Big, Bright Two-Spotted Jupiter Dominates the Evening Sky

(Updated Aug. 1) - Look south after dark this month, and you'll see a bright white "star" looking right back at you. This is the planet Jupiter, shining so brightly that you can't help but notice it even through city light pollution.

Jupiter blazes so bright mostly because it's a big planet, but also because on May 3 it was at opposition: positioned opposite the sun in our sky and at its nearest to Earth for the year. Jupiter will remain nearly as bright throughout the summer, since it doesn't get much farther from us even several months after opposition. It will be the "star" of all the warm-weather nights in 2006.

Telescope users have been following a strange event brewing on Jupiter. Amid the planet's cloud belts, a long-enduring "white oval" unexpectedly turned reddish last February -- matching the color of Jupiter's centuries-old Great Red Spot. Both amateur and professional astronomers have been tracking "Red Spot Junior." This small red spot was set to converge with the Great Red Spot between July 15-20; see NASA story.

Jupiter's spots are enormous cyclonic storms somewhat like hurricanes on Earth. White ones are topped by clouds of ammonia crystals in Jupiter's super-cold upper atmosphere. The reddish tints, planetary astronomers believe, arise from contaminant compounds of sulfur, phosphorus, or hydrocarbons welling up from inside Jupiter's mysterious, gaseous interior.

To see the Great Red Spot and "Red Spot Junior," you'll need a large amateur telescope with high-quality optics. Jupiter rotates once every 9 hours 56 minutes; a list of times when the Great Red Spot crosses Jupiter's centerline, as seen from Earth, can be generated online for any date at skyandtelescope.com/ redspot. "Red Spot Junior" follows behind about 1 hour 10 minutes after the Great Red Spot.

To learn what else is up during August, see 'Touring the August Sky.' Discuss observing tips and successes on our sky watching message board.