The International Space Station (ISS) is a big bird, boasting nearly an acre of solar panels along its backbone. Those panels make the ISS reflective enough so that the station can sometimes be seen from the ground as it passes roughly 220 miles (350 kilometers) above. But where and when to look?

Enter Twisst, a new service that alerts space buffs on Twitter when the ISS is passing overhead. The service combines location information from a user's Twitter profile with data from Heavens Above, an online repository of satellite and spacecraft orbital information. (Twisst's co-creator, Govert Schilling, is an occasional freelance contributor to Scientific American.)

Based on those data, Twisst sends subscribers customized tweets with the time that the space station will become visible from their location. (Each pass brings the ISS into view for just a few minutes.) A link then provides more detailed information on how bright the ISS will be and where in the sky to look.

The service has experienced a few glitches since its launch—running up against Twitter's rate limit, Twisst has not been able to update all of its users on the ISS's whereabouts. And the first notice received by this reporter, at 5:51 A.M. on Saturday, appears to have arrived more than three hours after the event it heralded.

Twisst joins a robust line of space-faring bodies on Twitter—including the now-defunct Phoenix Mars lander, which amassed more than 45,000 followers on Twitter, and a pair of tweeting astronauts, one of whom posted updates to Twitter from orbit during a May space shuttle mission. And starting July 16, the Smithsonian National Air and Space Museum will honor the 40th anniversary of Apollo 11 by rolling out a sort of highlight reel on Twitter that aligns with the dates and times of the original 1969 mission.

Photo of the International Space Station against the curvature of the Earth: NASA