Comet NEOWISE has dominated sky news, but I don’t like to miss a Jupiter opposition. About every 13 months Jupiter and the Earth line up on the same side of the sun and come closest together. Because the planet appears directly opposite the sun — rising in the east when the sun sets in the west — it’s said to be at opposition.
Today, 385 million miles (619 million km) separate the two planets. But next Jan. 29, when they’re on opposite sides of the sun, they’ll be 179 million miles (289 million km) farther apart. That’s a significant difference and the reason why Jupiter looks so incredibly bright right now. Closer also means the planet appears bigger when viewed through the telescope. And bigger is always better for seeing planetary detail.
Jupiter is currently the brightest planet in the evening sky, rising in the southeastern sky during evening twilight. It’s joined by Saturn, located just 7° to its left (east). They’re so close together you won’t be surprised to learn that Saturn comes to opposition less than a week later on Monday the 20th. That’s not all. Dwarf planet Pluto is at opposition today, July 15 — a trifecta! To see the 14th magnitude blip you’ll need at least a 10-inch telescope.
Through a pair of 7x or 10x binoculars Jupiter has a distinct shape and depending on when you look, up to four of its moons are visible. The planet has 79 confirmed satellites, but all but four are faint and small. Because Galileo was the first to see the quartet they’re known as the Galilean moons — Io, Europa, Ganymede and Callisto. Each orbits Jupiter with its own period, so every time you look at the planet in binoculars or a telescope (better) you’ll see a unique arrangement.
Telescopes show the moons not only off to either side of the planet but also when they pass in front of it during transits. You can sometimes see the moon itself hovering above Jupiter’s cloud tops during a transit, but the tar-black shadows (shadow transits) they cast are much easier to spot. Jupiter casts a shadow just like the Earth. When one of its moons passes into the shadow it temporarily disappears in eclipse. All this makes for wonderful, summer night entertainment for skywatchers. To find out which moon is which and for a list of upcoming eclipses and transits check out Sky & Telescope’s Jupiter’s Moons.
Most small telescopes will show two dark, horizontal stripes across the planet called the North and South Equatorial Belts. Thinner temperate belts are visible north and south of the pair. Use low magnification to first find the planet and center it in the scope’s field of view, then increase the magnification to pick out more details. Jupiter has no solid surface. Everything you see are clouds made of ammonia ice crystals mixed with sulfur and phosphorus compounds that add extra color.
The most colorful feature on the planet is the Great Red Spot, an oval storm a little larger than our entire planet that’s been whirling around up there for more than three centuries. You’ll need a 6-inch telescope and magnification around 100x-150x for a clear view. From mid-northern latitudes Jupiter is rather low in the sky this season, meaning it’s more affected by atmospheric turbulence. Don’t be surprised if some nights it looks blurry through the scope. Back off the magnification and enjoy the moons instead. On nights when the air is steady and the planet super sharp, crank up the magnification and see how many cloud belts and other atmospheric details you can eke out.
All this is easy to do because you’re out looking at the comet anyway, right? When you’ve had your fill of that sky wonder, turn around and point those binoculars at the largest planet in the solar system. Did you know 1,300 Earths could fit in there?