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. And now Mars is bright again, brighter than all the stars. It’s not as bright as Jupiter yet, but it soon will be, for about a month surrounding mid-October 2020. Why? Why is Mars bright in some years, but faint in others? And why is Mars brightening so dramatically again now? Keep reading to learn why the appearance of Mars varies so widely in our sky, making it one of the most interesting planets to watch! Most importantly, learn how to start watching Mars now, so you can enjoy it for the remainder of this year.
September 2020 is a wonderful time to start watching Mars. It’s rising in the east now not long after the sun goes down. You can’t fail to recognize Mars. It’s very bright, and it’s very red in color.
As the weeks go by, Mars will be rising earlier. By mid-October, it’ll be rising in the east as the sun sets in the west. After that, for the remainder of this year, Mars will be in our sky at sunset, fading in brightness as the year draws to a close, but still … a sight to see. To learn how to find Mars in the coming months, bookmark EarthSky’s planet guide.
So – 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!
To understand why Mars varies so much in brightness in Earth’s sky, first realize 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).
Consider Mars in contrast to Jupiter, the biggest planet in our solar system. Jupiter always looks bright, because it’s so big.
Not so for little Mars. Its extremes in brightness have 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 was the case for much of 2019, Mars moves on the opposite side of the solar system from Earth.
Look at the diagram below, which shows Earth and Mars in their respective positions in their orbits around the sun in October 2020, when Earth and Mars will be closest for this two-year period.
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.
And now? Earth will pass between Mars and the sun next on October 13, 2020. The red planet is now bright and fiery red and will be for weeks to come.
Now is the time to start watching Mars. When you spot it, keep your eye on its, and enjoy its 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!
Bottom line: Mars alternates years in appearing bright and faint in our night sky. In 2018, our view of Mars was the best since 2003! In 2019, we were in one of Mars’ faint years. But 2020 has brought another bright year for Mars. If you start watching Mars in September 2020, you can see it at its best and enjoy it for the remaining months of this year.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.