While you’re enjoying Monday's full moon -- the harvest moon -- check out the "king" and "queen" of the planets in Rochester's September sky.
As darkness sets in, look for them side-by-side in the low southeast sky. They’re the brightest star-like objects there.
Jupiter, the king of the observable planets from Earth, is to the left of Saturn and is brighter than the queen. Both reached their closest approaches to Earth last month, but they’re still pretty close, at least relatively. This weekend, Jupiter is 386 million miles away, while the tape measure to Saturn would be 861 million miles and change.
Jupiter is by far the largest planet in our solar system, and is mainly a big ball of hydrogen and helium gas. Its polar diameter is about 83,000 miles, and the diameter at the equator is a little more than 88,000 miles. Jupiter is fatter in the middle because of its rapid rotation. It only takes 10 hours to make one complete rotation. The resulting centrifugal force works against gravity to cause Jupiter to bulge along its equator.
Through a small telescope, it's possible to see at least some of Jupiter’s darker cloud bands made up of methane, ammonia and sulfur compounds. You can especially pick up on at least two darker cloud bands on either side of Jupiter’s equator. You may even see some subtle color to them.
You’ll see more bands and detail with larger scopes, and you might even see the Great Red Spot, a giant storm raging on Jupiter. It’s called the red spot, but in reality it will show up in a larger scope with a pale pink hue. The red spot isn’t always available, however, because of Jupiter’s speedy 10-hour rotation. Half of the time the red spot is turned away from Earth.
As I've said 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 periods.
No matter how big or small your telescope is, you’ll get a kick out of watching Jupiter’s four brightest moons; Io, Europa, Callisto, and Ganymede. They orbit around the Jovian giant in periods of two to 16 days. Because of their continual movement, they change positions relative to the disk of Jupiter. 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. On some nights, one or more moons may be either behind Jupiter or camouflaged in front of it. If your telescope is powerful enough, you may see the shadow of a moon crossing in front of Jupiter. It’ll appear as a tiny dot against the backdrop of Jupiter’s clouds.
With Jupiter so close to Earth right now there’s a chance of seeing a moon shadow on Jupiter even with a smaller scope. 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.” There are also websites to help you keep up with the moons. My favorite site is from Sky and Telescope at https://skyandtelescope.org/wp-content/plugins/observing-tools/jupiter_moons/jupiter.html.
Jupiter actually has more than 80 known moons circling it, and there are probably many more that haven’t yet been confirmed. The four moons available through backyard telescopes are certainly the largest. 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.
Enjoy the never ending dance of Jupiter’s brightest moons.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul, and author of the book “Stars, a Month by Month Tour of the Constellations,” published by Adventure Publications. Send questions to email@example.com.
The Rochester Astronomy Club welcomes new members and puts on public star parties. Their website is rochesterskies.org.