How to See Mars in a Telescope

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If you are reading this because you are about to buy a telescope to look at Mars, start with the calendar rather than the catalogue. Mars is the one planet where the date on which you observe matters more than the money you spend: the same telescope, pointed at Mars in a good year and a bad one, delivers two experiences so different that people assume the instrument has failed. It has not. Earth and Mars simply drift between roughly 56 and 400 million kilometres apart, and the planet’s apparent size rises and falls with them.

So this guide is organised around timing. Get the timing right and a modest telescope shows you a small ochre world with a white cap and grey markings. Get it wrong and a large telescope shows you an orange spark.

Why Mars is an all-or-nothing target

Mars orbits outside Earth, but not far outside, and its orbit is noticeably lopsided. Earth catches up and passes it roughly every 26 months — that pass is opposition, and it is the only time Mars is worth serious telescope time. Away from opposition, Earth and Mars can be more than five times further apart, and the planet shrinks to a dot.

Worse, not all oppositions are equal. If we pass Mars when Mars is near its closest point to the Sun (perihelic), it can loom large and brilliant. If we pass it when Mars is near its most distant point (aphelic), the same opposition delivers a disk barely half the area. The cycle runs roughly fifteen to seventeen years from one run of great oppositions to the next.

Opposition dates are listed in the astronomy events calendar, with the good ones flagged.

What Mars shows you, by where you are in the cycle

Aperture matters for Mars, but it is the second variable. Here is the same telescope — call it a 150mm reflector, the size at which Mars starts to behave — across the cycle.

Six months either side of opposition. Mars is a small orange dot: bright to the eye, blank in the eyepiece, under 8 arcseconds. You can confirm it is a disk rather than a point and that is the whole observation. No telescope of any size rescues this period, and this is when most disappointed reviews of telescopes get written.

The two months around an aphelic opposition. A definite disk with a white polar cap, and on a calm night the largest dark region — Syrtis Major, the dusky wedge that Christiaan Huygens used to time Mars’s rotation in 1659 — drifting into view. This is a real, satisfying observation that rewards patience and punishes impatience, and it is what the rest of the 2020s offers.

The two months around a perihelic opposition. The same telescope now shows several distinct dark regions, a cap that visibly shrinks from week to week as the Martian spring advances, occasional bright cloud at the limb, and the disk large enough that a sketch takes real effort to finish. This is what people mean when they talk about seeing Mars.

Smaller and larger instruments scale from that: 60–70mm gives you a tiny salmon disk and, at a strong opposition, a hint of the cap; 100–130mm makes the cap plain and Syrtis Major reachable; 250mm and up delivers genuine surface geography on the few nights each year when the air cooperates. Binoculars, at any opposition, show an orange star and nothing else, ever.

Two further complications. Mars rotates in 24 hours 37 minutes, so the face presented at 10pm tonight is almost the same face at 10pm tomorrow, drifting slowly over weeks — you have to observe across a month to see the whole planet. And Mars produces global dust storms that can wipe every marking off the disk for weeks. That has happened at a major opposition before, to widespread collective dismay.

How to find it

Mars is the easiest planet to identify by colour: a distinctly orange “star” that no amount of staring turns yellow or white. Near a good opposition it outshines everything except Venus and Jupiter, and the colour carries to the naked eye from a city street. Away from opposition it is an unremarkable orange dot, easily confused with the star Antares — whose name means “rival of Mars”, which tells you how old that confusion is. If you want to settle it, check whether it has moved against the background stars a week later; Antares will not have.

For the constellation it is sitting in, use the events calendar or a sky app, then match the pattern overhead. A paper planisphere is the fastest way to learn those patterns and the only piece of kit here that never needs charging; we compare versions in best planisphere, and there is a full finding routine in how to see Saturn’s rings that works just as well for Mars.

Magnification, seeing and patience

Mars demands more magnification than the other planets precisely because it is small: 180x to 250x if the air will take it. That is also why Mars punishes a poor telescope so severely. At 250x every defect shows — a wobbly mount, a tube that has not cooled, a reflector out of collimation, turbulent air.

Practical rules that actually help:

• Cool the telescope for a full 45 minutes. Non-negotiable for Mars. A tube still shedding indoor heat generates turbulence inside itself, and at 250x that turbulence is all you will see. Thirty minutes is the minimum that changes anything; forty-five is the number to plan around.
• Observe when Mars is highest, not when it is convenient.
• Stay at the eyepiece for fifteen minutes. Markings on Mars appear in split-second moments of steady air. People who glance and leave see an orange blob and conclude there is nothing there.
• Try slightly less magnification than feels right. A small sharp disk shows more than a large soft one.
• Observe repeatedly across the opposition month. Different faces, different air, different results.

Mars is also the one planet where a colour filter earns its keep. A light yellow or orange filter lifts the contrast of the dark markings against the ochre background, and a light blue one picks out limb clouds and hazes. The effect is modest and it needs aperture: from about 150mm upwards there is something to gain, while in a 70mm tube a filter mostly makes a dim image dimmer. If that is where you are, a colour filter set is worth the curiosity — as a small gain on a good night, not as a cure for a disappointing view. For Jupiter and Saturn the same filters do close to nothing, which is why we tell people not to bother there.

What equipment is actually worth it

Mars is an aperture planet. Everything below follows from that.

• 150mm of aperture, on a mount that stays put: a 6-inch Dobsonian. The Sky-Watcher Classic 150P is the sensible floor for Mars — enough light grasp to hold 200x, a base that absorbs the shakes a Mars night will otherwise amplify, and still liftable in one piece. Where it sits against the rest of the bracket: best telescope under $500.
• Or 200mm, if you have the space and will use it on everything else too. The Sky-Watcher Classic 200P is the step that makes dark markings and limb cloud routine rather than occasional at a decent opposition. It is heavier, taller and needs somewhere to live; buy it for the whole sky, not for one planet. Comparisons in best Dobsonian telescope.
• A short eyepiece or a Barlow to reach 180x–250x — a 6mm, or a 9mm plus a 2x Barlow. See eyepieces for beginners.
• A collimation tool if you own a reflector. At 250x a mirror a fraction out of alignment costs you the whole observation, and a Cheshire eyepiece settles it in two minutes with no batteries and nothing to go wrong. Methods in collimation tools.
• A red flashlight for charts and sketching — and sketching is how you will notice the cap shrinking. Choices in best red headlamp; the wider buying order is in accessories to buy first.
• Not a bigger telescope bought in a hurry two weeks before an aphelic opposition. Wait for a good one: the gap between a poor opposition and a great one is far larger than the gap between a 150mm and a 250mm telescope.

Can you see the moons of Mars?

Phobos and Deimos are tiny and sit deep in the planet’s glare. They are a real challenge object for large amateur telescopes at the best oppositions, using an occulting bar to hide Mars itself. For almost everyone reading this, the answer is no.

Three questions that decide a Mars night

Is this opposition a good one?

Check before anything else. A perihelic opposition puts a 22–25 arcsecond disk in front of you; an aphelic one gives 13–15, which is less than half the area. The current run is the unfavourable kind and conditions improve markedly in the early-to-mid 2030s. Dates are in the events calendar.

Is the telescope ready, and am I?

Cooled for 45 minutes, collimated if it is a reflector, and pointed at Mars when Mars is high rather than when you happen to be free. Then fifteen minutes at the eyepiece before you form an opinion. Those four things separate people who see the polar cap and Syrtis Major from people who see an orange smudge with the same equipment on the same night.

Should I buy a telescope for Mars at all?

Only with your eyes open. If Mars is the sole reason, check the opposition first — and weigh up that Jupiter and Saturn deliver every year, which makes them a far safer reason to spend money. Around 100mm will show the polar cap at a reasonable opposition; 150mm makes it comfortable; and see best telescope for beginners if this is your first.

Keep reading

• Astronomy Events Calendar — the page to check before you spend anything on Mars.
• How to See Jupiter and Its Moons — the planet that never makes you wait for a good year.
• How to See Saturn’s Rings.
• Best Dobsonian Telescope — the most aperture per dollar, which is the whole Mars argument.
• Best Collimation Tools — because at 250x this stops being optional.