How to See Mars Through a Telescope – Updated for 2021

When it is nearby, seeing Mars through a telescope is a spectacular sight. When it is at its farthest, the view is much less inspiring.

Although it’s our neighbor in space, the distance between Mars and Earth fluctuates massively over a two-year period. At their closest, they can be just 35,000,000 miles (56 million km) apart. When they are on opposite sides of their respective orbits, Mars can be 250,000,000 miles (401 million km) apart.

Showing all sides of Mars near its 2020 opposition
Mars at close approach (click for full-screen). Courtesy Chilescope / Damian Peach

You won’t be surprised to learn that the view you’ll get of Mars in your telescope when it’s 7x closer to us is spectacular compared to when it is at its most distant.

At its closest, the disc can be 25 arcseconds in diameter, at its furthest, it can be just 3.5″ across, smaller than Uranus in your telescope. This has a significant impact on the planet’s apparent magnitude too, which can be as dim as +2.0, or as bright as -3.0.

Series of Mars images as it approaches opposition in 2020
Mars ‘growing’ as opposition approaches (click for full-screen). Courtesy Luis Amiama.

Suffice to say, you need to pick your moment to look at Mars. As the image above shows, much of the time it is a tiny, uninspiring red dot. When it is nearby, however, it is a large disc, rich in features to be discovered.

Read on to find out when you should be looking for the red planet, and what to look for when you’ve found it.

When Is Mars Visible?

2020 was a great year for seeing Mars. In October of last year, it came as close to Earth as it has for more than eight years. We saw the Martian disc reach 22 arcseconds wide, and it shone at magnitude -2.6.

Unfortunately, this means that 2021 is a fallow year for Mars. There is no opposition to be enjoyed and the planet spends the first half of the year getting smaller and fainter as it moves closer to the Sun.

This means its surface features and its moons, Phobos and Deimos, are practically impossible to see without a large telescope.

The story gets no better as 2021 progresses: Mars gets too close to the Sun to be seen from around July. It reaches conjunction on 08 October, when it will be directly behind the Sun from our perspective, and does not appear in dark skies again until the very last days of the year.

However, outside of the conjunction period, Mars is visible in our night skies. The table below shows the rise and set times for the red planet at mid-month for the year. The third column shows what time it will be at its highest.

Note that the planet rises in the morning and is in the sky only during daylight hours from September to November.

Rise, culmination, and set times for Mars in the middle of each month in 2021.
Rise and set times for Mars in 2021 (data source)

Although this chart is set for a mid-US timezone, the times will be approximately the same for local timezones in most of the northern hemisphere.

When Is Mars at its Brightest?

The chart below shows how the brightness (magnitude) of Mars varies throughout 2021.

You can see that the planet is brightest (the lowest magnitude) at the beginning of the year. As winter gives way to spring, the magnitude falls from 0.1 to 1.8, which is where it will stay until a slight improvement in brightness towards the end of the year.

Chart showing the magnitude change in Mars over the course of 2021
The magnitude of Mars in 2021 (click for larger version). Data from in-the-sky.org.

The decrease in brightness throughout the year is a result of Mars moving farther and farther away from us. The chart below shows how far away Mars is from Earth for each month this year.

You’ll see that it is furthest from us as it goes around the Sun in early October before slowly moving back towards us again.

Chart showing the distance of Mars from Earth in astronomical unit (A.U.) each month in 2021.
Distance of Mars in 2021 (click for larger version). Data from in-the-sky.org.

Finally, let’s take a look at how big Mars is in our sky this year.

As you might already expect, it appears larger at the beginning of 2021 when it is closest to us. Conversely, it is at its smallest when it’s furthest from us in early fall.

The chart below shows the size of its diameter in the middle of each month, measured in arcseconds.

Chart showing the apparent diameter of Mars, measured in arcseconds, over the course of 2021.
Diameter of Mars in 2021 (click for larger version). Data from in-the-sky.org.

In January, Mars is more than two-and-a-half times the size it will be late summer/early fall. That’s why we’ll get the best views when we look earlier in the year.

If you’re planning to find our neighbor with your telescope, keep reading to see how to do it.

How to Find Mars In A Telescope

It might not be at its best this year, but the earlier you look, the larger and brighter the Martian disc will appear.

Here’s our guide to getting the best of Mars in 2021.

Step 1: Is Mars in the Sky Tonight?

As mentioned above, Mars is best viewed in the evenings in the first half of 2021, and the earlier in the year you look, the better it will appear.

The screengrab below from SkySafari 6 shows the path of Mars against the background stars this year. Remember, there is no Sun shown on this image and, in reality, Mars will be too close to our star to be viewed from late July until late December.

Click here to see our complete month-by-month guide to seeing Mars in 2021.

The path of Mars against background stars from Jan to July 2021
The path of Mars to July 2021 (click for full-screen)

When Mars re-emerges from behind the Sun in December 2021, we’ll find it in the constellation of Ophiuchus an hour before sunrise. Its disc will be tiny – about the same as that of Uranus – and it’ll be shining at magnitude 1.5.

Step 2: Finding Mars Without a Telescope

In the earliest weeks of the year, Mars is still relatively bright and easy to spot in the evening sky. As shown in the diagram above, you can find it in Pisces in January, then Aries, Taurus, and Gemini as the months progress.

In January see it best around 8 pm. From March until we lose it July, Mars is best viewed as soon as it gets dark after sunset.

As the ‘Red Planet’ name for Mars suggests, what makes this planet easy to pick out against the stars is it shines with an obvious red hue. It will also be brighter than almost all of the stars nearby.

Step 3: Finding Mars With a Small Telescope

Make sure that your telescope is ready to go, i.e. you have aligned the finderscope. If you don’t have a telescope yet, these are our top picks for telescopes to see Mars.

Aim your finderscope at the red ‘star’ you picked out above and take a look through a wide field of view eyepiece.

While actual stars will remain as pinpricks of bright light, Mars will appear as a distinct disc, albeit a shrinking one as 2021 ages.

Mars is still relatively bright, so don’t be shy to use larger magnifications to see what you can observe on its surface. However, keep in mind that this year is not great for seeing details of the Martian surface.

Step 4: Improving Your View With a Telescope Filter for Mars

To observe more details on the Martian surface, it helps to use a telescope filter to enhance surface contrast and reveal more features that you might otherwise miss.

Discover the best telescope filter for each planet in our handy table

Filters remove unwanted light from your view, leaving useful colors behind. With fewer colors reaching your eyes, your brain is much better at interpreting the differences it sees, so you can tease out different features on the Martian surface.

These are the most useful filters for observing Mars. Click the filter number to buy one (or just check the price) on Amazon, which will open in a new tab.

#21 Orange – Enhances darker surface areas against the general bright orange background of the planet.

#23A Light Red – Highlights the planes and does a good job too with dust storms and the polar ice caps. If you were to choose just one filter for observing Mars, this should be it.

#56 Light Green – A good choice for dust storms and ice cap viewing.

#82A Light Blue – It’s hard to imagine blue improving the Red Planet’s view in a telescope, but it darkens the rust-colored disc and shows off the polar ice caps.

What Can You See on Mars With a Small Telescope?

When Mars is large and presenting good viewing, it is the best planet for detailed surface feature observations. Its surface is varied enough to show deserts, differently shaded landscapes, polar ice caps, and even clouds and dust storms.

The image below gives a map of what was visible on the Martian surface at its last big opposition in October 2020. Click the image for a full-screen version.

Map of Mars taken at opposition in October 2020
Map of Mars (click for full-screen). Courtesy Luis Amiama

Keep in mind that the features mapped above were caught with a camera through an 8″ telescope at opposition, so we can rarely see this level of detail. Even if you have the scope and conditions, our eyes never reveal as much as a camera can.

If you have a smaller scope than that, what can you expect to see when Mars is at its closest?

Thankfully, Mars delivers even for a small telescope… when it is nearby. The best feature to see is the southern polar ice cap, which is pointed towards us at opposition. Its white stands out against the rust. Even a 3-inch to 4-inch scope will reveal it.

The other surface features rely on being able to distinguish differences between light and dark areas of the surface. Depending on which side of the planet is facing us when you look, try and see Syrtis Major or Mare Acidalium, More details on both, below.

Finally, you can also see dust storms through a small telescope but we’d rather not because that means better surface features are being obscured.

Target 1: How to See Polar Ice Caps on Mars

Even though Mars has almost no atmosphere, the top and bottom of the planet both experience the growth of polar ice caps during the respective northern and southern winters. We can see these using a small telescope, especially when Mars is closer.

The southern cap tends to be most obvious when Mars is at opposition (closest to us). Have the patience to wait for moments of good seeing and note the distinct white ice caps against the red of the planet.

Shows the Martian southern polar ice cap large in July 2018 and shrunk in October 2020.
Mars southern ice cap, large in 2018, small in 2020 (click for full-screen). Courtesy Mailliard.

As the image above perfectly demonstrates, the size of the ice caps is subject to seasonal variations on Mars. When the southern hemisphere is experiencing its winter, the ice cap is much larger, as shown in the left image. This makes it much easier to see in a planetary telescope.

Target 2: Martian Surface Features

The Martian surface has Valles Marineris, a valley deeper and longer than the Grand Canyon, and the tallest volcano in the solar system – Olympus Mons. However, a smaller telescope will not reveal these to us directly. Instead, we need to hunt for larger features that are more obvious.

Discover more about Mars: What is Mars Made Of, And Why Is It Red?

You may already know that the Moon has mares, which are the darker ‘seas’ visible on its surface. Well, the Martian surface has these too.

There are two of these darker areas which are large and distinct enough to be seen with a small telescope: Syrtis Major and Mare Acidalium.

Syrtis Major is a roughly triangular area of darkness pointing towards the north pole. On the other side of the planet, Mare Acidalium is a dark region in the north of the planet which extends southwards.

Use a Martian map, like this one, as your guide to see what else you can discover.

Target 3: Dust Storms

By their nature, Martian dust storms are unpredictable.

They tend to be massive and can be picked up in a telescope when the planet is nearby. Sometimes, on average every five years, the whole planet becomes enshrouded in sand.

Our advice is to keep up with discussions on Cloudy Nights’ solar system observing forum. This is where conversations about Martian dust storms will be had as soon as they happen.

Got a Larger Telescope? See Our Guide to Major Surface Features on Mars

Summary

Mars is iconic.

Its red body is a sight all astronomers want to see and explore with their telescopes.

Enigmatically, it only reveals itself fully to us for three or four months every two years. And, sadly, 2021 is not one of them.

However, it pays to be ready to observe Mars when it is back to its magnificent best, so practice seeing it now, even though it’s distant. This will be the perfect preparation for the thrill of seeing it up close, when it next reaches opposition in December 2022.


Written by Adam Kirk