Mars is certainly one of the more interesting planets to view through a telescope. Being the only planet in the solar system with actual surface features you can see (Mercury is tiny and rarely easily viewed, and Venus has its obscuring clouds), as well as hosting dust storms and two moons, there is certainly a lot to look at. The allure of Mars and its Earth-like status and the possibility of hosting life has also attracted stargazers for centuries.
First, let’s go over some of the important things you need to view Mars with your telescope.
Mars Viewing Prerequisites
- #1: Wait for Opposition
Mars only gets closest to Earth once every 26 months. For a few months around either side of that date, it is big enough in the sky to easily view surface features. For the rest of the time, Mars appears rather small and it is far more difficult to discern any surface features. Mars and its moons also appear much brighter at opposition. The next opposition will occur in October 2020, with favorable enough conditions for viewing occurring between June-July 2020 and January or so of 2021.
- #2: Good Atmospheric Seeing
Atmospheric turbulence, or “seeing”, causes Mars and other small sky objects like the planets to appear shimmery or fuzzy in a telescope. This can be caused by a number of factors including:
- Looking over a surface that soaks up the heat in the daytime and releases it at night, such as pavement, concrete, or roofs
- Being located under the jet stream
- Natural atmospheric disturbances
Ideally, you should be looking over grass, water, rocks, or sand – not rooftops, chimneys, asphalt, or concrete. Observing near the ocean or over another body of water – if you can avoid sand and salt damage to your telescope – is optimal, as is observing from a hill or mountain top.
The lower Mars or any object is in the sky, the more atmospheric seeing will affect it. For best results, try to observe Mars when it is at its highest in the sky.
- #3: Aperture
The larger your telescope, the more angular resolution it has and the smaller the details you can see. Unlike light gathering ability which scales with the square of the aperture, the resolution is linear – so an 8” telescope will have twice the resolution of a 4” telescope.
However, once you get past about 10” or 12” or so, it is rare that you will ever have a night of seeing good enough to utilize the full resolution enabled by your telescope’s aperture, and thus it probably makes more sense to prioritize optical quality over aperture if you are able to afford a large telescope. This brings me to my next point…..
- #4: Good Optics
A telescope with poor optical quality or defects can make a huge difference in being able to view significant detail on Mars. Anything short of optimal will result in light scatter, smearing of the image, or a complete inability to focus at high power. Thankfully, unless you have bought a really low-quality telescope, this is usually not a problem.
A fast achromatic refractor will show severe chromatic aberration, blurring fine detail, and is thus not recommended for viewing Mars.
- #5: Telescope Collimation & Cooldown
A good telescope is of no use if the collimation is bad or it hasn’t cooled down.
If you own a Newtonian or Schmidt-Cassegrain, you should check your collimation before every observing session and make sure it is as perfect as you can get it before viewing Mars. If you’re unsure how to collimate or check collimation, read our guide. With refractors and Maksutov-Cassegrains, you shouldn’t have to worry much about collimation.
Cooldown affects all telescopes, though refractors suffer from the least cooldown issues. Even if the air temperature is only a few degrees lower than indoors, your scope’s objective lens or mirror will warp as a result of the temperature change and suffer from blurry images.
Newtonians can suffer from another thermal issue known as tube currents, where warm air hugs the tube walls for hours on end and distorts light before and after it hits your primary mirror. Tube currents are worsened by having a small tube only slightly larger than the mirror, particularly if it is made of metal – both of which are common on mass-produced Newtonians.
Typically, you should give your scope at least half an hour to cool down before attempting high-power viewing, and use cooling fans if possible – particularly on Newtonians. Some Newtonians such as the Zhumell Z series Dobsonians come with cooling fans, and some vendors sell them to easily attach to your telescope. You can also make your own using 12-volt DC powered computer fans and a battery pack, with minimal electronics knowledge or soldering required. Propping an ordinary house fan behind your primary mirror will also work in a pinch. Just remember to turn the fan off before actually doing any viewing!
- #6: Good Eyepieces
Low-quality eyepieces and Barlow lenses may cause scatter, chromatic aberration, and other defects which can make it hard to view fine details on Mars and more easily hide its moons within the planet’s glare. So try to get yourself some decent eyepieces. They don’t need to be wide-field necessarily, just free of scattering and chromatic aberration.
Tips on Observing Mars
- What to Look For
Mars displays three main types of features: Albedo markings, polar caps, and dust storms.
Albedo markings are dark areas on Mars where the wind has swept away dust and revealed dark rocks underneath. They can change in exact size and shape as a result, and were once thought to be massive patches of vegetation. Most telescopes will show around four at any one time, with up to maybe ten visible total to a typical untrained eye. With practice, you may be able to count up to twenty or so.
Some of the Martian albedo features do in fact correspond to topographical features, such as the Aurorae Sinus region which is, in fact, part of the massive canyon Valles Marineris, Nix Olympica which corresponds to Olympus Mons – the largest volcano in the solar system -, and of course Hellas Planitia, a giant ancient crater. However, most of the larger and thus more easily observed albedo regions are just patches of dark terrain.
Mars’ polar caps are pretty self-explanatory – frozen deposits of water and carbon dioxide ice at the poles. Because Mars has an axial tilt very much like Earth, you will usually only easily see one at any one time, with the other at least partially if not fully shrouded in darkness on the non-observable side of Mars. The polar caps are undoubtedly the easiest Martian feature to observe, and almost any telescope will show them with at least 50x magnification or so around the opposition.
Lastly, dust storms. Martian dust storms can vary widely from small orange-yellow patches to global storms that all-but-obscure even the most prominent albedo features and the ice caps. They usually happen during Mars’ northern hemispheric summer – which also corresponds to when Mars is closest to the Sun, thanks to its rather elliptical orbit. The extra heat stimulates Mars’ wind and the low gravity and atmospheric pressure easily results in planet-wide dust coverage.
In general, assuming good seeing, I recommend using around 30-40x per inch of the aperture when viewing Mars. Most of the Martian features are relatively low-contrast and bringing up the magnification too much only smears them and makes them less defined. At the same time, too-low magnification will result in Mars appearing so bright that it’s hard to see anything.
Some observers recommend using various filters to bring up the contrast, or a neutral-density filter to bring down Mars’ brightness.
I don’t have much experience in using colored filters on Mars, but a red or orange filter seems to produce the best results. If you really need a neutral density filter to dim Mars, the magnification you are using is probably too low.
Viewing Phobos & Deimos
Both Phobos and Deimos are rather dim and really require at least an 8” telescope to see.
Phobos orbits extremely close to Mars – so close, in fact, that it is only really observable when Mars is very close to the opposition. Even then, you’ll need to wait for it to be at an optimal elongation from the planet – which, thankfully, occurs at least twice a night thanks to Phobos’ 7 hour, 40-minute orbital period. Even then, you’ll need to put a strip of tape or a similar occulting bar-like device across the center of your eyepiece’s field lens to block out Mars itself to shield Phobos from its glare at least partially.
I have seen Phobos once. Very few people have at all. It is very, very challenging to do.
Deimos is much easier. I have spotted it with a 6” telescope, albeit with difficulty. It is quite easy with a 10” or 12”. With a typical high-magnification eyepiece you should be able to see Deimos simply by placing Mars outside the field of view in the right direction.