An Introduction to Astronomy & the Solar System

Astronomy is certainly the oldest of all the sciences, and is an exciting voyage of discovery. The night sky has fascinated people since before the dawn of civilisation, with the heavens remaining mysterious, awesome and fascinating.

Early civilisations in China, Egypt and the Middle East divided the stars up into groups or constellations, and recorded spectacular phenomena, such as comets and eclipses. With the Greeks, came the first really major advances. The first of the great philosophers, 'Thales of Miletus', was born around 624 AD. A clear distinction was drawn between the stars, which seemed to stay in the same position relative to each other, and the 'wanderers' or planets, which shift slowly from one constellation to another.

Aristotle, who lived from around 384 to 325 BC, gave the first practical proof that the Earth is a globe, and in 270 BC, 'Erathosthenes of Cyrene' measured the size of the globe with remarkable accuracy.

Not until the early 17th Century did the night sky begin to give up some of its secrets. Galileo (an Italian physicist and astronomer), trained his telescope on the heavens, and observed moons orbiting Jupiter and phases of Venus. This was the beginning of an age of astronomical enlightenment, that in turn saw Kepler explain the motion of the planets, Newton elaborate the phenomenon of gravity, and Herschel discover Uranus.

It was not until Friedrich Bessel (a German astronomer) in 1838, determined the distance to a nearby star, 61 Cygni, that the enormity of the stellar Universe became apparent. Then, early this century, Hubble proved that spiral nebulae are separate island galaxies, millions of light years away. Consequently, the Universe began to assume dimensions beyond the grasp of the human mind.

Astronomical Equipment

You can enjoy many hours of observation and see thousands of stars with no equipment at all, and this is how most amateurs start out. Despite this, binoculars and telescopes are useful, and allow you to see more objects in the sky, and to examine them in more detail.

Binoculars are compact, and although they are not as powerful as a true astronomical telescope, they have the great advantage of portability and comfortable viewing with both eyes. An ordinary pair of binoculars will reveal about 30 stars, for every single star seen with the naked eye. They must be held steadily on a solid support or tripod, otherwise the stars will appear to jump around, as a result of the body's heartbeat and muscular tension.

Binoculars do not provide very high magnification, so they will not reveal planetary details, although good ones will show 3 or 4 satellites of Jupiter and the crescent phase of Venus. The larger craters on the Moon can also be seen.
If you are thinking about buying a telescope, it would be advisable to get an experienced observer to have a look through it, before you finally decide. If you purchase a poor telescope, consequently you could be turned off Astronomy before you've even begun.

Aperture and Magnification

Binoculars and small hand telescopes belong to the same family of low-power instruments, with the most important features being the aperture and magnification. The aperture is the diameter of the objective lens, at the front of the instrument, which is usually between 30 and 50 mm. The larger this lens, the brighter the image, since more light is being collected.

The magnification indicates how much larger an object looks. The Moon is half a degree across in the sky, so through a x10 telescope, it will looks five degrees across. The higher the magnification, the smaller the field of view.

The Constellations

Throughout the centuries, people have looked to the stars to help them navigate across open oceans or feature less deserts, know when to plant and harvest, and preserve their myths and folklore. The ancient people used the appearance and disappearance of certain stars over the course of each year, to mark the changing seasons. The brighter stars were grouped into readily recognisable shapes, the constellations, in order to make it easier for the people to interpret this celestial calendar.

Our modern constellation system comes to us from the ancient Greeks, and Astronomers officially recognise 88 constellations, covering the entire sky in the northern and southern hemispheres. It is important to realise that the great majority of star patterns bear little, if any, resemblance to the figures they are supposed to represent. Therefore they were probably meant to be symbolic, not literal, representations of the individual's favourite animals or heroes.

Finding your way around the night sky

At first, star maps can be very confusing for the beginner, so a good way of avoiding disappointment is to learn to look for some of the brighter stars. When you are familiar with these, the other patterns will be easier to find. The constellations of 'Ursa Major' (the Plough) and 'Orion' are so well known that they can be used to identify other stars and groups. 'Ursa Major' is in the northern part of the sky, and is circumpolar for much of Europe and the USA. 'Orion' lies on the celestial equator, and is visible everywhere in the world between September and April. Once you have identified a few of these brighter groups, consequently, the fainter constellations can be fitted into the gaps quite easily, using simple star maps.

Observing the Night Sky

How well we see a star depends on how bright, and how far away from Earth it is. This is measured and known as magnitude. Magnitude is relative, the lower the measurement, the brighter the object. Some objects are so bright that they have a negative magnitude number. The Sun, for example, is -27 and the full Moon is -13.

How much you are able to see in the night sky is subject to where you live. If you live in a city, or close to one, the lights from the city will make the sky background bright. As a result, the lack of contrast will prevent you from seeing more stars. Therefore, the best place to observe stars is in an open area, away from any city lights on a clear night. Under optimum conditions, you may see stars as faint as magnitude 6. If you use binoculars, you may see to magnitude 8, and with a six inch telescope, you may see as high as magnitude 13.

Observing the Planets

The planets are always fascinating to watch, as they are never in exactly the same position from night to night, due to their orbital motion around the Sun. Mercury through to Saturn are visible with the naked eye, and Uranus and Neptune can be seen with binoculars. Pluto is the only planet which requires a proper astronomical telescope of about 250 mm aperture.

The different planets move in different ways. Mercury and Venus, the inferior planets, are a special case, as their orbits lie inside that of the Earth, therefore they are always in the neighbourhood of the Sun.

Mercury
Mercury lies within 28° of the Sun, and from the northern hemisphere, the best time for hunting it is from January to April, as an evening object, and from July to October, as a morning object. Mercury appears white, but when looking for it in the evening, the sky often colours it pink.

Venus
Venus is much easier to see than Mercury, and near elongation, it can be made out in the daylight sky. Between elongation and inferior conjunction, the crescent phase can be seen using firmly mounted binoculars. During the mid-crescent stage, Venus is at its brightest, therefore this would be the best time to seek it with the naked eye in daylight.

Observing Venus through a telescope isn't ideal, because its brilliance dazzles. Therefore, the best time would be in bright dawn or dusk, when it begins to be easily detectable with the naked eye. Around the time of superior conjunction, Venus is usually lost from view for about four months. Despite this, it sweeps through inferior conjunction so rapidly that it reappears in the morning sky, only a matter of days after vanishing in the evening twilight. Therefore, Venus is called the morning or evening star, according to when it is visible (even though this is not true, as Venus is a planet, not a star!)

Mars
Mars is the only planet in the Solar System that gives us a reasonable view of its true surface, due to its very thin atmosphere. Mars comes to opposition every 26 months or so, but its orbit is so eccentric that some apparitions bring the planet much closer than do others. As a result, observing Mars can be frustrating.

Really favourable oppositions occur at intervals of about 17 years, with the last occurring in 1986. Mars approaches and recedes very rapidly, so when it appears you have to make the most of it. With telescopes of 60 mm aperture, you can make out dark markings and the polar caps.

Jupiter
Jupiter is ideal for the amateur to observe, as its disc is always large, and its four bright satellites can be seen using good binoculars. With an aperture of 60 mm and a magnification of about 100, you can see visible details on the upper cloud layer. The belts show wisps and irregularities, and the famous 'Great Red Spot' can be seen, when it is prominent.

Jupiter spins so rapidly that its disc is noticeably flattened at the poles. The four largest satellites, Io, Europa, Ganymede and Callisto, can also be observed as they move around the planet.

Saturn
With the naked eye, Saturn looks like a yellowish star of about magnitude 2. Saturn spends over two years in each constellation, as it takes almost 30 years to pass around the Zodiac once. Saturn's rings can be made out with a magnification of around 50, unless they are almost edge-on. When the rings are wide open, 'Cassini's Division' can be made out in a small astronomical telescope.
With good binoculars, Titan can be made out, and with anything more powerful, other moons can also be identified. It is usually difficult to make out any markings on the disc itself, apart from a brighter equatorial zone and dusky poles.

Uranus and Neptune
Uranus is just visible with the naked eye, and both Uranus and Neptune can be observed with binoculars, providing their positions in the sky are known. To know which part of the sky to begin searching for them, you will need to refer to astronomical yearbooks.