced ‘Ply-adeez’. And another star cluster, larger in the sky, is the Hyades (yes, you guessed it, pronounced ‘Hy-adeez’), over to the left in Taurus.
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