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. Currently a bevy of spacecraft are circling its frigid and arid surface taking detailed images and probing Mars's atmospheric composition. They will be joined by three new spacecraft which will investigate Mars's atmosphere further as well as subsurface composition and look for past life. The robot explorer Opportunity which ranging over Mars's surface for for 14 years was lost in the 2018 global dust storm. The Mars rover Curiosity now has 8 years of exploring the red planet. Curiosity will be joined by the Perseverance rover and its helicopter and the Tianwen-1 Lander and rover. The search for evidence of life on Mars and a possible sample return makes this oppositions missions very exciting.

This year is a average opposition of Mars. Not as good as the opposition of 2018 or 2020, But there won't be a better one one until 2033. Nonetheless this year is still a good 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.

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. During the Great Opposition of 2003, Mars and Earth were a mere 55.8 million km apart. This degree of closeness will not be achieved again until 2287. This year, Mars and Earth will be 81.5 million km (0.54 AU) apart.

Oppositions in the early (or late) months of the year, when Mars is furthest from the Sun, are always poor. The best oppositions occur 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. This years opposition occurs during December. Summer is not as ideal as winter, with poor conditions for Southern Observers. The warm nights makes observing more comfortable, but atmospheric turbulence is likely high, with Mars never rising high above the horizon. Although the skies are likely to be clear, Mars's markings may be harder to distinguish. The visible disk of Mars increases in diameter, from 5 arc seconds, to 17.3 arc seconds (an arc second is approximately 1/3600th of your finger-width). While this sounds astoundingly small, 17.3 arc seconds will give a significant disk in most amateur telescopes, even the small ones from Tasco. Mars will be 1/76 th of the diameter of the Moon, about 2/3 the diameter of Jupiter and a trace bigger than the diameter of Saturn (Saturn itself, not the ring system, which is larger) This year, the Opposition (December 8) is later than the closest approach of Mars to Earth (December 1).

What you can expect to see

Mars is in the readily unrecognizable constellation of Taurus the Bull. At opposition Mars is below the bright red star Aldebaran and the distinctive "V" shape of the Hyades cluster. It is also close to the iconic constellation of Orion with it's distinctive belt and Mars, Aldebaran and the red star Betelgeuse form a triangle. Mars will head towards the beautiful cluster the Pleiades during December ad the first half of January, then moves aback down the Horns of the Bull. Mars is in retrograde motion at the moment, and occurs due to Earth overtaking Mars in its orbit. A map showing this motion is here.

Telescopes The best time to observe Mars is when it is highest in the sky, unfortunately this occurs well after midnight for a large proportion of best viewing times, and not long after midnight for the rest. Be prepared for some late nights if you want the best telescopic views (see the Ephemeris below, Transit times are when Mars is highest).

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. However, be aware that large dust storms may errupt, and for the 2018 Opposition Mars was a featureless ball for a lot of the time. No current Earth-bound telescope can reveal the huge volcano, Mons Olympus (other than a faintish darker spot on the surface), 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 (as I mentioned above). 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. Studying 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.

So December to January 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 appearance of Mars, all you need is a sheet of paper on a sturdy background, a pencil (or coloured pencils if you want to try recording the colors you see), a small torch covered in red cellophane and a watch. Make sure you and your telescope are located in a relatively dark place, and have modest circles pre-drawn on your paper (I use a 20 cent piece or my telescope eyepiece cap). Have your telescope out for a while beforehand so that it is at ambient temperature, 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 tries 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 outstretched hand), and its apparent diameter in arc seconds. For comparison the Moon is 1921.59 arc seconds across and Jupiter is currently 38.9 arc seconds across.

If you have a mobile phone, and a decent sized telescope, you may be able to snap images of Mars with your phone, there are now a variety of mobile phone attachments for holding phones to a telescopes eyepiece. Setting the phones camera app so that you see something other than a tiny overbright dot will require some experimentation.