Mars, the red planet, holds a great fascination for humans. Associated with the God of War, this fascinating world has been the subject of endless speculation on whether life once inhabited it, and is currently the target of a bevy of spacecraft making for its frigid and arid surface.

This year is the best opposition of Mars since 1988, and this is an excellent opportunity for people to observe this fascinating world. What is an opposition? Opposition refers to when a planet is opposite the Sun in the sky, this can only happen to outer planets, as Earth must pass between the Sun and the planet. The Earth passes Mars in its orbit every 26 months, and at this time we get a good view of the Red Planet. So why the fuss this time?

When Mars is also making its closest approach to the Sun, our view is very good indeed. While Mars is on average 228 million km from the sun, due to Mars's elliptical orbit this varies by 42 million kilometers. If Mars is at its furthest from the Sun at opposition, Mars is also around 99 million km from Earth, while if Mars is at its closest to the Sun during opposition, this value narrows to only 57 million km. Favorable oppositions occur only once in every 15 to 17 years. This years is not only the best for 15 years, it is also the best for thousands of years, with Mars a mere 55.8 million km apart. This degree of closeness will not be achieved again until 2287.

Oppositions in the early months of the year, when Mars is furthest from the Sun, are allways poor. The best oppostions occcur around August. This is very good for Southern observers, as Mars is high in the sky, and the winter sky is usually still and transparent, ideal conditions for watching Mars. During this years opposition, the visible disk of Mars increases in diameter, from 5 arc seconds, to 25 arc seconds (an arc second is approximately 1/3600th of your fingerwidth). While this sounds astoundingly small, 25 arc seconds will give quite a substantial disk in most amateur telescopes, even the small ones from Tasco.

What you can expect to see

Telescopes Mars shows clearly visible markings in a 50 mm refractor telescope, and significant detail can be seen in a 4" reflector, while 6" and 8" instruments will give better detail still. No current Earth-bound telescope can reveal the huge volcano, Mons Olympus, or the huge valley of Vale Marensus, which are seen in many of the spacecraft images. However, significant features such as Syrtis major (featured in the Masthead graphic) will be visible in even a small telescope. The Martian day is about 40 minutes longer than the Earth day, so if you observe at the same time each night, you can see the surface features rotating into and out of view. Dust storms can also occur, sometimes lasting days. Wind removal and deposition of the reddish, iron rich dust can also reveal or obscure features, so Mars's appearance can be somewhat different between each opposition. Seasonal winds alternately covering and uncovering darker features with lighter dust were once interpreted as seasonal plant growth. Studing the Martian storms and the changing surface features is a valuable amateur activity.

In the May 2001 issue of SKY & TELESCOPE (pages 115 to 123), Thomas Dobbins and William Sheehan discussed rare historical observations of bright, star-like flares from certain regions on the planet Mars. They suggested that the flares might be caused by specular reflections of sunlight off water-ice crystals in surface frosts or atmospheric clouds, specifically at times when the sub-Sun and sub-Earth points were nearly coincident and near the planet's central meridian (the imaginary line running down the center of the visible disk from pole to pole). In 2001 flashes were seen by observers in the US in Edom Promontorium, near the Martian equator.

In late July and early August this year, conditions to see these flashes will occur again at a Martian latitude of 20°. By then Mars's apparent diameter will exceed 20 seconds of arc. Between July 24 and August 10, observers should keep an eye on northern Thaumasia, northern Solis Lacus, southern Tithonius Lacus, Deucalonius Regio, Iapygia, and northern Hellas all at or near latitude 20°. It will be interesting to see if flashes like those observed at Edom in 2001 are rare events, meaning that site is special, or if they can be seen at many locations whenever the Mars-Sun-Earth geometry is favorable. For more information see this Sky and Telescope article.

So August (and before August if you want to watch Mars's disk grow) is an excellent time to dust off that old telescope lying around in the garage, or to beg a view from a friend or neighbour with a telescope. Better yet, many astronomical clubs hold open nights, and this is an excellent opportunity to see this fascinating world in a decent telescope. Also, some of the local planetariums may be showing off Mars if they have telescopes (See the Links section for addresses).

For recording the apearance of Mars, all you need is a sheet of paper on a sturdy back ground, a pencil (or coloured pencils if you want to try recording the colors you see), a small torch coverd in red cellophane and a watch. Make sure you and your telescope are located in a relatively dark place, and have modest circles predrawn on your paper (I use a 20 cent piece). Have your telescope out for a while beforehand so that it is at ambient temprature, to prevent air currents in the telescope from ruining the image. Record the date and time, and the weather (if it is windy, how much cloud, how much moonlight, what is the dimmest star you can see, etc.). Make sure you are wearing warm clothing, then make yourself comfortable at the eyepiece, preferably with a chair that allows you to sit and view comfortably, and, well, start drawing. It may take a few trys before you get the hang of recording what you see by red light, but you will feel a warm glow of accomplishment when you can. The Ephemeris below gives the time Mars rises, its magnitude, and its altitude at midnight (5 degrees is equivalent to the distance covered by an outstreached hand), and its aparent diameter in arc seconds.