The cosmos, the heavens, the infinite. It's all right there over our heads, all the time. Go outside and look directly up after dusk. Besides the space junk, the low-flying Piper Cubs, police surveillance helicopters, commercial aircraft and fighter jets, there are visible stars, planets, astral bodies -- out-of-this-world stuff. How cool is that? The most practical place to view the night sky, of course, is wherever you happen to be standing, but the bright lights of the city make for less-than-ideal conditions. So what are aspiring astronomers to do if they can't afford a $1,000 telescope or the gas money to drive two hours out into the boonies? Well, they can visit the little-known observatory at Washington University, which is open to the public. It's not Mount Palomar, but the vantage point from the dome on top of Crow Hall offers an opportunity to take a free peek at the craters of the moon or a closer look at Venus. Whereas modern-day students scour the universe through radiotelemetry, the Wash. U. observatory offers something different -- a view of astronomical history. The observatory's telescope dates back to the founding of the university in 1857, when philanthropist James Yeatman donated $1,500 to build it. The instrument is now considered so valuable that the Smithsonian Institution has expressed interest in acquiring it. But Wash. U. has no plans to take it out of service at this time. The observatory and telescope were originally located at the university's downtown campus on St. Charles Street and served as a source for standardized time for the region. Scientific studies conducted with the aid of the telescope were also responsible for several important longitudinal determinations, as late as 1905. The telescope has been located on the rooftop of Crow Hall, home of the school's physics department, since 1954. Climbing the narrow stairs into the attic of the physics department and up the ladder onto the roof of the building is like entering a time machine. Don't be surprised if you bump into the ghost of H.G. Wells. The observatory is open from 7-10 p.m. Monday-Friday during the school year. Groups of seven or more or disabled persons should make advance reservations by calling 314-935-6250. To learn whether the observatory is open on a particular evening, call 314-935-6278.