Astro Bob: How to use binoculars to see Jupiter’s bright moons – Duluth News Tribune

A moon is a natural satellite that revolves around a planet or asteroid and glows with reflected sunlight. There are more than 200 known planetary moons in the solar system, but most of us have only seen one – Earth’s moon. With an 8-10 inch telescope and dark skies you can add about 14 more. Not many people own an instrument of this size, but many of us have binoculars lying around. Luckily, that’s all you need to see at least two and possibly four additional moons.

The second brightest after our own moon are the four Galilean satellites orbiting Jupiter. They range from magnitude 4.6 for Ganymede to 5.6 for Callisto. If they were distant from the giant planet, all would be visible to the unaided eye from a dark sky, but they orbit close enough to suffer from Jupiter’s bright glow.

Galileo discovered the quadruple in early 1610 using a home-made 1.5-inch (37mm) telescope with 20x magnification. They are called Galilean moons in honor of his achievement. Jupiter has 80 known satellites, but these are the only ones bright enough to be seen in even larger amateur telescopes.

Each of them has its own orbital period, just like the planets around the Sun: Io is closest, rotating once in just 1.8 days; Europe in 3.6 days; Ganymede at 7.2 days and Callisto at a leisurely 16.7. That’s why you’ll never see them in the same positions night after night. You keep getting it mixed up. Observers have likened her movements to a ballet. Once you watch it, you will agree with me.

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I got my first good look at Jupiter and its satellites when I was 11 through a cheap Japanese refractor telescope that my parents bought me. The planet was bright and clear, with the moons neatly aligned in a row on either side – a perfect family. How could it be so easy to see something so remarkable? That first impression is still fresh in my memory to this day.

Jupiter in binoculars
This binoculars simulation shows Jupiter and its moons on Tuesday evening, October 25th, around 8pm Central Time. Europa and Ganymede will likely be too close to separate in most binoculars and will appear as a single point of light.

Contributed / Stellarium

Even if you don’t have a telescope, you can spot the moons with 7x to 10x binoculars. To aid your search, use the included nighttime guide that shows their locations. I purposely scaled the simulations down to resemble what you might see at very low magnification. Sometimes two moons appear too close together to tell them apart, so I’ve labeled them “E+G” or Europa plus Ganymede, for example. Ganymede and Callisto are the easiest to see because they orbit farther from Jupiter and better escape its glare.

Jupiter moons panel
These miniatures show the arrangement of Jupiter’s moons at 8 p.m. Central Time (CDT) from October 26 to November 2, 2022. I = Io; E= Europe; G = Ganymede and C = Callisto. The reason one or more moons are missing on some nights is because they are temporarily in front of, behind, or obscured by the planet’s shadow.

Contributed / Stellarium

Io and Europa are trickier because they orbit closer together and are often swamped by the planet’s bright glow. Persistence pays off in the long run, especially for observers with binoculars with a magnification of 10x or more.

binocular viewing
If you have steady hands, you can hold the binoculars and spot several of Jupiter’s moons. A better way is with some help from a pole, wall, car roof or tripod. I found the outermost moons Ganymede and Callisto with handheld, but need to “plant” the instrument to see the inner ones.

Contributed / Bob King

Two things to keep in mind to increase your chances of success: Hold the binoculars steady and focus sharply. Hand-holding is fine for general sweeping and pointing, but to spot the moons, consider propping the instrument against the roof or hood of a car, or mount it on a tripod for best results. Tripod adapters are cheap – Amazon has a wide range.

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Good concentration is essential. Before aiming at Jupiter, aim the binoculars at a bright star and focus as sharply as possible. Then you will be ready to see what radiant Jupiter has hidden from your eyes all these years. Oh, how do you find the planet? Just face the southeast once it gets dark. The big, bright thing you see is Jupiter. Can’t miss it!

The guide included here shows the positions of the moons from October 25th to November 2nd. To know exactly where they are from any location any night of the year, go to Jupiter’s Moons at skyandtelescope.org or download the free program from stellarium. org , set the time and use the mouse wheel to zoom in on Jupiter.

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