Satellites and the ISS: spotting moving lights
How to tell satellites from planes and meteors, when the ISS is visible and why satellites vanish mid-sky.
On any dark evening you can see a satellite every few minutes: a steady point of light gliding across the stars.
Satellite, plane or meteor?
- Satellite: steady, no blinking lights, crosses the sky in a few minutes, silent.
- Plane: red and green navigation lights and a white strobe that blinks.
- Meteor: a streak that lasts a second or less.
Why they appear and disappear
Satellites shine only by reflecting sunlight. You see them in the first hours after sunset and before sunrise, when the sky above you is dark but the satellite, hundreds of kilometres up, is still in sunshine. A satellite that fades out halfway across the sky has just entered Earth’s shadow.
The ISS
The International Space Station is about the size of a football pitch and orbits at roughly 420 km, circling Earth every 92 minutes. It outshines everything except the Moon and Venus. A good pass lasts 4–6 minutes and climbs high in the sky. The ISS page lists visible passes for your place.
Starlink trains
Right after launch, Starlink satellites travel in a tight line, a spectacular sight for a few days. Later they spread out and dim. They also brighten the sky’s background for astronomers, which is why satellite brightness is now an active topic of research.