Asteroid occultation timing

¡SkyCaramba! Weekly astronomy blog for the week ending March 15, 2014

Asteroids are rocky objects orbiting the sun much like planets do. They’re often described as minor planets. Unlike major planets, asteroids don’t have their own atmospheres as far as we know. But a few have moons. They’re being orbited by other asteroids!

Major planets are round, but asteroids come in many shapes. Some are roundish, some are like ovals, and some are very irregular. There’s one shaped like a peanut. There are many asteroids astronomers don’t know enough about to say what shape they are. Asteroids are so small, the first ones discovered were just star-like points of light in the best telescopes of the time. The word asteroid actually means star-like object.

Since asteroids are some of the smallest objects in the sky and they don’t reflect a lot of sunlight in the first place, they are very dim. So it’s hard to know exactly how big they are and what shape they have. Fortunately, astronomers are very good at figuring out asteroid orbits. And they’ve figured out how to use the light from distant stars to learn their shapes.

When an asteroid passes directly between Earth and a distant star, some careful observers on Earth will see the star disappear. Many will not. The event is called an occultation. The people who don’t see the star at any given moment will be in an area that resembles the shape of the asteroid.

To determine the asteroid’s shape, those observing must report exactly when the star vanishes and reappears. Astronomical organizations that specialize in these observations suggest making a sound recording that starts before and ends after the occultation. The observer, using a clock or watch set to the correct time, should occasionally say exactly what time it is—including the second.

An even better idea is to have a radio tuned to a time signal station. Shortwave radio listeners are familiar with WWV and WWVH which tick away every second of the day with voice announcements just before each minute starts. The sound from this broadcast can be played into a microphone at about the same volume as the observer who’s telling what he or she sees. Even better than that would be to have the time signal audio fed into one channel of a stereo recording while the observer uses a microphone that feeds the other channel.

Hopefully, if you live in the northeast United States or eastern Canada, you’ve heard of the occultation of Regulus that will happen on the morning of March 20, 2014. An asteroid named Erigone will pass in front of that very bright star. Astronomers believe the visibility path for this occultation will be 45 miles wide. But just in case they’re wrong about Erigone’s size and shape, you should look for the occultation if you’re a few miles outside the path.

And if you can, contribute your observation to one of the occultation timing organizations listed in the links below. A visibility map can also be found through the links below.