Right now, a lot of planets are visible in the night sky. A great alignment, which occurs when all the solar system’s planets are visible at once, has just ended, but you can still spot most of them except for Mercury and Venus, which have already dipped below the horizon.
So naturally, for the past month, my phone has been dinging with friends’ pictures of the sky, accompanied by, “Hey, what planet is this?” or, “This is Mars, right?” As the designated Space Friend, I am expected to know these things, but I’ll be honest – I just pull up a sky map for the night and check my answers that way.
But since a sky map (or a Space Friend) isn’t always available, here are some ways to figure out if you are, in fact, looking at a planet – and which one it might be. The first rule of thumb you may know is that stars twinkle and planets don’t. This is because stars are so much more distant that their light comes to us as a tiny, thin beam, which gets tossed about by our atmosphere, causing it to appear to twinkle. The beam from planets, however, is much broader because they are relatively nearby. This means that when the atmosphere makes light wiggle within this wide beam, we can’t really see it, so planets appear to shine steadily.
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It’s not always easy to tell if a point of light is twinkling or not, so another clue is the object’s location. While you won’t be able to see the planets moving, just as you can’t tell that the sun is moving every day (imagine how terrifying it would be if you could), they do follow a predictable path.
That path, called the ecliptic, is the same one the sun follows. It runs roughly east to west through the sky, and the planets are always near it even if they aren’t perfectly aligned. So if you see a bright star away from the ecliptic, that’s all it is – a bright star.
The last clue is colour. If you look closely, Mars really does appear red in the sky. This is why so many ancient cultures called it red despite its surface looking more orange, and why we call it the Red Planet. Mercury and Saturn (upper-right dot of light, above) both have a yellow tinge, for the eagle-eyed.
Once you are pretty sure it’s a planet, you can try to figure out which one. Mercury is always fairly close to the sun, so you will only be able to see it right after sunset or just before sunrise. Venus is a little farther away, but always in the sun’s vicinity, so if you see a very bright point of light near the horizon at those times, that is likely to be Venus. If you see one point of light that is far brighter than the surrounding stars, it is probably Jupiter. Saturn and Mars are a bit harder to tell apart from the others, but their colours can help. Uranus and Neptune are too far to be viewed with the naked eye.
If all else fails, there are many good sky map options in apps and online. Or you can send a message to your Space Friend – and if you haven’t got one, I will volunteer.
Leah Crane is a features editor at 91av based in Chicago
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