Queen Cassiopeia rules the Autumn night skies - Martin Lunn looks at the stars for October

In October Queen Cassiopeia rules the night sky, the famous letter ‘W’ shape that forms the constellation being as high as it can become during the year. This spectacular constellation which sits in the middle of the Milky Way can be seen throughout the year, but if you want to see Cassiopeia at its best, now is the time to look for it. Of course, with Cassiopeia so high in the sky, the familiar shape of the Plough is now at its lowest point in the north, although still well above the horizon. These two groups of stars are the most distinctive of what astronomers call ‘circumpolar constellations’: groups of stars that, as seen from Britain, never set.

The Summer Triangle of stars Altair, Deneb and Vega can still be seen and is to be found to the south west, but as we approach the end of the month it will be much lower in the sky. Of the large but faint and obscure summer constellations that occupied so much of the southern sky, Hercules, Ophiuchus and Serpens are all slipping away in the south west.

October is the month when the autumn constellations are at their best, but the sky never stops changing and if we look to the north east we see the winter constellations beginning to appear. The Pleiades or Seven Sisters become noticeable, and in the north east is the bright star Capella in the constellation of Auriga the Charioteer that will occupy the overhead position during winter.

I have already mentioned Cassiopeia which is a spectacular sight, and once you have identified that familiar ‘W’ shape you will easily find it in the future. The middle star of the ‘W’ is Gamma Cassiopeia; it has no formal name. This star is what astronomers refer to as a ‘variable star’. A variable star is a star that changes in brightness either over a regular or irregular period of time. This can be due to a variety of reasons. Normally Gamma Cassiopeia is about as bright as the North Star but periodically it can become much brighter and also much fainter, so it is always worth taking a look at.

When talking about names I should explain that the 24 brightest stars of each constellation have a letter of the Greek alphabet issued to them. (The Greek alphabet consists of 24 letters.) The brightest star is labelled as alpha, the next brightest beta, the next gamma and so on, ending with omega. This system of designating the stars was introduced by the German astronomer Johann Bayer in 1603.

In mythology Cassiopeia was the boastful queen who annoyed Neptune, god of the sea, who then sent a monster called the Kraken to attack her land. The only way to save her land was to take her daughter Andromeda, chain her to a rock and let the monster eat her! With Andromeda chained to a rock the monster appeared and everything seemed lost, but at the last minute our hero Perseus, riding the winged horse Pegasus, arrived on the scene. Perseus has just killed Medusa, a creature whose hair was made of snakes, and whose appearance was so horrible that if you looked at it you would turn to stone. By good fortune Perseus still had the head of the Medusa with him and when he pointed it towards the monster, it promptly turned to stone. Perseus landed, rescued Andromeda and they were married and lived happily ever after. All these characters can be found in the night sky, although today the Kraken has turned into the constellation of Cetus, a much less harmful whale.

If you look below Cassiopeia you will be able to see the four stars that form the Square of Pegasus. It is very conspicuous but because the square is so large it does not at first stand out. The square provides a good opportunity to show how un-crowded the sky can be. Try counting the number of stars that can be seen with your naked eye inside the square and you might be surprised by how few are visible.

Linked with Pegasus is Andromeda which is seen as a line of stars moving away from the top left hand star of the square of Pegasus. For reasons I cannot explain this star has been given a free transfer to the constellation of Andromeda making this star alpha Andromeda!

What really attracts the attention to Andromeda is one object of great interest; the Andromeda Galaxy. To find the Andromeda Galaxy, start with alpha (the top left star of the Square of Pegasus), move to the left along the line of stars, go past delta and stop when you arrive at the next star, beta, and at this point you need to look upwards and slightly across to two faint stars Mu and Nu. The Andromeda Galaxy is just to the right of Nu. It is visible to the naked eye on a really clear night if you know exactly where to look. If you can find the galaxy you will be looking at the most distant object that you can see with your eye without binoculars or telescopes. The Andromeda Galaxy is 2.2 million light years away.

If we go back to the square of Pegasus and use the two right hand stars to draw a line down towards the horizon, we see the most southerly of the bright stars visible from Britain. This is Fomalhaut, in the constellation of Piscis Austrinus, the Southern Fish. With Fomalhaut being so low in the sky the period of time to observe it is quite short so if you want to see it, you had best look for it this month.

Most of the other constellations in the south during autumn are large but faint. In the summer we had Hercules, Ophiuchus and Serpens which have now been replaced by equally large, dim groups, including Aquarius the Water Bearer, Capricornus the Sea Goat and Cetus the Whale. However, before I finish my look at the October sky I cannot resist mentioning one more constellation, Triangulum the Triangle, which can be found just below the line of stars that make up Andromeda. Triangulum is not bright but it is one of the few groups that actually looks like the object it is supposed to represent.

The Planets in October

We stick with the theme of seeing the planets in the morning sky just as we did last month; the difference is that while in September, Mercury and Mars were close together, this month it is Mars and Venus. On the mornings of October 5 and 6, Mars and Venus will almost be touching each other in the morning sky at around 6 am, just before the Sun rises. Venus is much the brighter and will appear as a bright white looking ‘star’ while Mars will look much fainter, appearing as a red ‘star’.

Of the other planets, Mercury and Jupiter are too close to the Sun, while Saturn might just be seen low in the south west in the evening sky before sunset.

Meteor Showers

The Orionid meteor shower will peak on the night of October 20/21. It is not the most spectacular meteor shower of the year, with possibly around 15 meteors per hour being seen, but the Orionids are the remains of one of the most famous of all comets, namely Halley’s Comet, so they are worth having a look for.

Phases of the Moon for October

Full Moon 5, Last Quarter 12, New Moon 19, First Quarter 27.

This month’s full moon is called the Hunter’s Moon, because following on from last month’s Harvest Moon when people harvested crops; October was the time for hunting animals using moonlight to help find them, with the meat being stored for the coming long winter nights.

British Summer Time Ends

On Sunday, October 29 British Summer Time, or BST, ends and the clocks will go back one hour. Although not popular with everyone it does allow astronomers more time to observe the night sky.

The next meeting of the Earby Astronomical Society will be on Friday September 29 at All Saints’ Church, Earby from 7.30pm-9pm. The speaker will be Martin Lunn MBE FRAS, Earby Astronomical Society, and the title of the talk will be ‘Cosmic Catastrophes, The Threat from Space ’.

Everyone welcome.