Circling a giant

Have you seen that really bright star popping out and dazzling the southeast Marshall sky after sunset? It’s hard to miss! It’s actually Jupiter, the biggest by far planet in our solar system. It’s basically a big ball of hydrogen and helium gas with a diameter of around 88,000 miles, more than 11 times that of our Earth. Through a telescope, even a smaller one, it’s possible to see at least some of its darker cloud bands that appear diagonally oriented as Jupiter rises in the southeast sky. The easiest ones to see are two darker cloud bands on either side of Jupiter’s equator. The clouds are made up of methane, ammonia, and sulfur compounds. There’s actually some subtle color to them.

With larger scopes you’ll see more bands and more detail, and maybe even the Great Red Spot, a giant storm raging on Jupiter. It’s called the red spot, but in reality, it has more of a pale pinkish hue. The red spot isn’t always available, though, because of Jupiter’s speedy 10-hour rotation. Half of the time the red spot is turned away from Earth. As I’ve told you before, the longer you gaze at Jupiter through the eyepiece of your scope, the more detail you’ll see. Try to look at it for at least 10-minute shots at a time. That really works.

No matter how large or small your telescope is or even if all you have is a pair of binoculars you’ll get a kick out of watching Jupiter’s four brightest moons. Io, Europa, Callisto, and Ganymede obediently orbiting Jupiter in periods of two to 17 days. There’s many, many smaller moons gravitationally enslaved by the big guy of the solar system.

Because of their continual dance they will constantly be changing positions relative to the disk of Jupiter. Some nights you may see two on one side and two on the other, or three on one side and one on the other, or all four on one side. There are also many nights when you can’t see all four at one time because one or more moons may be behind of or in front of Jupiter from our Earthly vantage. When a moon is behind Jupiter you obviously have no shot at seeing it, but when one is in front of the disk of the planet you may see the dot of its shadow on Jupiter, although you need a moderate to larger telescope to see this. With Jupiter’s relative proximity this month and most of this upcoming fall, you have a chance of seeing a moon shadow on Jupiter even with some of the smaller scopes. It’s worth a try.

You can keep up on the position of Jupiter’s four brightest moons by checking out monthly magazines like “Astronomy” or “Sky and Telescope,” but of course there are many places to find that information on the Internet. My favorite site is from Sky and Telescope magazine at http://www.skyandtelescope.com/observing/objects/javascript/3307071.html#. You do have to register online but there’s no cost or obligation.

Type that in and click the link they show in red print, and it will produce a diagram of the layout of Jupiter’s moons at any given time. Sky and Telescope also has a great phone app for about $3 that does the same thing. I have it on my phone.

In the diagram I show the positions of Jupiter’s moons during the coming week. This coming Saturday night, if your scope is up to it, you may see the shadow of Io on the face of Jupiter, and this coming Sunday Europa’s shadow will dot the planet’s disk. Consider this extra credit if you see these two shadowy events next weekend.

Jupiter actually has more than 60 known moons and probably many more that haven’t been confirmed yet, but the four larger moons that we see through our backyard telescopes are certainly the best known. They’re also referred to as the Galilean moons, because the great astronomer and scientist Galileo used these moons to help prove that the sun, and not the Earth, was the center of what was then seen as the universe.

Io is the closest moon at a little over 2,200 miles in diameter. A little larger than our moon, it’s the most geologically active body in our solar system. Since it’s only about a quarter of a million miles from the very massive Jupiter, there’s a colossal gravitational wallop on Io from the mothership. The tidal forces are tremendous, and because of the constant stretching heat builds up in Io’s interior to the point of melting. This in turn produces numerous and frequent volcanic eruptions.

The next moon out from Jupiter, Europa, may be the best candidate for life in our solar system. Europa is covered by a sheet of ice, and there may be an ocean of liquid water beneath it, or at least a slushy ocean. Once again, because it’s so close to Jupiter the tidal forces are strong enough to heat up Europa’s interior, possibly allowing for liquid water below the ice. Where there is liquid water there’s a chance of life as we know it. Stay tuned!

Callisto and Ganymede are the largest and farthest away from Jupiter of the Galilean moons, and are both larger than our moon. In fact, Ganymede is even a little larger than Mercury, the closest planet to the sun. Both Ganymede and Callisto are heavily cratered bodies and are comparatively nowhere near as interesting as Io and Europa.

Enjoy the never-ending dance of Jupiter’s moons!

CELESTIAL HUGGING THIS WEEK: The moon will have some nice close conjunctions between both Jupiter this week. On Friday. July 12, the waxing gibbous moon will be just to the upper right of Jupiter and on Saturday, July 13, the moon will be just to Jupiter’s left. Don’t miss the show!

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is also the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and at adventurepublications.net.


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