The first known telescope was built almost 400 years ago, in 1608. When Italian astronomer Galileo Galilei presented a telescope to the Doge of Venice in August 1609, it was about as powerful as a modern field glass.

In December of that same year, Galileo assembled a telescope that was 20 times more powerful. Looking through his new instrument took him on a visual journey to places no one had gone before: He saw mountains and craters on the moon. He found that the Milky Way is composed of stars, and he discovered the four largest satellites of Jupiter.

The field of astronomy has traditionally been limited to scientists with access to expensive equipment. Only since the late 1960s has "astronomy for the masses" really gained popularity.

John Dobson with his students.

Sidewalk Astronomers member Ray Cash says Dobson, whom he describes as "an 85-year-old, kind hippie," founded the group in the late 1960s. Several of the students in Dobson's telescope-making class were disappointed when a local astronomy club rejected their membership. The reason: they were younger than the required 18 years of age.

Dobson was known for dragging his telescope out to the sidewalks of San Francisco and allowing people to look over his shoulder. Dobson wanted to reach out to everyone. Cash says the Sidewalk Astronomers still have a "take to the streets" approach.

"We'll set up on a corner, and get our share of drunks as well as generally curious people," he said. "It's very rewarding."

Cash says Dobson has always wanted to wreck the "rich man's club" that has dominated astronomy.

"He wants to teach people how to do it economically, and he feels that by looking at the sky, it will transform you," Cash said. "He sees it as a spiritual thing."

Dobson also designed a telescope for the masses. After reading an article in Smithsonian magazine more than three decades ago, he created in his basement a prototype telescope for the amateur astronomer using salvaged Navy glass and a couple of plywood boxes with a lazy Susan-type mount. Today, several telescope manufacturers produce Dobsonians, which are good-quality, affordable beginner telescopes (priced at about $400).