I have already written about the night sky in Summer and promised that I would do it later for the sky in Autumn and Winter - even though not too many people come to Provence in Winter. Sadly from the stargazing point of view as you don’t have to stay up so late to see the stars - and we often get lovely clear skies. As with what I wrote about the summer sky, it’s really written for children, but adults may find the odd thing of interest!
I’m starting in November, which is really more like Autumn than Winter. In November, you can already see the great square of Pegasus and the adjacent constellation of Andromeda, both of which are worth looking for.
Pegasus
First, Pegasus. Although it gets its name from a horse - and a horse with wings at that - it is in fact a big square, pretty easy to pick out. The main stars are the four corners.
The interesting thing about it is that there are very few stars within the square. Why ever? The reason is that it operates like a window and we are, in a sense, looking through the
window out of the Milky Way.
The Milky Way is a spiral galaxy, like a catherine wheel, and we in our solar system are on one of the limbs. When we look up at the milky way in the sky, we are looking towards the centre of the galaxy with all its hundreds of billions of stars. Looking through the window of Pegasus, we are looking the other way - out of the galaxy. We are looking out into deep space. Astronomers with modern telescopes can identify other galaxies. Unfortunately, we can’t do that.
Constellations
This is the point where we should look at some of the constellations.
As I’ve mentioned, Pegasus is right up there - named after a horse with wings. The big square is apparently its body. I’m not at all sure where its wings are meant to be.
Top left from the sqare is the constellation of Andromeda. The shape of the constellation is a thin V, upside down, ending at the top left corner of Pegasus. This is easier to imagine in terms of its name - easier than the horse! You can imagine that it represents Andromeda, a beautiful girl, falling down towards the horse. I’ll come back to the famous Greek legend that it’s based on. And there’s also another reason for looking out for Andromeda, the constellation, which we’ll also come on to.
Looking overhead, more towards the north, is Cassiopeia. It’s quite easy to spot as it’s in the shape of an M - rather a flattened out M. Actually, it’s always visible, winter and summer, because it appears quite near the Pole Star. The Pole Star is always due north with all the other stars moving around it as the year goes by. So, in Summer you can still see Cassiopeia. Although then it’s the other way up - it’s then a W, also flattened out.
Greek Myths
We have to understand the ancient myths to try and see what our remote ancestors were
getting at.
Cassiopeia had a very beautiful daughter called Andromeda and annoyed some of the gods by boasting about how beautiful she was - probably a mistake then, as it would be now. Poseidon, one of the gods, got a sea monster to cause endless devastation on Cassiopeia’s country (Ethiopia, since you ask). Her husband decided to sacrifice Andromeda to placate the sea monster. She was therefore tied up on a rock by the sea for the sea monster to attack her. But Perseus came to the rescue - on his horse Pegasus! They fell in love and lived happily ever after.
So, we have constellations for Cassiopeia, Andromeda and Pegasus - as well as constellations, not far off, for Perseus and the sea monster. The story is one of the more famous of the Greek myths, which were much better known way back that they are now. In particular, the story of Andromeda being tied naked to a rock, with a sea monster lurking in the background, excited the imaginations of many nineteenth century painters, so that versions of it can be found in various art galleries around the world.
Who decides about the constellations?
Looking up at the constellations of Pegasus and Andromeda, you see a curiosity. Andromeda’s head and one of the corners of Pegasus are the same star, Alpheratz. The name means the navel of the horse, so you’d have thought it should be part of Pegasus. But actually, now it has been shifted. Now it is in Andromeda and Pegasus has lost his navel. Who decides these things?
Originally we get the names of all the well-known constellations - certainly all the ones we’ve been looking at - from the Greek polymath Claudius Ptolemy, who lived during the 1st century AD in Alexandria, then part of the Roman Empire. He didn’t make the names up, but he assembled all the information in a book that still survives. He has the star Alpheratz in both constellations.
When astronomers got together at the beginning of the 20th century, they obviously thought that this wouldn’t do. A body called the International Astronomical Union (IAU) had been formed to decide where all the constellations begin and end. There are now 88 constellations, although Ptolemy only had about half that number - partly of course because he didn’t know about those seen from the southern hemisphere. And one of the things the IAU decided was that Pegasus should lose his navel rather than Andromeda losing her head. Probably a sensible decision.
The Andromeda Galaxy
Now to one of the most fascinating things about the Andromeda constellation.
Not that easy to see. You have to follow up the right hand part of the V of Andromeda, consisting of three stars. When you get to the second of the three stars, you look to the right. At the point that is about the same distance as each of the Andromeda stars is to its neighbour is the Andromeda Galaxy.
It is only a blur - and only visible with some difficulty on a very clear night. It is, of course, another galaxy, quite similar to the Milky Way as it is also a spiral galaxy. But it’s much bigger. It’s one of the largest galaxies we know of, about half as big again as ours. And its about the only thing we can see with the naked eye (if you’re lucky) outside the Milky Way.
It’s not difficult to understand why it’s difficult to see. It’s over 2 million light years away - meaning that the light we can (just) see started coming to us over 2 million years ago, when there were as yet no human beings on Earth, just the apes from which we are descended.
The Andromeda Galaxy consists of hundreds of billions of stars, as does the Milky Way. It’s hard to believe that somewhere out there there isn’t a solar system with forms of life, possibly including intelligent beings, who are busy looking through their telescopes at us - and wondering who we might be.
My next instalment will be in Winter proper - when we’ll be able to see Orion and his belt. As well as the strangely named Betelgeuse, which we should try to avoid calling “beetle juice”.
Tony Herbert
5 November 2023
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