Have you seen Mars yet? Watch for it tonight! You’ll find it easily because nothing else in the night sky resembles it now.
We’re now receiving emails daily from people wondering … what is that red star!? It’s not a star. It’s Mars. Since around July 7, Mars has been brighter than Jupiter, which is normally the second-brightest planet and fourth-brightest object in the sky after the sun, moon and planet Venus. Mars now outshines Jupiter by some 1.8 times. It’ll remain brighter than Jupiter until around September 7.
Remember Mars in 2003? That was the last time the red planet came exceptionally close to Earth. It was closer in 2003 than it had been in some 60,000 years. In 2018, Mars isn’t quite as bright as it was in 2003. But nearly!
Mars can be faint, or it can be a bright planet. Keep reading to learn why the appearance of Mars varies so widely in our sky, and why Mars is so bright now.
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 what make Mars a fascinating planet to watch with the eye alone. Mars was faint throughout 2017. If you saw it then and see it tonight, you won’t recognize Mars now!
So … 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 is only 4,219 miles (6,790 km) in diameter, making it only slightly more than half as big as Earth at 7,922 miles (12,750 km) in diameter.
The small size of Mars means that, when Mars is bright, its brightness isn’t due to its bigness, as is the case with Jupiter.
The main reason for Mars’ extremes in brightness has to do with its nearness (or lack of nearness) to 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 throughout most of 2017, Mars is far across the solar system from us.
Look at the diagrams below, which show Earth and Mars in their respective orbits around the sun …
Mars orbits the sun just one step outward from Earth’s orbit. 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. But 2018 is a very, very special year for Mars. Mars will appear brighter in our sky this year than it has since 2003.
The 2018 opposition of Mars isn’t an ordinary opposition, though. Astronomers call it a perihelic opposition (or perihelic apparition) of Mars.
In other words, we go between Mars and the sun – bringing Mars to opposition in our sky – around the same time Mars comes closest to the sun. The word perihelion refers 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 will be happening in 2018, and it’s why the Association of Lunar and Planetary Observers (ALPO) wrote:
The 2018 perihelic apparition of Mars will prove to be one of the most favorable since the 2003 apparition when the red planet came closest to Earth in 59,635 years (the year 57,617 B.C.).
Again, the Mars opposition is July 27, 2018. We will pass between the sun and Mars on September 16, 2018.
According to ALPO, in 2003 Mars came within 34.6 million miles (55.7 million km) of Earth, closer than at any time in over nearly 60,000 years! It’ll be only 1.2 million miles (just under 2 million km) farther away in 2018.
Closest approach for Mars in 2018 will take place on July 31, some four days after its July 27 opposition.
Bottom line: Mars alternates years in appearing bright and faint in our night sky. 2017 was one of the off-years, but, in 2018, we’ll have a grand view of Mars … best since 2003! July and August 2018 are the best months to see it.
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.