For those folks in Los Angeles (and parts of Nevada, Idaho, western Montana, Calgary and Edmonton): if you are up at 03:34 Pacific time tonight, you can watch as an asteroid blocks the light of a naked-eye star!
Sky and Telescope has the details. Basically, the asteroid 824 Anastasia will pass directly in front of the star ζ (Zeta) Ophiuchi. At magnitude 2.5, the star is easily visible, about as bright as Polaris (though honestly, from LA you may need binoculars). The map shown here on the left is from Sky and Tel; click it for a higher-res version. The asteroid itself will be invisible to the eye; it's at magnitude 14.7, a thousandth as bright as the faintest object you can see even from a dark site. But when it passes in front of the star, the star will dim or blink out for up to 8 seconds. This occultation, as it's called, is important because by mapping exact locations and timing from a large number of observers, the shape of the asteroid can be found! Well, more or less, since we only see it in profile, but it's still a nice clue to the characteristics of an otherwise featureless point of light. So if you plan on being out and about at that time, why not check out how to do some astronomy from literally your back yard? The more people who participate, the better our science is!
Image credit: Sky and Telescope.
