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.