Mars is the fourth planet from the Sun and has long intrigued mankind as possibly harbouring life and as an obvious destination for interplanetary travel. It can come closer to the Earth than any other planet apart from Venus, but being only about half the size of the Earth, it is surprisingly small and difficult to see for most of the time.
Mars has a thin atmosphere through which the planet's red surface is easily visible. Every two years two months Earth catches up with Mars and when it approaches opposition it becomes very bright and its orange-red colour is easily visible even to the naked eye. At this time a telescope reveals surface markings, polar ice-caps and sometimes clouds and dust-storms, but away from opposition the disk is so small that scarcely anything can be seen.
The orbit of Mars is quite elliptical so the distance at opposition varies between 57 and 99 million km. Unfortunately for observers in the UK the nearest oppositions, such as that in 2001, occur with Mars well south of the equator so the planet is low in the sky. Oppositions in later alternate years will be get progressively further away, but the view from the UK will improve as they occur with Mars higher in the sky.
Binoculars reveal the disk quite easily at opposition, but Mars' two captured asteroid moons, Phobos and Diemos, are too small to be seen except in a large telescope.
| Distance from Sun (Million km): | 207 (min) | 249 (max) |
| Min. Distance from Earth (Million km): | 57 | |
| Orbital Period: | 687 days | |
| Mean Interval between Oppositions: | 780 days | |
| Diameter (km): | 6,759 | |
| Rotation Period: | 24h 37m | |
| Apparent Diameter (arc seconds): | 25.7 (max), 3.5 (min) | |
| Max. Apparent Brightness (magnitude): | -2.8 |
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Jet Propulsion Laboratory Mars pages | |
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ESA Mars Express, with the UK's Beagle 2 lander, due to arrive Christmas Day 2003 | |
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NASA Mars Exploration Rover missions, due to arrive in January 2004 |
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