Questions

Frequently asked questions

The questions that come up most often about the station, the tracker and what you can actually see from the ground.

Is the ISS visible every night?

No. You need the station above your horizon while you are in darkness and it is still in sunlight. Those conditions come in clusters of roughly one to two weeks of evening passes, then a gap of a week or more, then a run of morning passes.

Why does it suddenly disappear in the middle of a pass?

It enters Earth's shadow. The station is only visible because it reflects sunlight; once it is in the shadow cone it stops reflecting and fades out within seconds. Nothing is wrong and it has not been switched off.

How fast does the ISS actually travel?

About 7.66 km/s, or roughly 27,600 km/h. That is one orbit every 92 to 93 minutes. Over Europe a single pass typically takes three to six minutes from horizon to horizon.

Do I need a telescope or binoculars?

No. The ISS is bright enough to see easily with the naked eye on a decent pass. Binoculars show it as a small elongated shape rather than a point, but they narrow your field of view and make it harder to follow. Naked eye is the best way to start.

Why does the map show a different location than my city?

The globe shows the sub-satellite point — the spot on Earth directly beneath the station — and the ground track, not your own position. The station is usually hundreds of kilometres away horizontally even when it appears overhead.

Where does the position data come from?

Two-line element sets (TLEs) published by CelesTrak, propagated with standard SGP4 orbital mechanics. The image itself is rendered by xplanet from the current sub-point. TLEs are refreshed regularly because atmospheric drag changes the orbit continuously.

What is the difference between the ISS and Tiangong?

Both are crewed stations in low Earth orbit. The ISS is about four times more massive, is inclined at 51.6°, and is much brighter. Tiangong is inclined at 41.5°, so from northern Europe it stays low in the southern sky and is dimmer. See the Tiangong page for the comparison.

Is this site really free?

Yes. There is no account, no subscription and no paywall. Hosting is paid for by advertising. The tracker itself does not require JavaScript frameworks or a login.

Can I use the images on my own site?

The rendered frames are generated from public orbital data, but please do not hotlink or redistribute them in bulk. Ask first — see terms.