Probably the most famous galaxy in the entire night sky is well on show this month high overhead in mid-evening. It is of course, the Andromeda Galaxy! It’s the furthest object that is possible to see with just the naked eye at over 2.5 million light years and is arguably one of the most beautiful such object in the heavens too.
It is surprisingly large; the diameter of the Full Moon would fit inside it over 3 times! The reason you can’t see it easily, is because it is quite faint. Binoculars will help here. 7×50 or 10×50 are by far the best instruments to enable you to see this astounding object with your own eyes. But how do you find it?
First, you need to find the ‘Square of Pegasus’. The four stars which make up the ‘square’ are quite easy to spot on an Autumn evening. Using the top left hand or more correctly, most north-eastern star in the square, named Alpheratz, move to the next brightest star to the east. This is delta Andromedae. Once again, move in an easterly and now slightly northerly direction to find the next bright star in the chain. This is Mirach. Here you veer off at 90° heading north and slightly west. The next brightest star which you’ll come to is mu Andromedae. One more hop in the same direction and along the same line and for the same distance you moved from Mirach to mu, will take you to the Galaxy. It is unlikely that you’ll see any structure with the naked eye or even binoculars, but what you will see is the glow of the core of the galaxy surrounded by a fainter glow from the spiral arms. A medium to large telescope will start to resolve some structure, but normally the field of view is restricted, so you will have to move around with your scope to take in the whole object.
Here then, is a method to find the Andromeda Galaxy, but what are you looking at? A galaxy is an island universe of stars in space. The number of stars in this Galaxy are estimated to be around 1 trillion. It is also thought that there is a super-massive black hole in the centre of the Galaxy, although this is thought to be the case in many such galaxies, including our own ‘Milky Way’ galaxy. Messier 31, as the Andromeda Galaxy is otherwise known, is part of the ‘local group’ of galaxies. I hope you enjoy looking at our neighbour!
One of the other objects of note well on display in this region too, is the Perseus Double Cluster, labelled NGC 884 and NGC 869. Again, this is a wonderful object for those armed with binoculars or a small telescope. The constellation of Perseus looks a bit like an upside-down letter ‘Y’, with the stem pointing towards the constellation of Cassiopeia. If you draw an imaginary line along from the end of Perseus marked by the star eta Perseii, towards Cassiopeia and travel along it about one third of the distance, you’ll come across the Double Cluster. This pair of open star clusters are breathtakingly beautiful and well worth lingering on, looking like diamonds scattered on to black velvet. I urge you to go and view them.
While you are in Perseus, take a look at the star beta Perseii or Algol. This is a variable star. This means the brightness of the star varies. It is one of countless such objects in the night sky, but this one is fun to watch, because it is quite bright and easy to find and varies noticeably over a period of just a few days and regularly, so it’s easy to follow. It is an eclipsing binary star, that is it consists of two stars which orbit around their common centre of gravity and when the smaller star is eclipsed by the larger, the brightness of the combined object dips. When the smaller star passes in front of the larger, the light drop is less marked, but visible nonetheless. The light dips last for a few hours and occurs every 2 days, 20 hours and 49 minutes. If you have never studied a variable star before, Algol is a great one to start with.
Not far from Algol, is the open star cluster M34. You can find it approximately half way between Algol and the star Almaak or gamma Andromedae. It is nowhere near as spectacular as the Perseus Double Cluster, but it is still quite a pleasing object to observe. It is thought to lay at a distance of 1,500 light years from us. Finally, laying about half way between M34 and the star Almaak is a faint galaxy known as NGC 891. This is an edge on spiral galaxy and may even be similar to our own Milky Way. It’s a challenging object to see although it shouldn’t be too difficult in a telescope of at least 8-inches or 200mm in diameter.
There are plenty of other clusters, nebulae and galaxies in this region and it is worth spending some time with a chart and binoculars or a telescope, picking you way through these wonderful objects. Happy hunti