Go outside after dark this month and you will see a bright “star” in the night sky.
What is it? The North Star? Absolutely not—the North Star (also called Polaris) is actually the 48th brightest star in the sky. The Dog Star? No, that’s Sirius, which isn’t easily visible at this time of year. In fact, there aren’t any really bright stars visible right now.
So what is it?
Could it be a planet? Almost certainly. Exactly what you’re seeing depends on in what direction you’re looking in the night sky, and when. However, if you’ve noticed an object shining very brightly, it’s very likely to be a planet.
Here’s how to identify exactly what that bright object you keep seeing actually is:
What’s the ‘star’ shining brightly in the south right after dark?
You’re looking at Jupiter, which the Hubble Space Telescope just snapped in a rainbow filter. The gas giant, shining at a magnitude of -2.4, is high in the southern sky right after dark as seen from the northern hemisphere, and it’s unmistakable.
It was at its best back during its opposition in July 2020, but it’s still a great sight from 4.8 astronomical units (au)—the distance from the Earth to the Sun.
If you have a pair of binoculars then point them at Jupiter to see four of its moons—Callisto, Io, Ganymede and Europa. There will appear as pinpricks of light around Jupiter, but in a line. It’s an incredible sight! While you watch them consider that Jupiter has 79 moons … could it soon be 600?
However, almost as incredible is that there’s another planet lurking nearby. Look to the left of Jupiter and you’ll see the ringed planet Saturn. Though it’s 10 times dimmer than Jupiter, this magnitude 1.3 planet is easy to see with the naked eye. Want to see its rings? So get yourself behind any backyard telescope—though prepare to see only a glimpse. After all, Saturn—also at opposition in July 2020—is 9.5 au from us.
Catch these two gas giants while you can because they’re now on the wane, setting in the west during the early morning. By late December they’ll be invisible to us, though not before their “great conjunction,” which occurs on December 21, 2020. On that date they’ll be just 0.5º degrees apart, and appear to shine as one to naked eyes.
What’s the bright red ‘star’ shining brightly in the east a few hours after dark?
You’re looking at Mars. The red planet is soon to come to opposition on October 13, 2020 a time when Earth moves in between the Sun and a planet. At that time the planet in question is as close as it gets (just 0.4 au), so bigger, and because it’s 100% illuminated from our point of view, it’s as bright as it can be in our night sky. Opposition also means, by definition, that it rises at dusk in the east and sets in the west at dawn, or thereabouts.
Mars—the second smallest planet in the Solar System after Mercury—is now shining at magnitude -2.4, which is exactly the same as giant Jupiter despite its disk being about a quarter of the size, but look at it closely and you’ll easily appreciate its red color. To accentuate its redness, try slightly defocusing your binoculars or squint your eyes. Weird, but it works!
So if you’re seeing a bright reddish object looking above the eastern horizon and climbing into the southern sky late at night, you’re looking at Mars. Look in very early October and you’ll see Mars alongside the full “Harvest Moon,” and by mid-October the red planet will be rising at sunset.
If Japan has its way we could soon see Mars up-close in stunning Ultra HD 8K.
What’s the star shining very, very brightly due east a few hours before sunrise?
You’re looking at Venus. A fabulously bright, white object shining at magnitude -4.1, Venus has cloud-tops, which make it hugely reflective. Those same cloud-tops may—just may—contain microbial life if this month’s discovery of phosphine at Venus is anything to go by.
It’s actually only about 70% illuminated at the time of writing, but it’s still comfortably the brightest planet of all. In fact, it’s now a dazzling sight for early-risers.
How planets move
All planets are found on the ecliptic, the path the Sun takes through the daytime sky. Since the Solar System is flat and all the planets orbit the Sun on the same plane—more or less—you’ll only ever find planets on the ecliptic. This line in the sky essentially stretches between east and west, though only from the equator does it pass overhead.
Right now, as seen from the northern hemisphere, the ecliptic is about mid-way up from the horizon (depending on your exact position on the planet). What that means for planet-spotting is that planets rise in the east, move across the ecliptic in the southern sky, then set in the west.
How to get a head full of planets
The night sky is a moving map that can be navigated and known.
Spend a few minute each week, or even just each month, watching how the planets gradually change position, and you’ll soon instinctively know what’s “up” and what’s not. Do that and you’ll have a real-time map of the Solar System in your head for the rest of your life.
Now that’s a valuable perspective on life, the Solar System and everything else that nobody should ever underestimate.
Wishing you clear skies and wide eyes.