(I know it’s a weird headline, but try coming up with something short that explains this!)
If you live in southwest Georgia or northeast Florida, on Tuesday evening April 17th at 8:56 p.m. local time, you might see the star Iota Cancri blink out as an asteroid named Xanthe passes in front of it.
This type of event is called an occultation. The asteroid’s orbit takes it right in front of a star, and the star appears to wink out or drop in brightness. Because asteroids are small, a specific occultation can only be seen along a narrow corridor, which is why those parts of Georgia and Florida get to see this. This particular one should be really nifty, too, since Iota Cancri is a visible star, shining at magnitude 4.2 (meaning it’s easily visible from dark skies, though people near bigger towns might need binoculars to see it).
These are more than just curiosities, too. By getting careful timings of the occultation from observers at different locations, the shape of the asteroid can be determined! Imagine the asteroid is a perfect sphere. The path of the occultation would be easy to predict, and people north and south of that line would see the asteroid “miss” the star.
Now imagine a small hill on the asteroid. An observer on Earth slightly farther north might still see the occultation! So very precise timing and location measurements can provide a pretty good projection of the asteroid’s shape. To learn how to get timings, read what they have about it at the International Occultation Timing Association’s site. And get out there and observe!