Most such links were naïve: Reddish Mars became associated with fire or blood. Saturn's slow movement made people think that it was gloomy. But the ancient Greeks and Romans hit the target when it came to the largest planet: Jove may not be jovial, but it deserves its moniker as king of the gods.
Right now, it rules the night. Jupiter is simply the brightest "star" in the heavens. Its creamy dazzle makes it a lighthouse in the southern sky, in Sagittarius. It reaches its closest approach to Earth today (Thursday, July 10) and will remain fabulous for the next three months.
Jupiter's so conspicuous because it's relatively close to us - a situation that recurs every 13 months, when our faster-moving Earth catches up with the sleepy Goliath. As it's overtaken, Jupiter seems to move backward like a truck being passed on the highway. To the ancients, such retrograde motion was as strange as Karl Rove. Too bad no one back then ever hit upon the correct, simple explanation.
Jupiter will remain the night's brightest "star" all summer long, and telescopically appears larger than any other planet, though three others are nearer to us. Galileo, using a truly pathetic low-power instrument, peered at Jupiter in 1610 and instantly revised the universe - a 400-year anniversary that will soon make major-media headlines. Four moons conspicuously circled Jove, the first proof that Earth is not the center of all motion. Lined up like tracklights, those four dots can be seen today even through steadily braced binoculars.
Impress your friends: Announce them by name. The inner one, Io, an orange world of violently erupting volcanoes, zips around Jupiter in just 1.77 days, changing position while-U-wait. The next-nearest moon, Europa, orbits in exactly twice as long: 3.55 days - still impressively fast when you remember that our own moon requires nearly a month. Beneath Europa's ice-crust lurk warm liquid oceans and goodness-knows-what-else. Then, moving outward: Ganymede is the solar system's largest satellite, with a 3,279-mile diameter. You can quickly spot it because it's the brightest. Watch it make one circuit per week - a period twice Europa's and four times Io's.
Such a simple 1:2:4 orbital relationship means that the moons resonate with each other, gravitationally locked in synch like a cheerleading team. Finally, farthest from Jupiter there's giant Callisto - larger than Mercury or Pluto. Five dozen other moons have been found, but they're tiny 20-mile chunks of debris, not in the same league as the Galilean heavyweight quartet.
Any small scope lets you check out Jupiter's bands, running parallel to its Equator. With a spin speed 25 times faster than ours, it's no wonder that Jove's main features are horizontal streaks. If conditions are steady, you might also see white ovals, swirls, festoons and the Red Spot, which is often a grayish-pink. Jovian markings rush in frenzied fashion thanks to its snappy 10-hour rotation. Powerful stuff, that the largest planet also boasts the solar system's fastest spin. Its Equator races along 50 times faster than a bullet, making the whole planet bulge outward at the Equator.
Jupiter is the award-winner for planetary observers, and will dominate the sky all summer. Any department-store telescope will show some details. If you're not satisfied with the view, return the instrument. Galileo had to deny what he saw for fear of death; the refund policy at most Kingston stores is less intimidating.
Post a Comment