Mars Makes A Move On Its Rival Antares

A dawn planetary surprise — the planet Mars in the head of Scorpius shines a little more than 0.5° from the 2nd magnitude double star, Graffias, on Jan. 8, 2020. Bob King

I like to think I know my way around the sky, but the other morning I was lost. Just for a moment. I had to get up early to speak at an event. Fortunately, the sky was clear so I took in a 360 of the spring stars while loading the car in the subzero cold. Orion had departed. In his place were Lyra the harp, Hercules the strongman and Boötes the herdsman. Arcturus gleamed high in the southern sky, exactly where it will be on sultry May evenings. I’ve always loved the sight of the dawn stars as a forecast of what’s to come.

But when my gaze dropped into the southeastern sky I saw a close pair of stars I didn’t recognize. My first thought was Alzheimer’s (no kidding), but then it hit me — that’s Mars! Planets always mess with constellation patterns, and if you don’t routinely follow their movements, they will trip you up. Of course, I hadn’t paid any attention to Mars for a few weeks because I’m not usually up at 6:30 a.m. so it got away from me.

Watch Mars slide past similarly bright (and colorful!) Antares in the constellation Scorpius in the next week. The crescent moon joins the scene on Jan. 20 and 21. The animation spans from Jan. 13-21. Stellarium

Planets are constantly on the move because they orbit the sun. Mars comes closest to our planet than any other except Venus, so it chugs across the sky relatively quickly. Right now, it’s scooting along at more than one full moon diameter each day, making its morning-to-morning movement super easy to track with the naked eye.

Earth and Mars are closing in on each other with ours the faster planet. When Earth laps Mars at opposition on October 13 the two will be their closest until 2035, and the Red Planet will shine as brightly as Jupiter. Right now, it’s only magnitude 1.5 (about as bright as Betelgeuse in Orion) and a little fainter than Antares. Antares is a bright, red supergiant star that marks the “heart” of Scorpius.  The name comes from Anti + Ares (the Greek names for Mars) and means “rival” or “opponent” of Mars because they have a similar brightness and color. Why they can’t just be friends, right? It’s so characteristically human to transfer our emotions to the sky.


Antares shines with a strong red tint. It’s a huge and comparatively cool red supergiant star in the late stages of its life on the way to becoming a supernova. Astronomers recently mapped the star’s surface to show heat bubbles rising up from below. ESO

Antares is about 550 light years from Earth and one of the largest naked eye stars visible to the naked eye with a diameter equal to 3.4 times Earth distance from the sun. Oh, and it’s 60,000 times brighter, too. Mars on the other hand is a rather small ball of rock 4,200 miles (6,760 km) wide. Yet they’re so similar in outward appearance despite their great differences. Nature … always the joker.

You can watch Mars glide right past Antares in the coming week, passing closest (4.5°) on Jan. 17-18. Look low in the southeastern sky about 90 minutes to an hour before sunrise. Compare their color and brightness. Antares has the edge in brightness but not for long. Mars will equal its rival in early March and then surpass it as the distance between the two planets shrinks.

On Jan. 20th watch for the thin lunar crescent to put in an appearance. If you pay attention to Mars this month you’ll get a real sense of the planet moving along its orbit. In the northern hemisphere, planets move east across the sky as they orbit the sun. If you ignore Mars don’t be surprised if one morning you look and wonder why there are two bright “stars” together at dawn.

I told you so.