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Satellite Orbits

Why is the ISS round again in 90 minutes, while a TV dish never moves?

The ISS's orbit, drawn to scale round the globe, with polar, GPS and geostationary orbits: why each takes as long as it does, and where the geostationary belt sits in your sky.

You’ll be able to say why the ISS is round again in an hour and a half, and point to the geostationary belt.

8 steps · about 6 min

Before this: Satellites and the ISS (6 min)

Where and which night

Working out when this is best placed from where you are…

Where

Which night

Date

Time

Kept for this guide only, until you change it here — your map settings, and every other guide, stay as they are.

Print, play outside or present

Present on a big screen

Scan with a phone's camera, or open

Sources

Wikipedia, International Space Station — about 420 km up, at an inclination of 51.64°
NASA, Spot the Station FAQ — the station circles the Earth about every 90 minutes and travels about 28,000 km/h (17,500 mph)
USGS, Landsat 9 — a near-polar, Sun-synchronous orbit 705 km up, crossing the equator at 10:00 a.m. ± 15 minutes
GPS.gov, Space Segment — about 20,200 km up, each satellite circling the Earth twice a day, in six orbital planes
Wikipedia, Geostationary orbit — 35,786 km above the equator, one orbit per sidereal day; antennas can stay fixed on one point
NGA, World Geodetic System 1984 (TR8350.2) — GM = 398,600.4418 km³/s² and the Earth's equatorial radius, 6,378.137 km

← GUIDES

More below ↓

With a keyboard, focus the sky, aim it with the up and down arrow keys, and press Enter to drop the pin at the centre of the view; or press Show me.

You are here

Settings

Screen

Night mode Turns every page red, to keep your eyes adjusted to the dark.

High contrast Bolder constellation lines, larger and brighter names on the sky, and stronger text and edges everywhere. Starts on if your device asks for more contrast.

Reduce motion The camera cuts to where it is going instead of flying there, and panels and sheets appear without sliding. Starts on if your device asks for less motion.

Battery saver Draws the sky thirty times a second at most: smoothness traded for battery.

Night brightness Dims the screen below your phone’s lowest setting, down to a fifth, while night mode is on.

Clock and voice

Clock How every time is written. Until you choose, your language’s own clock decides.

D describes What D says about the view on the sky: one sentence, or in full with the field, the constellation and five names.

Sounds Quiet tones as you use the map: a tick as you drag the clock past a mark or dusk, a chime for the star you pick — higher for hotter stars — and a low swell while a figure is out of the dome. Made in your browser, and off until you turn them on.

All settings and your progress

Four satellite orbits round the globe, drawn to scale with it, each with a dot for its satellite. One of them carries the ISS, the brightest satellite in your sky.

The inner ring: the ISS, 420 km up, a sixteenth of the Earth's radius. Run one lap: 93 minutes at 28,000 km/h, 15 laps a day. The globe turns 23° under it meanwhile, so each pass crosses a new strip of ground.

Side-on to the equator, the ISS's ring is tilted 51.6° to the equator: the latitude of its launch site at Baikonur. The station never flies over ground farther north or south than that, so the farther from it you live, the lower its passes.

The ring over the poles is a polar orbit, 705 km up, where Landsat photographs the Earth. Run a day: the globe turns under it, so it sees every place in turn, and the ring holds its angle to the Sun, so it passes over each at the same time of day.

Farther out, 20,200 km up, the middle ring is GPS: one lap every 12 hours, twice a day. Two dozen satellites share six such rings, so your phone always has four or more above the horizon.

The outer ring, 35,786 km over the equator, is geostationary: one lap takes exactly one turn of the Earth. Run half a day: the ISS laps 8 times, and the outer satellite stays over the same spot.

Back on the ground, facing south. The dashed arc is the geostationary belt, home of every geostationary satellite; past about 81° of latitude it never rises. Run three hours: the stars trail past and the belt holds still, so a TV dish is bolted in place.

The geostationary belt, where your dish points.

The ISS laps the Earth every 93 minutes
Its tilted ring stays within 51.6° of the equator
Geostationary keeps pace with the Earth's turn