Remember Mars in 2003? That was the year the red planet came closer to Earth than it had been in some 60,000 years. Mars can be a bright planet. It can outshine most stars. But, in 2003, for a few months, Mars was exceedingly spectacular in our sky, outshining all the stars and planets except brilliant Venus. In 2018, Mars won’t be quite as bright as it was in 2003. But nearly!
It’ll dramatically brighten over the coming months to appear as a red dot of brilliant flame in our sky around July, 2018.
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. But it’s brighter now, as you might notice if you’ve been watching the planet in the predawn sky. Mars was very close to Saturn in early April (see photos), and it’s still near Saturn (though not as close) as you can see from the chart above. Jupiter is up before dawn now, too, and, when you contrast the brightness of Jupiter and Mars in April 2018, you might not believe that Mars will be brighter than Jupiter this July.
But it’s true. In late July 2018, around the time Earth sweeps between Mars and the sun, Mars will outshine Jupiter by some 1.8 times.
And that will be something to see!
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. So, when it’s 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 the proximity (or lack of proximity) of Earth and Mars during the orbits of both worlds around the sun. It’s about the nearness in space of our two worlds. 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.
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.
This 2018 opposition of Mars isn’t an ordinary opposition. Astronomers will call it a perihelic opposition (or perihelic apparition) of Mars. The word perihelion refers the point in Mars’ orbit when it is closest to the sun. 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.).
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.
For a period of about two months, Mars will supplant Jupiter as the fourth brightest celestial body, after the sun, moon and Venus. Mars’ reign as the fourth-brightest celestial body (or third brightest in the nighttime sky, after the moon and Venus) will last from about July 7 to September 7.
So 2017 was, indeed, a lousy year for Mars. But just wait! Mars will be grand in 2018.
How can you find Mars throughout this year? Check out EarthSky’s monthly planet guide.
Bottom line: Mars is bright when it and Earth are on the same side of the sun. It’s faint when it and Earth are on opposite sides of the sun. 2017 was one of the off-years, and Mars was faint in our sky throughout last year. But, in 2018, we’ll have a grand view of Mars … best since 2003!
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.