Orbits of Earth and Mars
This article is the text of the Society's leaflet about the opposition of Mars. Pick up some copies at for your friends.
The Observatory will be open to the public in the evenings from Saturday 23rd to Friday 29th August to coincide with National Astronomy Week. There will be an exhibition about Mars and illustrated talks. Weather permitting, we will also be observing Mars through the main telescope.
For further information see our website at www.astronomyedinburgh.org/mars or check the answering machine at 0131 556 4365.
Orbits of Earth and Mars
Mars takes 687 days to travel round the Sun, compared with Earth's 365 day year. Once every two years or so, Mars catches up with the Earth to take up position opposite the Sun in our sky - opposition. This is the best time for viewing the planet from Earth as it is visible all night. The actual date of opposition (August 28th) is not crucial, as the weeks either side should provide excellent opportunities for observation.
Mars brightens rapidly towards opposition and its apparent size increases as the distance between Mars and the Earth decreases. The next illustration shows this increase in size and that, just like the moon, the phase also changes. During opposition, we see "Full Mars", but, unlike the Moon, the phase never gets any less than around 85%.
Relative Size and phase of Mars at 4 week intervals from 8/6/2003 to 23/11/2003
This year, Mars is not only at opposition, but the relative placing of the two planets means that its distance from Earth falls to around 35 million miles (56 million km) - its closest since records began. The "Red Planet" will appear bigger and brighter than at any time for more than a thousand years!
The map shows the night sky looking South around midnight on the 28th August, 2003 - the day of opposition. Mars will be the brightest object in the sky and, due to its red colour - unmistakable. High above, to the South West will be the "Summer Triangle" made up of the bright stars Deneb, Altair and Vega.
The following table indicates the rise, set and transit times either side of opposition. The transit time is the time at which the planet is due South and at its highest elevation above the horizon - the best time for observation. After opposition, Mars rises earlier and transits during the evening - a much more sociable proposition. However, for telescopic observation, the disc of the planet will also be getting smaller as the Earth pulls ahead in its orbit and the distance between the two planets increases again.
| Sun | Mars | ||||
|---|---|---|---|---|---|
| Date | Rise | Set | Rise | Transit | Set |
| 29/06/03 | 03:30 | 21:02 | 23:40 | 04:18 | 08:53 |
| 27/07/03 | 04:07 | 20:30 | 22:09 | 02:51 | 07:29 |
| 31/08/03 | 05:14 | 19:11 | 19:49 | 00:13 | 04:31 |
| 28/09/03 | 06:09 | 17:57 | 17:40 | 21:59 | 02:23 |
| 26/10/03 | 07:06 | 16:47 | 15:41 | 20:27 | 01:15 |
Times are GMT - please add 1 hour for BST for the first 4 dates
Mars will be easily visible to the naked eye as a bright, red, steady, star-like object in the night sky. Binoculars do not magnify a great deal and may not even show Mars as a small disc rather than a point. However, they can be used to track the planet as, week by week, it slowly moves through the constellation of Aquarius. Even at opposition Mars is a difficult object to observe. It will never be higher than about 20° above the horizon and the disc will still be very small at 25 arc seconds (0.007 degrees) - around half the apparent size of Jupiter. A good amateur telescope should provide views of the main surface markings, such as the V-shaped, raised plain of Syrtis Major. Atmospheric conditions on Earth and Mars can have a major impact on observing, however. During the last opposition in 2001, all surface detail was obliterated by a massive sand storm which covered the planet for several weeks!
We hope to arrange public viewing through the Societys 6" Cooke refractor on Calton Hill. Unfortunately the best views should be had around 1.30 am. during the weeks either side of opposition. This will improve after opposition.
Come to our exhibition. We have also produced a more detailed, 6 page observing guide which is available from the Society. Come to our monthly meetings - visitors are always welcome! Check out magazines such as Astronomy Now, Sky and Telescope and Astronomy.