Why do satellites blink at night?
Satellites don't blink the way planes do — they carry no lights you can see from the ground. What you're seeing is reflected sunlight, and when a satellite appears to pulse or flash, it's because the object is tumbling: flat surfaces like solar panels catch the Sun at a changing angle with every rotation, like a slow-motion mirror ball.
Steady light vs blinking light
A steady, non-blinking point gliding across the sky is usually an active, attitude-controlled satellite — the ISS is the brightest example. A rhythmic flasher is typically a spent rocket stage or a dead satellite spinning end over end. Time the flashes and you're literally measuring its rotation period from your garden.
Flares: the brightest blinks of all
When a large flat panel swings through exactly the right angle, it can throw a concentrated beam of sunlight at your location — a flare that briefly outshines every star. The old Iridium satellites were famous for predictable flares; today's giant flat-panel Starlink satellites produce their own glints, especially in the days after launch.
And when it vanishes mid-sky?
That's not blinking — that's Earth's shadow. A satellite stays visible only while sunlight reaches it; when its orbit carries it into the planet's shadow cone, it fades out in seconds, often directly overhead. Cosmik's live map predicts the exact shadow-crossing point for every pass.
Frequently asked questions
Do satellites have lights?
No — nothing you can see from the ground. Every satellite you spot is reflecting sunlight, like a tiny fast-moving mirror. That's why they're visible only when you're in darkness while the satellite, high above, is still in sunshine.
Why does a satellite seem to flash or blink?
It's tumbling. Flat surfaces — solar panels, antennas — catch the Sun at changing angles as the satellite rotates, so brightness pulses. A steady non-blinking mover is usually an active, stabilized satellite; a rhythmic flasher is often a spent rocket stage or dead satellite spinning.
How do I tell a satellite from a plane?
Planes blink with colored strobes and move relatively slowly; satellites are a single steady (or slowly pulsing) white point crossing the whole sky in 2-6 minutes, always in the hours after sunset or before dawn. If it suddenly fades mid-sky, it just entered Earth's shadow — a satellite giveaway.
Keep exploring
- Can you see satellites in daylight?
- When does the ISS pass over your city?
- The Starlink train, explained
- All space explainers
See it yourself tonight
Theory is better with a sky. Get the next ISS pass times over New York, London, Paris, Tokyo, Berlin or Sydney — or any of 550+ cities. Aurora hunter? Check tonight's forecast for your city.
