If you are middle-aged or older I am sure you will remember seeing live broadcasts of the Apollo astronauts walking on the surface of the Moon. I vividly recall those exciting times. Sadly for most of us, the thrill of watching broadcasts of humans landing on the ‘Red Planet’, Mars, is likely to be experienced by only the very youngest readers of this book.

By way of compensation there has been a recent surge in unmanned orbiting probes, landers and even surface-roving vehicles sent to Mars. We have discovered much about the planet as a result, though plenty more remains to be learned. There are indications that Mars has a dynamic early history and maybe its surface has seen even some significant changes in the relatively recent past. We telescopists cannot hope to answer the major questions but there is some active meteorology to be observed. There are also some slight transient changes together with some year-to-year minor variations in the surface features to record using our backyard telescopes.

THE NATURE AND ORBIT OF MARS

Mars is a small world, having an equatorial diameter of 6787 km and a mass of only about one-ninth of that of the Earth. Its axial rotation period is 24 hours 37 minutes, very similar to the Earth’s 23 hours 56 minutes.