A faint star in the Ophiuchus constellation drew about 30 astronomers from around the globe Friday to Columbia Basin College in Pasco.

The college is the setting for the annual meeting of the International Occultation Timing Association, or IOTA, a group that observes events similar to an eclipse to gather information about the size and shape of celestial objects.

The group will be at CBC through today throwing around numbers about orbital paths and star magnitude the same easy way a baseball fan would rattle off a favorite player's batting average.

But really, they came to observe asteroid 153 Hilda, a hunk of space rock more than 170 miles across.

The asteroid has a dark surface and is hard to see on its own, which is where that faint star comes in, said David Dunham, the association's founder and president.

Occultation timing is all about watching stars blink briefly in and out of sight as they pass behind other objects.

Astronomers can use predictions and known star positions to map the size and shape of an object such as 153 Hilda by observing how long it takes for a star to pass behind it.

When the star disappears, it's being eclipsed by the asteroid. When it reappears, the asteroid has moved on.

Association member Chad Ellington said by knowing the speed of the asteroid and the time it takes to pass the star, astronomers can calculate the distance across.

They learned early Friday morning that 153 Hilda, which is part of the large asteroid belt located roughly between Mars and Jupiter, is about 176 kilometers across horizontally and measures about 149 kilometers vertically.

That's about 109 miles by 93 miles to the average American.

The asteroid is about 400 million kilometers, or about 250 million miles, away from Earth, but Dunham said it's important to collect information about the size and shape of asteroids in the event one skirts through our cosmic backyard.

"It's to understand them better because maybe one of those asteroids has our name on it," Dunham said.

For more information, visit www.lunar-occultations.com/iota/iotandx.htm.