occultation
Image: Courtesy of Sky & Telescope/ E. BONDUELLE

Skygazers in North America can watch a stellar show today as the moon passes in front of Saturn, obscuring it from view. Audience members located east of the Mississippi will have especially good seats: they'll see the event play out in the southern sky against total darkness.

Today's event is a so-called occultation, in which one celestial object blocks another from view. The moon, in its 388,000-kilometer orbit around Earth, will cross the same part of the sky occupied by Saturn (located 1.3 billion kilometers away from Earth) in its trajectory around the sun. Once the moon's dark, eastern limb encounters Saturn, it will take about two minutes for the moon to cover the planet's rings from tip to tip. Saturn will reappear on the moon's bright limb slightly more than an hour later. Viewers located in the northeastern parts of the continent should be able to see the early-evening event (7:25 EST in New York City) without the aid of a telescope, weather permitting. In more southern and western locales, the show is scheduled to begin either in daylight (3:21 PST in Los Angeles) or twilight (5:26 CST in Houston), so telescopes will be required to watch the action.

Though the moon will occult Saturn several more times this year, today's occurrence is the only one with potential to be easily viewed from North America. If you miss this spectacle, your next chance to see it won't come until 2006.