Friday, June 22 , 2018, 7:45 pm | Fair 62º


Dennis Mammana: Jupiter’s Moons a Highlight of the Big Planet’s Return

Jupiter Click to view larger
View the return of Jupiter after dark this week. (Dennis Mammana illustration /

An exciting spring and summer of stargazing — or should I say planet gazing — lies ahead, as four neighboring worlds prepare to strut their celestial stuff.

Right now, anyone stepping outdoors at dusk will see the brilliant planet Venus glistening low in the western sky. It’ll be there all summer long, and believe it or not, it will become twice as bright by September.

Then there’s everyone’s favorite planet, Saturn, which isn’t in our early evening sky right now but will be by the end of June. It will provide those with even a small backyard telescope a close-up of its remarkably beautiful ring system.

Late in July, the red planet Mars will become a stunning sight in our nighttime sky as it reaches its nearest point to the Earth in the past 15 years. We will not see it as close and bright again until 2035.

And then there’s the giant planet Jupiter. This great world is in our evening sky right now and will reach its official opposition point on the night of May 8. 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 in its orbit.

So, Jupiter, which is always impressive to view through a small telescope, will be especially impressive this month. In fact, it will be quite a sight throughout much of the summer.

Jupiter has always been one of my favorites because it’s a planet that actually appears to change fairly quickly. 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, early evening 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.

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 motions some four centuries ago.

These appear to do-si-do around the planet and change their positions from night to night — sometimes even from hour to hour!

Much of the fun of watching these moons is knowing all their names. You can identify them by finding an app for your smartphone or tablet, or click here for more information from Sky & Telescope. You can click here to learn more about these incredible moons and their amazing parent world at Nine Planets.

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

Yes, indeed, it’s going to be another great spring and summer of planet gazing!

Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at [email protected] and follow him on Twitter: @dennismammana. Click here to read previous columns. The opinions expressed are his own.

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