Jupiter brightens up a celestial neighborhood

SkyCaramba astronomy blog for the week ending July 30, 2011

Jupiter is well placed for viewing before sunrise. As dawn’s light increases, you’ll find the gas giant about halfway up the eastern side of the sky. If you’re far north, look a bit southeastward. If you’re far south, look northeastward. Jupiter’s the brightest thing in that part of the sky right now.

Jupiter and moonsIf you have a telescope, you’ll know Jupiter by its telltale cloud bands striping the planet’s disk. Binoculars are enough to see the big dot that is Jupiter with a few smaller dots lined up nearby. They are the moons that Galileo saw. The closest is Io. Next is Europa. Ganymede is third closest, and Callisto is farthest. Sometimes they disappear in Jupiter’s shadow or hide in plain sight right in front of the planet. Those are just four of more than 60 natural satellites orbiting Jupiter. Io is slightly larger than Earth’s moon which will pass by Jupiter around August 20.

When a bright object like Jupiter is in an area of the sky where the stars are dim, it’s a good time to learn to recognize the constellations those dim stars form. Months or years later after the planet is gone, you can still recognize the constellations.

Let’s start with something easy. East of Jupiter is a V shaped asterism called the Hyades. Those stars are the horns of Taurus the bull. The brightest of that group is orange Aldebaran. It’s 65 light years away. In Arabic, its name means follower because it follows the Pleiades. You may have noticed that cluster of stars a little north of the line from Jupiter to the Hyades.

Jupiter, summer 2011The Pleiades look like six stars arranged like a diamond shaped kite with a tail. Those stars are also called the Seven Sisters. Numerous legends say only six are visible because the seventh is hiding. Each sister has a name and for each name there’s at least one legend as to why she’s the one who’s hiding.

Jupiter is just north of the head of Cetus. Although Cetus looks more like the sea monster it did to the ancient Greeks, today’s it’s usually called a whale. In the sea monster’s neck is Mira, a star that fades beyond what the naked eye can see then brightens to easy visibility every 11 months. Mira’s getting brighter now and should be brightest in September.

West of Jupiter are two fish called Pisces. They’re tied together as they swim away from an angry fire god.

Aries the ram, north of Jupiter, is rather hard to visualize. All you can really see are the broad horns. Triangulum, further north, is much more obvious. As imaginative as the Greek observers were 1,800 years ago, they thought enough of the simple triangle to name one up there.

Jupiter’s currently moving eastward from morning to morning, but by late August it will appear to be holding still. Then in September, it will reverse course. In late October, Jupiter will be up all night.