When the government announced last month that a top-secret spy satellite would, in the next few months, come falling out of the sky, American officials said there was little risk to people because satellites fall out of orbit fairly frequently and much of the planet is covered by oceans.

But they said precious little about the satellite itself.

Such information came instead from Ted Molczan, a hobbyist who tracks satellites from his apartment balcony in Toronto, and fellow satellite spotters around the world. They have grudgingly become accustomed to being seen as “propeller-headed geeks” who “poke their finger in the eye” of the government’s satellite spymasters, Mr. Molczan said, taking no offense. “I have a sense of humor,” he said.

Mr. Molczan, a private energy conservation consultant, is the best known of the satellite spotters who, needing little more than a pair of binoculars, a stop watch and star charts, uncover some of the deepest of the government’s expensive secrets and share them on the Internet.

Thousands of people form the spotter community. Many look for historical relics of the early space age, working from publicly available orbital information. Others watch for phenomena like the distinctive flare of sunlight glinting off bright solar panels of some telephone satellites. Still others are drawn to the secretive world of spy satellites, with about a dozen hobbyists who do most of the observing, Mr. Molczan said.