So you’ve probably heard that tonight, Jupiter is as close to Earth as it’ll get in many years. While this is true, and pretty cool — and I certainly don’t want to damp enthusiasm for anyone wanting to go outside and see it! — I want to make sure you understand what this means.
First of all, this whole thing is happening because Jupiter is at opposition: that is, it’s directly opposite the Sun in the sky. A better way to think of this is that the Earth is passing very nearly directly between the Sun and Jupiter, so from the Earth we see them on opposite sides of the sky. At this point, the Earth is as close to Jupiter as it can get for that particular orbit. Both Earth’s and Jupiter’s orbits are slightly elliptical, so sometimes Jupiter gets a bit closer to us at opposition than other times; this year is the best in decades. It’s about 590 million km (355 million miles) away. That’s still a pretty long way!
But Jupiter is a big planet, 140,000 km (86,000 miles) across, almost 11 times wider than the Earth! It’s also a whitish color, so it reflects a lot of sunlight. Its size, reflectivity, and close distance together make it a very bright object in the sky. If you go outside any time after sunset tonight you’ll see it in the east, a luminous beacon glowing brilliantly.
However, some people have been saying that tonight is the best night to see it, and we won’t get a chance to see it like this again for years. Shades of the Mars Hoax! In reality, it doesn’t matter if you go out tonight, or wait a few days. While technically Jupiter is closest right now, it’s not like it’ll be a lot farther away tomorrow night. Here’s why.