Steady Light Gliding Across the Sky? Satellites and the ISS Explained
A star-like point of light that glides smoothly and silently across the sky over a few minutes is usually a satellite. They shine by reflecting sunlight, so they are seen after dusk and before dawn. The International Space Station is the brightest of all, often outshining every star.
What it looks like
- A single steady point of light, with no blinking or coloured lights.
- Moving in a straight line at a constant speed, crossing much of the sky in a few minutes.
- Silent.
- Sometimes fading out or disappearing suddenly while still high up, as it enters Earth’s shadow.
- The ISS is very bright and can take up to about six minutes to cross.
How to check
- Run our sky checker for the time and place; it calculates real satellite and space station passes.
- Note which way it was travelling and how high it got: these are what distinguish one pass from another.
- If it blinked or you heard engines, it was more likely an aircraft.
Questions
Why did the light just disappear?
Satellites are lit by the Sun. When one moves into Earth’s shadow it stops reflecting sunlight and seems to vanish, even though it is still there.
How bright is the ISS?
At its best the International Space Station is brighter than any star and only fainter than the Moon and Venus.