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By Jove, Jupiter Is Back!

Skywatch

By Dennis Mammana- I’ve missed Jupiter.
That may seem like a corny thing to say, but when one enjoys viewing a planet so much, it’s really kind of sad to see it leave our evening sky.

Yet, since Earth and its companion worlds orbit the sun, that’s just what planets do from time to time, so one must get used to it.

But the great planet is back in the early evening sky now, and it’s going to be a terrific summer of Jupiter-watching. In fact, Jupiter will reach its official opposition point on June 10; not only is this when the planet appears in our sky opposite the sun (rising in the east at sunset and remaining visible all night long), it’s also when it lies closest to Earth and, therefore, appears larger and brighter than at any other time of its orbit.

So, Jupiter, which is always impressive to view through a small telescope, is especially impressive right now. In fact, it will be quite a sight for the next few months.

Jupiter has always been one of my telescopic favorites because it actually seems to do something. Here’s a world that’s 11 times the diameter of Earth, 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; with patience, sky watchers with a small telescope can easily watch its pastel cloud bands and, sometimes, its Great Red Spot spin completely around in just one long evening of stargazing.

Equally amazing is knowing that Jupiter is made entirely of gas held together by gravitation: There is no surface on which to stand. Hypothetical astronauts trying to “land” on the planet would just sink deeper and deeper into its murky atmosphere until they’d become crushed beyond recognition by its tremendous weight.

Perhaps the most enjoyable part of watching this planet is keeping up with the antics of its four largest moons. These are known as the Galilean satellites —Io, Europa, Ganymede and Callisto — because it was the Italian astronomer Galileo who discovered them and their movements some four centuries ago.

These moons do-si-do around the Jovian disk from night to night. They frequently vanish behind Jupiter or slip in front of the planet while casting their shadows onto the giant world’s cloud tops. And sometimes, if two moons are passing one another or approaching or receding from the planet’s disk, a sharp-eyed observer can see their movements in only a few minutes.

Much of the fun of watching these moons is knowing which moon is which. You can identify them by finding an app on your smartphone/tablet or by visiting the Sky & Telescope website. And to learn more about these incredible moons and their amazing parent world, be sure to check out the Nine Planets website.

Now that Jupiter has returned to our early evening sky, try aiming your telescope in its direction or contact your local astronomy club or science museum to learn when they’ll be hosting their free “star party” so you can get a close-up look at this exciting, giant planet.

Yes, indeed, it’s going to be a great summer of
Jupiter-gazing!

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