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Mars and "Not Mars"


(Credit: Stellarium)

Looking for Mars in the sky? Don’t mistake it for its rival.

You’d think the planet Mars would be easy to identify because it looks reddish. But there’s a problem: some stars are reddish, too. And this summer, Mars lies in the early evening southern sky in roughly the same direction as one of those stars, the red supergiant Antares.               

Antares is aptly named. Ares and Mars were the Greek and Roman gods of war, respectively. So the name Antares can be translated as the rival of Mars. Think “anti-Ares” or “not Mars.”

You can imagine Antares to be the red heart of Scorpius the Scorpion. But you don’t need to know how to identify the constellation Scorpius to tell the difference between Mars and Antares.

Just notice which one twinkles. Then recall how the nursery rhyme goes: “twinkle, twinkle, little star.” Not “twinkle, twinkle, little planet.” Antares, being a star, twinkles. But Mars, being a planet, usually shines more steadily.

The apparent size of a star vs. a planet helps explain why stars twinkle but planets generally don’t. Even though Antares is actually very, very large (even larger than our own Sun, by a lot), it’s so very far away from us that it appears as a mere pinpoint of light in the sky, even if you look at it through a telescope. This is also true of the other stars in the night sky.

But being in our own solar system and thus relatively close to us, Mars—even though it’s not that big in reality—essentially appears like a little disk of light, not a mere pinpoint. With a telescope, you can even see that disk.

And whereas pinpoints of light (stars) get disturbed easily as that light passes through Earth’s atmosphere to our eyes, disks of light (planets) will generally shine more steadily.

To see that disk of Mars – or of Mercury, Venus, Jupiter, or Saturn – through a telescope, join us at our next monthly skywatching session at Jordan Lake. If the weather permits, we’ll be at Ebenezer Church Recreation Area on Thursday, August 11, 2016, from 8:30 to 10:30 p.m. All five planets that can be seen with the unaided eye will be above the horizon near the beginning of the session. As a bonus, some Perseid meteors should streak across the sky as well.