Jupiter's putting on a great show this week
Right now it's high and bright in the early evening southeastern sky, close to the overhead zenith. It's the brightest starlike object in the sky right now.
Jupiter is about 413 million miles away with a diameter of 88,000 miles, more than 10 times the girth of our world. In fact, if Jupiter were hollow you could fill it with more than a thousand Earths.
The moon joins the show this week. Tonight the waxing gibbous football-shaped moon will be just a little to the left of Jupiter, and on Monday night they will be in a very tight celestial hug. The moon will be just 1 degree to the left of Jupiter. That's only the width of your forefinger at arm's length.
The pathes of the moon and Jupiter are nearly in the same plane. The moon rips among the backdrop of stars as it orbits our Earth in a little over 27.3 days. It takes Jupiter 12 years to make the same circuit, obediently circling the sun every dozen years.
Jupiter also has its own moons, well over 60. Four of its largest moons can be seen on either side of the planet with a small telescope or even a decent pair of binoculars. They look like stars. With a small telescope you should also be able to see at least some of the methane and ammonia cloud bands across Jupiter's face.
The number of moons you see and where they are with respect to Jupiter depend on where they are in the 2- to 17-day orbits around the big guy. The moons pass behind Jupiter on a regular basis and are lost from our sight, and they also pass in front of Jupiter and get camouflaged against the planet's clouds.
Galileo Galilie (1564-1642) also spotted Jupiter's largest moons, which helped him prove that the sun, and not Earth, is the center of our solar system.
Galileo was the first person on record that really studied the sky with his crude telescope. He was trying to convince the world that Copernicus, who lived before Galileo's time, was correct in claiming that the Earth was just one of the planets circling the sun.
If you visit Florence, Italy, you can see Galileo's historic telescope at the Florence Museum of History and Science.
Almost 410 years later, Galileo once again made new discoveries about Jupiter and its moons, only this time it was the Galileo space probe. Before Galileo, the Pioneer and Voyager probes gathered pictures and data of the Jovian system. Because of these missions and other observations, we know a lot more about Jupiter's moons, especially the four big Galilean moons.
The two outer moons, Callisto and Ganymede, are old crater covered moons, about 4 1/2 billion years young and not all that interesting except for the fact that Ganymede is the largest moon in our solar system, more than 3,400 miles in diameter.
Jupiter's closest moons, Io and Europa, are anything but boring. Io, the closest moon, has numerous active sulfuric volcanoes and constant lava flows because of the tremendous tidal stress from its mother planet.
When the first color photographs of Io came back astronomers dubbed Io the "pizza planet" because it was various shades of orange and red from all of the volcanism on its surface.
The second closest moon, Europa, may have a slushy ocean under a thin layer of ice. It could be the only other place in the solar system besides Earth that has liquid water, and where there's water, possibly life? Stay tuned.
In the diagrams are the positions of Jupiter's moons relative to the planet over the next seven nights. A good website to keep up with the whirling Galilean moons is from Sky and Telescope Magazine: tinyurl.com/4v4pww.
There are also many apps that keep up with Jupiter's moons on both Android and iPhones.
Mike Lynch is an astronomer and professional broadcast meteorologist.
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