Now is the time to start watching Mars

Mars has been inconspicuous in our predawn sky for some months. It’s slowly gotten brighter and redder. Now the drama is about to begin! By October, Mars will outshine Jupiter! Start watching it now, and enjoy the fun.

Several small white dots on black background with one big glowing red dot labeled Mars.

Dennis Chabot of POSNE NightSky captured this photo of Mars on July 21, 2018. Mars was very bright and very red for several months around then! And it’ll be very bright and very red again … soon.

In the year 2018, Mars was brighter than all the stars. It was even brighter than the second-brightest planet, Jupiter. It was a blazing red dot of flame in our night sky for several months. In 2019, Mars was mostly faint. It was barely noticeable in our sky. Why? Why is Mars bright in some years, but faint in others? And why is Mars expected to brighten dramatically again in 2020? Keep reading to learn why the appearance of Mars varies so widely in our sky, making Mars one of the most interesting planets to watch!

June 2020 is a wonderful time to start watching Mars. It’s in our predawn sky now, but will soon be visible late at night … and then at sunset. See the chart below to learn to find Mars this week. Want to see Mars in the coming months? Bookmark EarthSky’s planet guide.

Chart: moon's positions on 3 days, Mars, location of Neptune, and star Fomalhaut.

At mid-northern latitudes, you’ll have to get up mighty early to catch the moon and the red planet Mars in the predawn sky in June 2020. Read more.

More than any other bright planet, the appearance of Mars in our night sky changes from year to year. Its dramatic swings in brightness are part of the reason the early stargazers named Mars for their god of war; sometimes, the war god rests, and sometimes he grows fierce! Mars was faint throughout 2017, bright in 2018, and was faint again for most of 2019. Right now – in June 2020 – Mars is brighter than it was a few months ago, growing noticeably redder.

Why? Why does Mars sometimes appear very bright, and sometimes very faint?

The first thing to realize is that Mars isn’t a very big world. It’s only 4,219 miles (6,790 km) in diameter, making it only slightly more than half Earth’s size (7,922 miles or 12,750 km in diameter).

The small size of Mars is your first clue to its varying brightness. The small size means that, when Mars is bright, its brightness isn’t due to bigness, as is the case with the largest planet in our solar system, Jupiter.

Double photo with large Earth on left and smaller Mars on right, to scale.

Mars isn’t very big, so its brightness – when it is bright – isn’t due to its bigness, as is true of Jupiter. Mars’ brightness, or lack of brightness, is all about how close it is to us. Image via Lunar and Planetary Institute.

Long exposure with big dot of Mars and its reflection in a lake, and Milky Way soaring above.

Matt Pollack captured Mars from Little Tupper Lake in the Adirondacks of upstate New York in July 2018. Read more about this photo.

Instead, the main reason for Mars’ extremes in brightness has to do with its nearness (or lack of nearness) to Earth.

Mars orbits the sun one step outward from Earth. The distances between Earth and Mars change as both worlds orbit around the sun. Sometimes Earth and Mars are on the same side of the solar system, and hence near one another. At other times, as it was for much of 2017 and was again for much of 2019, Mars was moving on the opposite side of the solar system from Earth.

Look at the diagrams below, which show Earth and Mars in their respective orbits around the sun in mid-2018 and this month, June 2020 … and then in October 2020, when Earth and Mars will be closest for this two-year period.

Chart: concentric circles of planetary orbits with positions of planets, Earth and Mars very close.

Earth (blue) last passed between between the sun and Mars (red) on July 27, 2018. This was Mars’ opposition. It comes to opposition about every 2 years, and, at such times, Mars is always at its best for that 2-year period. There’s also a 15-year cycle of Mars, whereby the red planet is brighter and fainter at opposition. In July 2018, we were at the peak of the 2-year cycle – and the peak of the 15-year cycle – and Mars was very, very bright! Image via Fourmilab.

Concentric circular orbits showing relative position of planets in the inner solar system around June 11, 2020.

Mars passed most directly behind the sun from Earth in September 2019, and, for many months, the planet has been far across the solar system from Earth. But now Earth (blue) is beginning to catch up to Mars (red). This chart shows June 2020. See the chart below. Image via Fourmilab.

Large heliocentric chart showing concentric planetary orbits with positions of planets October 13, 2020.

This chart shows the relative positions of Earth (blue) and Mars (red) at the time of Mars’ coming opposition on October 13, 2020. Around that time, Mars will appear bright in our sky again – and in the sky all night long – but it won’t be as bright as it was in 2018. Image via Fourmilab.

Earth takes a year to orbit the sun once. Mars takes about two years to orbit once. Opposition for Mars – when Earth passes between Mars and the sun – happens every two years and 50 days.

So Mars’ brightness waxes and wanes in our sky about every two years. Because of this, 2018 was a very, very special year for Mars, when the planet was brighter than it had been since 2003. Astronomers called it a perihelic opposition (or perihelic apparition) of Mars. In other words, in 2018, we went between Mars and the sun – bringing Mars to opposition in our sky – around the same time Mars came closest to the sun. The word perihelion refers to Mars’ closest point to the sun in orbit.

Maybe you can see that – in years when we pass between Mars and the sun, when Mars is also closest to the sun – Earth and Mars are closest. That’s what happened in 2018.

2003 was the previous perihelic opposition for Mars. The red planet came within 34.6 million miles (55.7 million km) of Earth, closer than at any time in over nearly 60,000 years! That was really something.

Earth's and Mars' orbit with Mars in different sizes at different points around its orbit.

Diagram by Roy L. Bishop. Copyright Royal Astronomical Society of Canada. Used with permission. Visit the RASC estore to purchase the Observer’s Handbook, a necessary tool for all skywatchers. Read more about this image.

And now? Earth will pass between Mars and the sun next on October 13, 2020. The red planet will appear brightest in our sky – very bright indeed and fiery red – around that time.

And thus Mars alternates years in being bright in our sky, or faint. 2019 was a dull year, but 2020 will be an exciting one, for Mars!

Now is the time to start watching Mars. When you spot it, keep your eye on its, and enjoy its growing brightness. And think what’s causing the brightness change: our own Earth, rushing along in our smaller, faster orbit, trying to catch up.

Watch for Mars!

Sun, Earth, Mars lined up with orbits shown.

Artist’s concept of Earth (3rd planet from the sun) passing between the sun and Mars (4th planet from the sun). Not to scale. This is Mars’ opposition, when it appears opposite the sun in our sky. Image via NASA.

Bottom line: Mars alternates years in appearing bright and faint in our night sky. In 2018, we had a grand view of Mars … best since 2003! In 2019, we were in one of Mars’ faint years. But 2020 will – once again – be a bright year for Mars. June 2020 is a great time to notice Mars so that you can watch it get brighter in the coming months.

Photos of bright Mars in 2018, from the EarthSky community

Deborah Byrd