A weird-looking old man with a telescope stands on a San Francisco street corner and urges passersby to "Come see the moon." Most keep walking, convinced he's either pitching or panhandling. Actually, he's John Dobson, the designer of a high-powered telescope that nearly anyone can make, using plans that Dobson eagerly shares. The former Buddhist monk calls himself "a sidewalk astronomer" in direct contrast to "a backyard astronomer," because he and his followers believe in amateur stargazing in public, where they can proselytize about the wonders of the universe. Dobson's been preaching about the sky since 1967, and has his patter down. Whenever someone stops to marvel at the images in Dobson's scope, he smiles beatifically and says, "Yes, the exterior decorator does lovely work."

Jeffrey Jacobs' slight-but-winning documentary A Sidewalk Astronomer skimps on Dobson's life story, though Dobson himself covers some of it as part of his regular stand-up routine. He was born in Peking to a family of prestigious British academics, and moved to San Francisco as a teenager in the '20s. Dobson became a devout atheist when he realized he couldn't reconcile the phrase "do unto others what you would have them do unto you" with the concept of Hell, but after hearing an inspiring lecture in the '40s, he abandoned his scientific studies in favor of monasticism. Then he abandoned the order for science in the '60s, after a consuming passion for telescope-making interfered with a regimen of meditation and prayer. Most of Dobson's subsequent life has been spent reconciling spirituality and logic, most famously in his lectures about the impossibility of the Big Bang theory.

Jacobs focuses almost exclusively on Dobson's theories and mission, which he illustrates by contrasting jaw-dropping images of the sun's surface with people ignoring Dobson's entreaties to "Come look at the sun." For the people who stop, though—and for those who attend Dobson's more formal workshops and classes—he holds court, employing easy-to-understand metaphors to make the cosmos sound wonderful and worthy. When people see something they haven't seen before, they respond with awed silence. But Dobson keeps talking, because he's seen it all, and can only experience it anew through the eyes of others. "Remember," he urges, "Everything we know about the universe has been observed by people as stupid as us."