Astronomy allows us to view objects millions of light years away, but some of the most interesting things in the night sky are the planets of our own solar system. As the planets are closer to the earth, they can be observed through most telescopes. The solar system is the collection of planets that circle the star we call the Sun. This group of planets are captured by the gravity of the Sun and travel around the sun at different speeds and various distances. The solar system also contains comets, asteroids, dust and ice. The space between the planets is a vacuum with no atmosphere.
To view objects in the solar system we can use the naked eye, binoculars and telescopes. With the naked eye we can see the planets that are close to us and the stars beyond the solar system. The stars are not part of the solar system although the planets do appear to be similar in size without the aid of a telescope. Different telescopes can provide a magnified view of the planets and allow the observer to see the face of the planet. Distant stars will always remain finite points of light in any telescope.
Refractor telescopes can provide a better image with greater clarity and sharpness of detail. Reflector telescopes with larger apertures can see the distant planets that are small with low contrast.
Planets move around the Sun at different speeds and at different distances with respect to the Sun. Mercury and Venus are closer to the Sun, therefore are always found not far away from it.
Mercury and Venus are always seen before the Sun rises on the eastern horizon or after the Sun sets on the western horizon. This will depend on the position of the planet at the time and when the planet moves in front or behind the sun we cannot see it at all.
The planets on the side of the earth furthest from the Sun will be slower to traverse the sky and appear to follow the earth’s position allowing them to stay visible longer. As their orbit about the Sun is different to the Earth, their position against the stars will change slightly every night. As all the planets travel around the Sun on a similar plane, they all appear close to the central line in the sky known as the Ecliptic.
To know where and how to locate a planet observers rely on books, magazines, almanacs and computer programmes to know where and when they will be visible. The large planets such as Jupiter and Saturn are very bright and can be found in a general area if you know when and where to look. Distant planets such as Uranus and Neptune are very small and can only be found with good navigation skills and a telescope. For the best results, select a dark observing site on a clear night and research the position of the planet by the constellation it will be passing through. Find a dominant star in that constellation and pick a route to follow by star hopping. Generally this will help you locate the faint objects and planets that you are looking for.
Extended information on solar system science and exploration is available from the NASA Eyes on the Solar System site.