What’s That Bright Star in the Sky? It’s Not a Star, It’s Venus
What’s that bright light in the sky? How come I never noticed it before? That’s not a star at all, it’s Venus, and it is awesome.
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Team: Fraser Cain – @fcain / frasercain@gmail.com
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Every few months a bright star appears in the sky. Sometimes it’s off to the East, bright in the morning before the Sun rises. Other times, you can see it in the West right after the Sun sets.
Experienced stargazers know this isn’t a star at all, of course, it’s Venus. That horrible twin planet, surrounded by a toxic choking atmosphere of superheated carbon dioxide. For a while it becomes the fourth brightest object in the sky: after the Sun, Moon and the International Space Station, if you can believe it.
In dark skies, Venus gets so bright you can even read a book to it.
Inexperienced stargazers, however, suddenly notice this super bright star in the sky. How come they never noticed it before? Was it always right next to the Moon like that? And that’s when the UFO calls to 911 start up.
I know none of them are going to be watching this video. But for everyone else, even mildly interested in the science here, let’s dig into the orbit of Venus, how we finally figured out what that thing is, how you can observe the planet, and some cool tricks Venus can do.
We’ve done several videos on what planet Venus actually is, and why it sucks so much. You know, a runaway greenhouse effect giving the planet 90 times the Earth’s atmospheric pressure at the surface. It’s a 462-degree furnace, anywhere you go, with a rain of sulphuric acid.
Nope, we’re not going to talk about visiting that place. Instead, we’re just going to talk about looking at it from afar, and how it changed our whole understanding about our place in the Solar System.
Venus is, of course, the second planet from the Sun. But for the vast majority of human history, nobody really understood what it was. It’s easy to see in the sky, even if you live in one of the most light polluted cities on Earth.
Ancient civilizations tried to grapple with what they were looking at, and of course, they assumed there was something supernatural going on. Probably dark and vengeful gods wandering through the heavens, staring down at us with their beady eyes. Judging, always judging. Some civilizations figured out that it’s a single object, while others believed they were looking at two separate entities.
The Ancient Greeks, for example, called the morning edition of Venus Phosphoros, the “Bringer of Light”, and they called the evening star Hesperos, the, uh, “Star of the Evening”. Then they realized it was a single object, and upgraded it to Aphrodite, the goddess of love. The Romans turned that into Venus, and the name stuck.
The ancient astronomers assumed the Earth was the center of the Universe, and all the planets and even the Sun and stars revolved around us. but Nicholas Copernicus worked out the true nature of the Solar System in the early 16th century. The Sun was at the center of the Solar System, and all planets, including Earth, orbited around it.
It was a cool story, and nicely fit the motions of the planets, however, the best evidence came almost a century later when Galileo turned his first crude telescope to Venus and realized that the planet goes through phases, just like the Moon.
In fact, with a small telescope, you can confirm this all for yourself.
Each of the planets orbit the Sun. Mercury and Venus orbit closer to the Sun, then Earth, then the rest of the planets. When we observe Venus, we look inwards, down towards the Sun. When we see the rest of the planets, we’re looking outward, away from the Sun.
The best analogy is a car race. If you’re in the stands watching those cars go around and around, you’re turning your head back and forth as the cars pointlessly circle in front of you. But to see cars in the ring road around the racetrack, you’ll need to look all the way round you. Make sense?
Here’s a simplified version of the Solar System, with just the Earth, Venus, and the Sun. Earth, as you probably know, takes just over 365 days to go around the Sun, while Venus only takes 225 days to complete an orbit.
Which means that Venus completes more than 3 orbits every time Earth completes 2. Which means that we’re always seeing Venus from different angles compared to the Sun.
Sometimes it’s on the same side of the Sun as us. Other times it’s on the opposite. And sometimes Venus is on one side of the Sun, or the other.