“Mars is a dynamic world, and over the next few months there will be some fascinating changes occurring on the Red Planet”

his October, the planet Mars came to opposition and was the best it has been in UK skies for many years. Looking like a brilliant glowing coal, it was quite unmistakable high up in the dark evening skies. As planet Earth is now moving away from Mars, it continues to get smaller and fainter, and you might think that there is little left to explore. However, nothing could be further from the truth – it will remain high and bright in the evening skies for months to come; for many its appearance at a more convenient time in dark evening skies will be the time when it really grabs the attention.

Mars is a dynamic world, and over the next few months there will be some fascinating changes occurring on the Red Planet. By the end of the year Mars will have an apparent diameter of 11 arcseconds – still big enough to be noticeable to naked-eye and binocular observers. Users of small

Tto medium telescopes will find that the Red Planet’s respectable diameter will be more than enough to follow the seasonal changes that are coming up, while owners of large telescopes will be able to follow for considerably longer as Mars remains above 6 arcseconds in diameter until the end of March 2021. Here we’ll highlight some of the seasonal changes you can expect to see with a telescope, and how best to go about observing them.

A Martian year

Mars has an axial tilt of some 25° and so it experiences well-defined seasons of winter, spring, summer and autumn as it moves in its orbit around the Sun. Just like Earth, opposite hemispheres experience opposite seasons: summer in the northern hemisphere means winter in the south. Since many of the changes on Mars are due to the changes in seasons, it is important that we keep track of exactly where we are in the Martian calendar at any particular time. Astronomers have devised a simple way of doing that – it’s called solar longitude, or Ls for short.

In the diagram above you can see that the Martian orbit is divided up into 12 intervals; Ls can be thought of as the angle made by Mars as it moves around the Sun. Astronomers take the autumn equinox in the southern hemisphere to be the value Ls=0° and our >