The Night Sky in November, 2016

Transcription

1 The Night Sky in November, 2016 Recently, I gave my Myths and Legends of the Stars talk to a U3A group in Newbury. One of my friends commented that she would love to hear this talk. So, this month I have decided to do something different. If you know some of the Greek legends about the stars, then this can help you read the night sky. I am going to illustrate this with the legend about Perseus. Firstly, you need to find the constellation of Cassiopeia. All the stars in this constellation are very bright and so you should have no problem finding it on a clear November night. The star chart below shows you how to find it. Look in the North and find the Plough which is on the right of the star chart below. Find the stars Merak and Dubhe which you can see at the top of the bowl of the Plough. Follow the line of these stars until you reach Polaris this will be the first bright star you encounter. Polaris is also known as the Pole Star since it is situated near the North pole. It is the brightest star in that region but note that it is not as bright as many people expect it to be. Carry on the line beyond Polaris and you will come to the constellations of Cassiopeia and Cepheus as shown in the left of the star chart below. All these constellations close to Polaris are circumpolar. This means that they are in the sky all night and all the year round. Since we are spinning on our axis around the pole, these circumpolar constellations seem to us to be rotating around Polaris. So, sometimes Cassiopeia will look like a W and sometimes it will look like an M. But it will always be on the opposite side of Polaris to the Plough and will always have Cepheus to the right of it. The star chart below shows the sky high in the South at 22:00 GMT on November 15 th. In the middle of this chart, you can see the distinctive W shape of the constellation of Cassiopeia. To the right of Cassiopeia, you can see the constellation of Cepheus which looks like the gable end of a house. According to Greek legend, Cepheus was the King of Ethiopia and Cassiopeia was his Queen. They had a beautiful daughter called Andromeda. In the star chart below you can see the constellation of Andromeda beneath and to the left of her parents. Andromeda consists of two lines of stars forming a wedge shape going upwards from the bottom centre of the chart. On the right of it is the Andromeda Galaxy, M31. On clear November nights, you can just see this with the naked eye even though it is 2.5 million light years away and a light year is 6,000,000,000,000 (6 trillion) miles!

2 Queen Cassiopeia boasted about the beauty of her daughter and claimed she was more beautiful even than the Nereids, the daughters of Neptune the sea god. This infuriated Neptune who demanded that Cassiopeia should be chained to a rock and sacrificed to the sea monster. In the image below, you can see Andromeda chained to the rock. This is one of the cards of a boxed set of 32 cards called Urania s mirror. Urania is the Muse of Astronomy. The cards were produced by the Reverend Richard Rouse Bloxham of Rugby in For each constellation, he perforated a card with holes showing the positions of the brightest stars. Then he painted an image in water colours of the Greek legend associated with that constellation. If you hold the card up to the light, you can see the main stars shining through the card. I always think this is a nice project for children to do and learn something about the stars in the process.

3 The image below shows the hero Perseus. He was on his way home having killed the Gorgon Medusa. He was carrying the head of Medusa home to prove that he had indeed killed the Gorgon. You can see him carrying the head in the card below. You may remember that if you looked into the eyes of Medusa you would be turned to stone. But Perseus was helped by the gods. Minerva gave him a polished shield to use as a mirror, Mercury gave him winged feet and Pluto gave him a helmet which made him invisible. With this help, Perseus slayed the Gorgon. On his way home, he came across a beautiful maiden chained to a rock. This was Andromeda about to be sacrificed to the sea monster. When the monster arrived, Perseus held up the head of Medusa (which apparently still worked even though it had been chopped off) and turned the monster to stone! Perseus fell in love with Andromeda of course! They married and ruled happily together over the Argolid! If you look back at the second star chart above, you can see the constellation of Perseus to the left of Cassiopeia and above Andromeda. I always think that Perseus looks like a chicken s wishbone. If you look down the right-hand bone you will see a famous star called Algol. This is famous because it is a rotating binary star - that is it consists of two stars which rotate around each other. When the smaller star passes in front of the larger star it dims it. Algol changes in magnitude every days. So, if you keep an eye on it over a period of a few days, you should see its brightness change by comparing it with other stars nearby. Algol is also at the head of a pattern of stars called Caput Medusa which represents the head of the Gorgon. You can see the position of the head on the card above. Now you can see that there is a family grouping of constellations in the second star chart above. That is - Cassiopeia, Cepheus, Perseus and Andromeda are related to each other by the Greek legend. Since the positions of stars do not change very much with respect to each other, then these constellations will always be together when they are in the night sky. See if you can identify them all this November. What else is there to look out for this month? At the beginning of the month, the Sun will set at 16:36. About 30 minutes later Venus and Saturn will be visible low on the south-western horizon. They will be joined by a young Moon. Mars will also be nearby in the south.

4 The Leonid meteor shower occurs this month and will peak on the night of November 16 th /17 th. Unfortunately, a nearly full Moon will spoil the view this year. If you want to see them, look in the opposite direction to the Moon. If you are an early riser, then look in the south-east just before dawn towards the end of the month and you will be treated to the sight of Jupiter very close to a thin crescent Moon. The star chart below shows the sky at 6am on November 25 th. Uranus and Neptune are still very favourable planets to see this month. The star chart below shows the sky high in the south at 22:00 on November 1 st. You can see that Uranus is in the constellation of Pisces the Fish. The circlet, which is the head of the fish, is just below the Great Square of Pegasus. Neptune can be seen lower down and to the right in the constellation of Aquarius. You will need binoculars or a small telescope to find these planets. Some of my astronomer colleagues claim that they can see four of the moons of Uranus and also Neptune s largest moon Triton in a small telescope. Worth trying if you have access to a scope. Now to the Southern hemisphere!

5 What's Up in the Southern Hemisphere? Unfortunately, you can t see Polaris or the constellations that are circumpolar in the northern hemisphere. However, you can see the constellations of Perseus and Andromeda so some of the Greek legend is meaningful to you. The star chart below shows the sky in the North over Sydney at 22:00 on November 30 th You can see Perseus in the bottom right of this chart. It looks like a chicken wishbone but is upside down compared with what we see. You can see the variable binary star, Algol in the left-hand bone. To the left of it you can see the whole of the Andromeda constellation with the Andromeda Galaxy below it. To the left of that is the Great Square of Pegasus and above it you can see the circlet of Pisces the Fish. To the right of this is Uranus and, to the left of the chart, you can see Neptune in the constellation of Aquarius. You also have the good fortune to have a better view of Mars than we do. The star chart below shows the sky in the west at 22:00 on November 1 st. You can see Mars high up in the magnificent constellation of Sagittarius. To the left and below this is half of the constellation of Scorpius and very close to the horizon you can see the planets Venus and Saturn.

6 The star chart below shows the constellations that are circumpolar for you. There is no star like Polaris which is close to the south pole but I have marked its position with a red cross. I have also shown the Milky Way highlighted in blue. You can see that the constellation that contains the south pole is called Octans named after the octant instrument. The constellations around the pole (starting at the bottom and going round clockwise) are Apus (the Bird of Paradise with no feet), Chamaeleon (the Chameleon), Volans (the Flying Fish), Mensa (Table Mountain in South Africa), Hydrus (the Water Snake), Tucana (the Toucan) and Pavo (the Peacock). Note the two small patches of the Milky Way coloured blue. The large one in the constellation of Dorado (the Goldfish) is the Large Magellanic Cloud (the LMC). The small one in the constellation of Tucana is the Small Magellanic Cloud (the SMC). These are named after the sailor Ferdinand Magellan who used them as navigational aids. They are a magnificent sight in the southern hemisphere and do look like clouds as can be seen in the image on the left below. They are in fact two irregularly shaped dwarf galaxies which are slowly being absorbed into the Milky Way. The LMC is 160,000 light years away and the SMC is 200,000 light years away. The small object to the left of the SMC is a globular cluster of stars called 47-Tucanae. This is shown in the image on the right below taken by the Hubble telescope. Well that is all until next month. Meanwhile happy stargazing! Dark skies! Valerie Calderbank FRAS