Stargazers | Planet: By Jove, look — Jupiter is back!


I've missed Jupiter.

That may seem like a corny thing to say, but when you enjoy viewing a planet as much as I do, it's kind of sad to see it leave the evening sky. Yet, since Earth and its planetary companions orbit the sun, that's just what planets do from time to time, so you have to get used to it.

But the great Jupiter is back in the early evening sky now, and it's going to be a terrific season of Jupiter-watching. In fact, Jupiter will reach its official opposition point on March 8. This is when the planet appears in our sky opposite the sun — it rises in the east at sunset and is visible all night long. It's also the day that it is closest to Earth, and therefore appears larger and brighter than any other day.

So, Jupiter, which is always impressive to view through a telescope, is especially impressive right now. It will be quite a sight for the next month or so.

Jupiter has always been one of my favorite planets because it is very active. Here's a planet with a diameter 11 times bigger than Earth's, yet it rotates on its axis once every 10 hours or so. This means that its Earth-facing side changes completely in just five hours and, with patience, sky watchers with a small telescope can easily observe its pastel cloud bands, and sometimes its great red spot, in just one long evening.

What's equally amazing is that Jupiter is made entirely of gas held together by gravity — there is absolutely no concrete matter. Astronauts trying to land would just sink deeper and deeper into its murky atmosphere until they became crushed by gravity's tremendous weight.

Perhaps the most enjoyable part of watching this planet is keeping up with its four largest moons. They are named the Galilean satellites — Io, Europa, Ganymede and Callisto — because the Italian astronomer Galileo discovered them about four centuries ago.

These Jovian moons do-si-do around the planet's gaseous ring every night. They frequently vanish behind the Earth-facing side, or show in front of the planet while casting shadows onto its cloud tops. Sometimes, a sharp-eyed observer can see movements happen in a flash, such as one moon passing another, or a moon approaching or receding from the disk.

It's even more fun watch these moons if you know which is which. Learn to identify them by downloading an app or by visiting the Sky & Telescope website. To learn even more about these incredible moons and their parent planet, check out the Nine Planets website.

To view the beautiful Jupiter, aim your telescope in its direction, or, contact a local astronomy club or science museum to see if they'll be hosting a free star party so you can get a close-up look at this exciting giant planet.

Yes, indeed, it's going to be another great spring of Jupiter-watching.

Visit Dennis Mammana at


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