Roughly 11,000 active satellites orbit the Earth today, and the number has more than doubled in a few years. Communications satellites make up over half of them; then come Earth-observation satellites, technology demonstrators and the navigation satellites this site is built around.
Turn on every layer above and you are looking at all of them at once. Turn on only GNSS and about 120 remain: the satellites that make positioning work.
They are falling. Throw something sideways and it traces an arc to the ground; throw it fast enough and the ground curves away beneath it just as fast, so it never arrives. That is an orbit.
At around 400 km the required speed is about 7.7 km per second, which is one lap of the planet every 90 minutes. Watch the space station in the panel and you will see it cross the globe in that time.
Low orbit, 200 to 2,000 km: observation, the space station, internet constellations. Ninety minutes to two hours per lap.
Medium orbit, around 20,000 km: navigation. High enough to be seen from a wide area, low enough for the signal to stay strong. GPS takes about twelve hours per lap.
Geostationary orbit, 35,786 km: weather and broadcasting. At that height one lap takes exactly 24 hours, so the satellite appears to hang still above one point. That is why a satellite dish never moves.
Switch on QZSS and watch its path. It draws a figure of eight rather than a simple ring.
The orbit is tilted and shaped so that the satellite spends far longer over the northern half of its track than the southern. From Japan it stays near the zenith for about eight hours a day, and three satellites in sequence keep one of them almost overhead around the clock.
Being overhead matters. In a city, low satellites are hidden behind buildings; only the one directly above is never blocked.
Satellites are visible without a telescope, but they do not shine. They reflect sunlight, so the sky where you stand must be dark while the satellite above is still lit. That happens for about an hour and a half after sunset and before sunrise.
They are often mistaken for aircraft. Aircraft blink red and green; a satellite is a steady point that crosses the sky at an even pace and frequently vanishes mid-flight as it enters the Earth's shadow.
The brightest is the space station, which at a good pass rivals Venus and is easy to see from a city.
Every satellite here is drawn from published orbital elements and propagated with the standard SGP4 model. Nothing is invented; the elements are updated regularly, and an old set drifts further from reality the longer it goes unrefreshed.
That is also why a satellite you click shows its NORAD number: it is the identity under which the element set is published, so anyone can check the same object against the same source.
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