Mars is one of the brighter planets and you will have no problem finding it in the heavens when it is in a dark sky and looking like bright red or yellow star.
It does, however, vary considerably in brightness because its distance from us changes hugely over time. Here is a guide on how to find Mars and what you can expect to see.
Mars is the next planet out from the Sun after the Earth but its year is roughly twice the length of our own. This means that our two worlds come close every couple of years but, a year later, are widely spaced on opposite sides of the Sun.
When far apart, Mars appears like a fairly average bright star. At its closest, it shines as one of the brightest objects in the sky and its reddish colour will be quite apparent.
Mars has an eccentric orbit around the Sun. Because of this, its distance from Earth varies enormously from one approximately two-yearly close encounter to another. That of 2003 was particularly close and it came to a distance of 56 million km (35 million miles).
However, in March 2012, it came no closer than 101 million km (63 million miles). Since 2012, closest approaches have become more favourable, and in July 2018 Mars lay less than 58 million km (36 million miles) from us. After that, Mars becomes more distantly separated again through the oppositions of October 2020, December 2022, January 2025 and February 2027.
Astronomers talk about brightness as a number called magnitude. The higher the number the fainter the object. Each whole number is about 2.5 times brighter or fainter than the next. The brightest stars in the sky are around magnitude 1. The faintest you can see without a telescope on a dark night are around magnitude 6. The Sun shines at a minus magnitude, -27. Against this scale, Mars’ brightness varies from about 2 when it is at its furthest from us to a brilliant -3 when at its very closest.
Our charts show the path of Mars as it slowly brightens on its next approach to Earth. After passing behind the Sun, it becomes visible in the morning sky before dawn in October 2019, and then gradually becomes more easily visible and brightens as it heads towards its next closest approach to Earth.
Opposition (the date when the planet lies on the other side of the Earth to the Sun) will occur on 13 October, 2020, when the planet will reach a magnitude (apparent brightness) of -2.6 in the constellation of Pisces. It will actually have been at its closest to Earth a few days earlier, on 6 October. The reason why the dates of Opposition and closest approach do not coincide is because Mars’ orbit is eccentric – in other words oval and not circular.
Around Opposition, Mars will be seen to perform a curious loop in the sky. Astronomers call this retrograde motion. There is no trickery on Mars’ part – this happens when the faster-moving Earth overtakes the Red Planet on the inside track. It is a bit like passing another car on the highway – you are both heading in the same direction but the other vehicle appears to slip backwards against the background.
What you can see
Mars certainly puts on a great showing for anyone observing with their eyes alone – and it can be fascinating to follow its gradual movement against the starry background from night to night.
Binoculars will help to emphasise the planet’s rusty orange colour but to see any detail you will need to look through a reasonable size amateur telescope. And even then, don’t expect to see a lot – for at its best, Mars only ever appears smaller in the sky than the giant planet Jupiter.
In October, 2020, Mars grows to an apparent diameter of 22.6 arc seconds. You will need a reasonable magnification to see any detail on Mars – at least 40x – the actual power you can use will depend on the atmospheric conditions, or “seeing”, and the size of telescope you are using. At best, magnification of 40x will show an image of Mars the size of an orange viewed with the eye alone across the length of a tennis court.
You may be able to make out dark markings on Mars, unless a dust storm blows up, as happened in June 2018 shortly before the last Opposition – and what is left of the southern polar cap. You may even be able to follow the rotation of Mars. Its day is similar in length to our own.
To keep Mars in your telescope’s field of view as the Earth rotates, a planetary observer’s telescope will probably have a motorised drive to turn it. Many modern telescopes today have mini computers in their drives which will actually find Mars – and virtually anything else in the sky – for you.
Some amateur astronomers today are using CCD cameras, digital cameras and even webcams to record images of Mars. With the aid of computer processing, remarkable amounts of details can be seen on many of these.