What is an orbit?
An orbit is a fall that never lands. A satellite in low Earth orbit moves sideways at about 7.7 km per second — so fast that as gravity pulls it down, the Earth's surface curves away beneath it at the same rate. Isaac Newton described this thought experiment with a cannonball in 1687; today 20,000+ tracked objects do it for real.
The three main neighbourhoods
Low Earth orbit (LEO, 200–2,000 km) is home to the ISS and Starlink — one lap takes ~90 minutes. Medium Earth orbit (MEO, ~20,000 km) hosts GPS, Galileo and GLONASS, circling twice a day. Geostationary orbit (GEO, 35,786 km) matches Earth's rotation exactly, so satellites there hover over one spot — perfect for TV and weather.
How trackers know where everything is
Radars and telescopes measure each object's orbit, published as TLEs (two-line element sets) — a compact 1970s format still used today. An algorithm called SGP4 turns a TLE into a position at any moment, accurate to about a kilometre for days. Cosmik computes SGP4 live in your browser for the whole catalogue — nothing is pre-rendered.
Why orbits decay
Below ~500 km, wisps of atmosphere still exist. Each collision with an air molecule steals a little speed, the orbit shrinks, drag grows, and the object eventually re-enters — that's why the ISS needs regular boosts, and why old satellites end as bright artificial meteors.
Frequently asked questions
What keeps satellites in orbit?
Speed, not the absence of gravity. A satellite falls toward Earth continuously — but it moves sideways so fast (about 7.6 km/s in low orbit) that the ground curves away beneath it. Orbit is falling — and forever missing the ground.
How high do satellites orbit?
Three main neighborhoods: low Earth orbit (300-2,000 km — the ISS, Starlink), medium orbit (~20,000 km — GPS), and geostationary (35,786 km — where satellites hover over one spot). You can see all three layers on Cosmik's live 3D map.
Why don't satellites fall down?
The ones in low orbit actually do, slowly: thin air drags them down over years, which is why the ISS re-boosts monthly. Higher up there's essentially nothing to slow them — GPS satellites will outlast their builders by centuries.
Keep exploring
- How to track satellites live
- What happens when satellites fall
- ISS pass times over your city
- 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.
