The Constellations

Sam has always loved astronomy and the Night Sky, and helped with the Astronomy Club at his Junior School. When he left the teachers and parents gave him his own astronomical telescope as their way of saying “thank you” to him for all his work with the Astronomy Club.

He uses it a lot. He has not yet made any new discoveries but he lives in hope: many comets are first detected by amateur astronomers and named after them (these days most professional astronomers are looking for things far further away from the Earth and the Sun than comets) so perhaps one day there will be Sam’s Comet! But owning his own telescope does not stop him from looking at and telling all his friends about what you can see in the Night Sky without one - after all the telescope was not invented until 1608 so for at least six thousand years before that astronomers had had to manage without, and did so very well indeed. Even the great Nicolaus Copernicus (1473 - 1543) did not have a telescope!

Often on a fine evening Sam and his friends sit outside and watch the sun set and the stars come out. They sometimes play a game, particularly if there is someone in the group who has not played it before.

They watch the Sun set, and then wait for the first “star” to appear - this could be a fixed star or a planet (these terms are explained later) but in this game it does not matter which. They might have to wait several minutes. The first person to see one shouts “star” and points to it. They all count the number of stars they can see, here it is just one, and then count them again, and then wait for the next one. Each time someone sees a new star they all count the number of stars they can see, and then count them again. This is easy - up to seven! After seven they find that in the time it takes them to count the stars another one has appeared! On a clear night by the time the sky is fully dark Sam and his friends can see more than four thousand stars, far too many to count. Sam is very sad that today so many children live in towns and never see the Night Sky in all its glory because of all the street lights.

This Game is best played at the end of August, on an evening when there is no Moon in the sky. During the middle of the summer the sky is not really dark enough to see all the stars until well past Sam’s bedtime, and after the end of August the evenings are getting a little cold for sitting out of doors for a long time.

Sam and his friends like watching the way the planets move across the sky against the background of the fixed stars, but with only five planets to look at but more than four thousand stars this is not easy! One day when it is too wet to do any real star-watching Sam uses his iPad to explain how it is done.

He shows them a (made-up) map of a part of the sky showing twenty stars and one planet.

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He then shows them the same part of the sky as it appears a few weeks later.

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He asks them to explain how the planet has moved against the background of the stars.

They all have different ideas, but none of them work. Then he says ” Dont’t look at the stars, look only at the patterns they make” and suddenly it is easy.

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The stars have kept the same positions but they have rotated, the Trapezium has moved into sight and the Parallelogram has moved out of sight, and the planet has moved from the Square to the Kite!

The Ancient Astronomers did exactly the same: they looked for the patterns the stars made: these patterns are called constellations. Orion, Pegasus, Aries, Scorpio, Cancer, Leo, Ursa Major, Gemini, Andromeda are all constellations. Originally astronomers from different parts of the World used different patterns, but all today’s astronomers use the patterns the Roman astronomers used, two thousand years ago, but making up some more names for the constellations visible only from the Southern Hemisphere which the Romans could never have seen. Here are some of the constellations - only the brightest stars are shown.

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The ecliptic and celestial equator are explained on other Pages. Where they meet is called The First Point of Aries and it has its own special symbol. It moves slowly: it was in Aries when it was named but it is now in Pisces.

Sam does not think that Aries looks much like a ram but this does not prevent him from finding it in the sky.

The Plough (in America Dipper) is not actually a constellation, although many books say that it is, it is only a part of the constellation Ursa Major (The Great Bear - but a bear with a tail!).

We can only see the stars and constellations between Sunrise and Sunset, and this means that as the Earth moves round the Sun we shall see different constellations at different times of the year.

When Sam first became interested in astronomy he was given a book which gave a map of the Night Sky for each month of the year - constellations and stars only, not the planets, because the planets move through the constellations: Mars might be in Aries today but it then moves into Taurus, then Gemini, then Cancer and so on - this is described on another Page.

Today he does not often use this book, he usually uses an App (Planets) on his iPad. He holds his iPad up to the sky and it shows everything, Moon, stars and planets, even comets, he can see.

Although only a very few of the very brightest stars (Sirius, Canopus, Betelgeuse, Arcturus, Viga, Aldebaran, etc) have ever been given names, today’s astronomers have catalogued every known star (millions and millions of them) in our galaxy: the catalogue entry includes the name of the constellation it is in and a combination of Greek letters and numbers. Sam finds explaining this to his friends boring - you do not need all this for naked-eye astronomy. Many star names are Greek or Roman, but lots more are Arabic.

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© Barry Gray April 2020