Saturn

Saturn is the second largest of the gas-giants and telescopically the most beautiful of the planets. This is because Saturn has a ring system comprising of trillions of moonlets made of water ice and can be easily seen with quite a modest telescope. Binoculars will not show the rings but rather show Saturn as a bright yellow oblate blob, however a telescope will reveal the Cassini division in the rings and possibly some faint cloud structure.

Image: Saturn's position (ringed in red), as of 17 May 2009, among the outer planets in the Solar System. Image created with Solar System Simulator V4

The Earth

At about 93 million miles from the Sun lies the orbit of our planet Earth. Earth is the largest of the terrestrial planets and the only planet known to support life.

The Earth has an atmosphere which consists of 78% nitrogen, 21% oxygen and 1% argon and other gases [1] and water oceans which cover 71% of the Earth's surface [2].

The Earth has only one natural satellite, the Moon (or Luna) but has thousands of artificial satellites and on a clear night many of these can be seen just by looking up into the night sky. An artificial satellite may look like a faint dot moving between the stars or may appear as bright as the planet Venus in the case of the International Space Station.

Earth, The Blue Planet, is our home but observation of the Earth as a whole can of course only be acheived by leaving it's surface. There is one way however we can observe the Earth's disc and that is by viewing a lunar eclipse. This is because we are seeing the Earth's shadow pass over the surface of the Moon.

References

[1] http://www.nasa.gov/audience/forstudents/9-12/features/912_liftoff_atm.html

[2] Atlas of the Skies - ISBN 1-84406-011-X

Mars

Mars, named after the Roman god of war, is the fourth planet from the Sun and the last of the inner terrestrial planets. Out of all the planets of the Solar System Mars is the most 'Earth-like' having a thin atmosphere, polar icecaps, an axial tilt similar to Earth's and a similar length of day. That said it is still a pretty inhospitable place so only space probes have landed there so far.

Through a low power telescope Mars may appear as a rusty orange/red coloured disc with patches of grey.

Mars has two natural satellites, Phobos and Deimos translated as 'fear' and 'panic'!

Mercury

Mercury, smallest of the terrestrial planets and closest to the Sun. With it's orbit being so close to the Sun it is a tricky object to spot and it can only be see just after sunset or just before sunrise. As it is eay to mistake Mercury for a star the best way to find it is to check star charts or use a piece of software such as Redshift or Stellarium to find it's location.

Finding Mercury can be made easier if it happens to be near another brighter planet in the sky (see image below) then it is just a matter of locating the brighter planet to find Mercury nearby.

The above image is a reconstruction of the positions of Venus, Mercury and Jupiter as they appeared in the sky on 2 Jan 2009. Mercury can be seen just a few degrees from Jupiter.

Mercury's orbit is inside that of the Earth's so it can also be seen as a silhouette when it transits the Sun.

Venus

Venus, named after the Roman goddess of love, is one of the inner terrestrial planets. Venus' orbit is the second furthest from the Sun after Mercury and closer to Earth's orbit than any of the other planets.

Venus' has a thick atmosphere of mostly carbon dioxide with some sulpher dioxide, this means that Venus is completely covered with cloud at all times and virtually no detail can be seen with standard ground based telescopes. It also means Venus has a high albedo (it relfects light really well) so that when Venus is at it's closest to Earth in it's orbit it is the third brightest object in the sky after the Sun and Moon. If you know where to look it can even be seen in broad daylight!

From the Earth, the planet Venus goes through phases just like the Moon and for a similar reason. When Venus is at it's closest to Earth it is between the Sun and Earth so most of the light from the Sun falls on the side of Venus which we cannot see and we see a crescent. When Venus is furthest from the Earth more of it's disc is revealed as light from the Sun is falling on the side of Venus we can see. However, it is when it is in it's crescent phase that Venus is at it's brightest as that is when it is at it's closest to us.

Venus is best spotted after sunset or before sunrise depending on where it is in it's orbit.

Transits

A transit occurs when an object in space passes in front of another one. An example of a planetary transit occuring is, when viewed from the Earth, the planet Venus passes in front of the Sun's disc and can be seen as a small black disc on the Sun's white disc.

Transits can also be seen with the planet Mercury passes in front of the Sun. This is because the orbits of Mercury and Venus are inside that of the Earth so at certain times those planets will pass between the Sun and the Earth. Transits of Mercury or Venus cannot occur every year however, this is because the planets orbits are on a different plane to that of the Earth's, in other words they only line up at certain times.

The orbits of Mars, Jupiter and Saturn lie beyond that of the Earth so a transit with the Sun cannot occur since those planets never pass between the Earth or the Sun.

However, with a telescope we can see a transit occur when the moons of Jupiter or Saturn pass in front on those planets.

Eclipses are similar to transits except that the object in front completely covers (or significantly covers, in the case of a partial eclipse) the object furthest away. For example the Moon is said to eclipse the Sun when it passes in front of the Sun's disc. The Moon appears so much larger when it passes across the Sun's disc compared to Venus because it is so much. closer.

An occultation is also similar the difference being the object in front appears to be larger and will partially cover the object further away. For instance the planet Saturn passing behind the Moon.

Jupiter

Jupiter is the largest planet in our solar system. It can be easily seen with the unaided eye looking like a very bright star. Through binoculars the four Galilean moons can been seen and Jupiter's disc can be resolved. A modest telescope will reveal banding on Jupiter's disc and you may even see the Great Red Spot if you observe Jupiter for long enough as the largest planet only takes about nine hours to complete one rotation, or one Jovian day if you like, quick enough to see the whole of Jupiter in one night!

Notable Features

Galilean Moons

Great Red Spot