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Getting started in astronomy
BY KEITH COOPER
ASTRONOMY NOW

Posted: 9 January 2013


Getting Started in Astronomy
Members of HantsAstro is Hampshire embark on a Moonwatch. If you live in Hampshire and would like to join a society, take a look at HantsAstro's website at www.hantsastro.org. Image: Graham Greene.

Let's dispel one myth and reassure everyone who is new to astronomy from the beginning: you do not need a telescope to do astronomy! There are many sights visible in the night sky for you to see just by going out into your garden and looking up; many more, in fact, than you may have possibly imagined.

Yes a telescope, or a pair of binoculars, is a useful asset, but for beginners new to the delights of the heavens they are not immediately essential (although you will want to quickly progress on to them). But we're talking about starting points here, and the good ol' human eyeball shouldn't be underestimated.

The stars are an obvious place to begin. They might appear randomly dotted across the sky, and so they are, but to the ancient Greeks they appeared in patterns, constellations, depicting great heros and beasts from their mythology. So we have Orion the Hunter, Perseus the Hero, Pegasus the Winged Horse, Ursa Major the Great Bear, Auriga the Charioteer and 83 other constellations in total. Not all of them are visible from the UK, and those that are are not always visible all year long. So we'll focus on those constellations that can be seen during the winter, should you step outside under the night sky this evening.

Constellations
There are perhaps three constellations that immediately stand out thanks to their distinctive shapes of bright stars: Ursa Major, Cassiopeia and Orion. Let's start with the Great Bear high up in the north-east; casual observers may be more familiar with this constellation in its guise as the 'Plough'. The Plough is what we call an asterism; an unofficial constellation within a constellation. Ursa Major extends beyond the saucepan-shaped pattern of stars that is the Plough, but it is the Plough that is most noticeable.

The Plough
The Plough asterism in Ursa Major. The two stars on the right, Merak and Dubhe, are the Pointer stars. Also notice the dual star Mizar and Alcor in the saucepan's 'handle'. Image: Nik Szymanek.

Allow you gaze to fall on the two bright stars that make up the right-hand side of the pan. These are Merak and Dubhe, and we call them the 'pointer stars', because if you draw an imaginary line up through them and carry on going higher into the sky by about four times the distance between the two stars, you will come to the famous Pole Star, Polaris.

Now swing your gaze around to the south, and you can't fail to miss the stunning sight of Orion and in particular its trio of Belt stars (they depict Orion's actual belt, from which hangs his 'sword' which extends down to a fuzzy patch of light that we call the Orion Nebula), and bright red star Betelgeuse on the Hunter's top left shoulder and brilliant white Rigel on his right knee. Betelgeuse is what we call a red supergiant. It is a star that is 1,600 times bigger than our Sun but because it is 640 light years away (a light year is the distance that light, travelling at 300 million metres per second, travels in a year) it only appears to us as a brilliant point of red light.

Orion
The constellation of Orion. Betelgeuse is at top left, Rigel at bottom right. Image: Steve Richards.

Rigel is also a supergiant star, but is white in colour instead, which implies it is younger than Betelgeuse. Rigel is so bright that it is the seventh brightest star in the sky, even though it is 900 light years away. But the brightest is Sirius, the Dog Star, just to the lower left of Orion in the constellation of Canis Major, which is one of Orion's hunting dogs (don't worry about spotting the pattern of stars that makes up Canis Major; aside from Sirius none are particularly bright, especially as they are low down, and Sirius is bright enough to be noticeable on its own). Above Sirius is another bright star called Procyon, found in Orion's other hunting dog, Canis Minor. An easy way to make sure you are looking at Sirius, and not Procyon, is to draw an imaginary line from the Belt stars south-east by about the distance of two fists held at arms length, and you'll arrive at brilliant Sirius. (Move the line the other way and you come to red Aldebaran in Taurus.)

Cassiopeia
The familiar W shape of Cassiopeia. Image: Nik Szymanek.

Now turn around to face north, and look high overhead. Do you spot a group of five stars arranged in a rough 'W' shape? This is Cassiopeia, the Queen of Aethiopia who was mother to Andromeda, saved in the mythological legend from Cetus the Sea Monster by Perseus and his winged steed Pegasus - the mythological story is played out every night in the autumn and winter once the Sun sets! Andromeda lies directly beneath Cassiopeia, sharing stars with Pegasus, whose main stars form a large and noticeable square (a good test of how dark your observing location is is to count how many stars you can see inside the square). On the other side of Andromeda is her saviour, Perseus, and you may spot bright Mirfak and Algol, the latter of which is known as the 'Demon Star' on account of its winking in brightness - Algol is in fact what is called an eclipsing binary, which means it has an unseen companion that blocks some of its light, causing it to dim periodically just under every three days.

If you can follow the sky around a short way to the south-east you'll spot bright yellow Capella, the sixth brightest star that you can see from the Northern Hemisphere. Capella is only 42 light years away, and lives in the constellation of Auriga, which has a rough boxy shape. Capella is actually a double star, with two stars orbiting one another, but they are so close together that to our eyes they appear as a single star. Drop southwards and you'll spy the Seven Sisters of the Pleiades Cluster, which is part of Taurus the Bull, along with Aldebaran.

The Moon and planets
This whistle stop tour of the constellations doesn't bring an end to your naked eye pursuits. During evenings this January, high in the sky, you will see a bright object in the midst of the constellation of Taurus, close to the Pleiades. This is Jupiter, the biggest planet in our Solar System. The planets, unlike the stars, don't remain in fixed positions relative to one another. Instead they wander around (the word 'planet' is derived from the ancient Greek for 'wanderer'), and move through different constellations each year. You can't see any detail on them with you unaided eye, but they are pretty to look at nonetheless.

Then of course there is the Moon, which you cannot fail to notice! The Moon, of course, orbits the Earth and is clearly large enough to some some features on its silver disc, even without a telescope. Those dark areas, that mark out the 'Man in the Moon' (some contend that you need a very vivid imagination to see a face in the pattern!) are called maria (singular: mare) and are vast lava flows that dried up billions of years ago, caused by mighty impacts that smashed into the Moon (and indeed Earth, but on the Moon there is no erosion or weathering to wipe away the evidence). The bright areas are more ancient highlands. The Moon is absolutely littered with craters, but none of them are really big enough to be seen with the naked eye.

Phases of the Moon
The changing phases of the Moon, from left to right: crescent, first quarter, gibbous, full and last quarter. Images: Jamie Cooper.

The next thing that you'll notice about the Moon is that it changes shape. It looks like it is being gobbled up, but the Moon is still there (look closely and on the dark parts of the Moon, you will be able to see a faint glow - this is reflected light from Earth, and we call it Earthshine). Nor is it anything to do with lunar eclipses. All that is happening is we are seeing the night-side of the Moon, while the part lit up (be it crescent, half, gibbous or full moon) is the dayside part. The Moon always shows the same face to us, but the far-side of the Moon isn't necessarily dark - it can be daylight there too. The Moon takes about 27 days to undergo this series of phases, from 'full' (when we can see the full disc of the Moon), to gibbous (when the dark part is crescent shaped) through to 'last quarter', to crescent (when the dark side is gibbous shaped), to new moon (when the Moon's face is all dark, and it is daylight on the far side of the Moon that we cannot see) to 'first quarter' and then back to full.

Meteors, too, may also be spotted flashing through the sky, either sporadically or during meteor showers that occur at the same times each year. And then there is perhaps the best sight in the entire night sky, if you can find a dark location away from any streetlamps, house lights or security floodlights in towns and cities: the Milky Way, a shimmering river of thousands upon thousands of twinkling stars, running through Auriga and Cassiopeia in the winter, and Cygnus and down to Sagittarius in the south in summer. This Milky Way is our Galaxy, seen from within. An amazing, unforgettable sight, and if ever you are in the dark countryside at night, make sure you take the chance to gaze up at this majestic vista.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
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Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
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3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
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