Magnificent Mars at its best
As the Red Planet makes its closest approach, reaches opposition and is occulted by the Moon, this really is Mars season! Charlotte Daniels helps you make the most of it
Seeing Mars through the eyepiece is always an unforgettable experience – whether it’s the first time or you’re revisiting an old friend. When conditions are right and you get a clear view, it’s almost as if you can reach out and touch the planet on the other side of the telescope. Planetary observing can throw up challenges of course. We are at the mercy of a number of conditions: distortions from Earth’s atmosphere, the brightness of the planet’s disc and its proximity to the horizon, and even the planet’s own weather can all affect the view we get, particularly for our rocky red neighbour Mars.
Nevertheless, don’t let this stop you taking advantage of the planet being well-placed in the sky, because this December brings the best conditions for viewing Mars until January 2025! On 1 December, it makes its closest approach to Earth. Then on the morning of 8 December, not only will it be at opposition but it will also be occulted by the Moon. But those aren’t the only opportunities to see this vibrant body, so join us as we tell you how to get the most out of Mars throughout December.
Mars at its biggest and brightest
The planet gets its time to shine as it sits directly opposite the Sun
Oppositions are exciting opportunities to see planets in a whole new light. They occur when a planet lies directly opposite the Sun, while we’re nestled in between. For this opposition, the arrangement is such that Mars rises at sunset and stays illuminated throughout the night before setting at sunrise – meaning there’s plenty of time to dodge clouds and dig out your telescope or binoculars for a look.
During opposition season, Mars’s full disc is illuminated by the Sun, granting us the best, most complete surface views. It can be a fickle planet to capture, its appearance changing drastically depending on its proximity, position and brightness. At its closest approach on 1 December it will appear the largest it has been since 2020, reaching an apparent size of 17.2 arcseconds across, dropping only to 17.1 at opposition on 8 December. At midnight, when it reaches its highest point above the horizon (30°), it will reach mag. –1.9, brighter than Saturn in the sky.
Mars season
Mars is on display for months after opposition
If the UK weather isn’t kind this December, don’t worry. Although it will be moving away from us, Mars isn’t leaving our skies for a while. Small refractors will still be able to see some surface details until the end of February 2023. After that, its angular diameter will mean it is more suitable for longer-focal-length reflectors until about April 2023. It will be visible until summer 2023, but its brightness and size will be much diminished.
It’s also a good time to see the other planets too, with Saturn, Jupiter, Neptune and Uranus lined up in the night sky, so why not put your planetary setup through its paces and see how many you can observe or capture in one night?
Occultation by the Moon
Mars will disappear from view for an hour on 8 December
Not only is Mars the largest and brightest it has been for over two years, but in the early hours of 8 December we will also see it appear to vanish behind our Moon. At around 04:57 UT, observers in the UK can witness the 100%-illuminated full Moon passing in front of Mars.
The planet will take around 36 seconds to disappear, before reappearing about an hour later at 05:57 UT. These timings are from the centre of the UK, but exact timings will depend on your location, so it’s wise to start observing earlier. While a bright Moon will wash out surface details on the approaching planet, it will provide a stunning view as Mars will be visible right up to the illuminated lunar edge. Turn to page 46 to find out more about the occultation.
Get your best view of the spectacle
Magnification, aperture, filters and seeing conditions all play a part
At the start of December, Mars is in the constellation of Taurus. Look to the east and then the south throughout the evening and it will be hard to miss. Mars can be enjoyed through almost any telescope; even a short, small-aperture refractor reveals details on the red disc. Adding a Barlow lens will increase the focal length and magnify the image, allowing you to pick up further details, including dark and light patches (known as albedo features). But the ability to magnify is limited by seeing conditions: the greater the magnification, the more disruptive atmospheric turbulence is. A (very) general rule of thumb for magnification is 20x to 30x per inch of aperture, although in reality it is very much down to the weather on the night.
A good-quality, longer-focal-length refractor could offer more surface detail, including some cloud structure or the polar caps. It’s worth noting that refractors are likely to require high-powered eyepieces in addition to a Barlow lens to get detail, adding more glass, which can end up distorting views or adding chromatic aberration.
Newtonian reflectors offer longer focal lengths and allow us to get closer. Catadioptric tubes, such as Schmidt- and Maksutov-Cassegrains, are longer still and allow the use of lower-powered eyepieces to achieve the same magnification. Lower-power eyepieces are generally easier to view through and provide better eye relief over higher powers. We suggest starting off with a low-powered eyepiece and stepping up to the point where views stop improving.
In all cases, coloured filters, which tend to screw into the base of an eyepiece, will help to boost surface contrasts. An orange filter is a good start as it neutralises the orange disc, allowing dark regions to stand out.
Don’t assume that 8 December should be the only date in your diary to view Mars. The weeks around opposition will also be a particularly special time to catch the planet. Taking time to view it during the week before and the week after opposition should not only allow you to see changes to the disc features, but will also train your eyes as you acclimatise to Mars’s surface.
It will also give you more chances for a prime viewing night as planetary observing very much depends on the atmospheric conditions here on Earth – and a clear night doesn’t always equate to good seeing. Air humidity, damp, weather fronts and even the jet stream’s relative position to you will have a significant impact on your session. If it’s poor one night, stick at it! The next evening can be very different and provides a good opportunity to compare any extra details you might see as you get to know the surface.
Mars’s changing orbit
No two oppositions are equal – some bring the planet closer than others
Mars oppositions occur roughly every 26 months and are a great chance to catch this challenging planet’s complex beauty. Not all oppositions are equal, however.
Both Mars’s and Earth’s orbits are elliptical, and each is gently affected by the gravitational pull of other planets, meaning that oppositions don’t always take place when Mars is as its closest point to us. This month, Mars will make its closest approach to Earth on 1 December, reaching a mere 81.45 million kilometres away. So-called ‘perihelic oppositions’ – ones where Mars is extremely close to us – only happen every 15–17 years or so. Even then, some perihelic oppositions are exceptional. For example, Mars’s opposition in 2003 occurred at the closest approach in almost 60,000 years, and won’t be beaten until 2287! In short, any opposition is an opportunity you’ll want to take full advantage of.
The variations also affect the planet’s apparent magnitude and the angular diameter of its disc. This year it will reach 17.2 arcseconds at closest approach, but in 2020 it was 22.6. At its next opposition in January 2025, Mars will only reach 14.6 arcseconds. 2022’s opposition won’t be beaten until 27 June 2033, when the planet’s apparent size increases to 22.1 arcseconds.
Photographing Mars
Widefield or close-up, there are many ways to capture the Red Planet
Imaging Mars can be as addictive as observing it. There are striking details to be resolved and, as December kicks off, we’re looking forward to widefield planetary imaging opportunities.
Look for a night with good seeing when the air is stable. You won’t need the kind of long exposures that nebulae require, so patchy clouds shouldn’t put you off. Because of the planet’s position relative to Orion and Taurus this month, it will form a beautiful orangey-red triangle with Aldebaran and Betelgeuse. Why not head out with your DSLR, wide-angle lens and a sturdy tripod to image this stunning arrangement? Set your exposure time to the longest you can achieve without star-trailing – for an approximate maximum exposure time divide 500 by the focal length of your lens or telescope. In terms of ISO, this will depend on the exposure time and camera model. Some will cope better than others at a high ISO. Start at 800 and work your way up.
Of course, opposition season really means we want to capture serious surface detail. For that you’ll need to dig out your tracking mount and longest-focal-length telescope. The good news is that DSLRs can still be used for planetary imaging as long as you can capture video, although preferably you would use a planetary camera as these capture higher frame rates, cutting through an unsteady atmosphere and giving a sharper image.
If using a DSLR, you will need a T-ring and adaptor that fits your telescope. You may still need a Barlow lens to enlarge your image, because Mars will still appear small. Given the tiny field of view of planetary cameras, it is often easier to locate the planet using an eyepiece, before popping the camera on. Due to the rotation of Mars, limiting videos to just a few minutes works best – say 2–4 minutes for a planetary camera or 3–5 minutes for a DSLR. There are free stacking and processing software programs, including AutoStakkert! and RegiStax, which will convert video files into a single image. If you’re looking to capture the lunar occultation, then take a look at our full guide.
Get a close look at the Martian surface
Now is the time to spy all the features visible on the Red Planet
Mars captures our imagination because it appears almost Earth-like with its polar caps, distinct surface details and occasional clouds swarming above. Its dusty composition, made up of iron and basalt, creates storms that cover the globe, obscuring its features for weeks. Meanwhile, Mars’s rotation and axial tilt of around 25° means that throughout opposition season we can look forward to a variety of different views as the surface appears to shift slowly eastward.
From 1 December, keep an eye out for the following disc features, tracking them up to and past opposition:
➤Polar ice caps Mars has seasons much like we do, which affect the size and shape of its polar caps. Sometimes its tilt means that only one is visible. However, for this opposition it might be possible to see both, depending on the seeing conditions.
➤Albedo features This is one for smaller scopes as well as more advanced setups. Albedo refers to how much light is reflected from a surface: light and dark areas. Mars’s dark patches are maria or seas, while the lighter areas are plains or continents, much like on our own planet.
➤The Hellas impact crater This massive, 2,300km-diameter circular basin – one of the largest in the Solar System – is located in Mars’s southern hemisphere. It will appear as a bright reddish-orange patch.
➤Syrtis Major This high plain of exposed volcanic rock is the largest dark area visible on Mars’s disc. Its V-shaped form should be obvious, but clouds can change the appearance of these darker surface areas, altering their colour or obscuring them.
Free programs such as Stellarium will help you plan your observing. Simply set the date and time and zoom in on Mars to find out which surface features could be visible throughout the night.
Opposition is a great time to track and record your Mars observations, either in sketches or images. Given the close approach, opposition and occultation all occurring within eight days, we’re viewing Mars in plenty of unusual circumstances. This also means that even if the weather isn’t always favourable, we can all hope to catch a great view of the Red Planet.
Charlotte Daniels is an astronomy journalist and experienced astrophotographer