StarDate 5/28/2014: Tracking Down False Comets

FROM THE UNIVERSITY OF TEXAS McDONALD OBSERVATORY, AS HEARD ON KCBS RADIO WEEKDAYS @ 9:52 A.M., 7:35 P.M. & 2:52 A.M.

STARDATE 5/28/2014: For an 18th-century astronomer, the quickest way to fame and fortune was discovering comets — the big iceballs that grow long, beautiful tails when they come close to the Sun. But seen through the telescopes of the day, a comet that was still far from the Sun looked like nothing more than a faint, fuzzy star. And a lot of other astronomical objects had a similar appearance.

To keep down the number of false alarms, French astronomer Charles Messier set out to catalog these comet-like objects. And 250 years ago this month, he made his first independent discovery: an object in the constellation Canes Venatici, the hunting dogs. It's known today as M3 — the third object in Messier's catalog.

It's a globular cluster — a dense ball of stars. Most estimates say it has about a half-million stars packed into a spherical region of space just 180 light-years across.

The cluster is part of our home galaxy, the Milky Way. But it's not in the galaxy's broad, thin disk. Instead, it's about 30,000 light-years above the disk, in a region known as the halo. In fact, when you look at M3 you're looking straight out of the disk and into the vast reaches of intergalactic space.

M3 is high in the southeast this evening, well above the bright yellow-orange star Arcturus. It's too faint to see with the eye alone. A small telescope begins to show its true nature — a massive cluster of stars high above the Milky Way.