ISS Tracker
Spotting the International Space Station overhead.
Overview
The International Space Station orbits Earth roughly every 90 minutes at about 400 kilometres altitude, and during favourable passes it is one of the brightest objects in the sky — a steady, fast-moving point that crosses from horizon to horizon in a few minutes.
- The ISS shines by reflected sunlight, so it is only visible when it is sunlit and you are in darkness.
- That restricts sightings to roughly the couple of hours after sunset and before sunrise.
- It moves steadily and does not blink — aircraft blink, satellites do not.
- A pass that fades out mid-sky is the station entering Earth's shadow.
Why passes only happen at twilight
The ISS produces no visible light of its own; it reflects sunlight from its large solar arrays and structure. To see it you need two conditions at once: the station must be in sunlight, and your location must be dark enough for it to stand out.
That combination only occurs when the Sun is below your horizon but still illuminating objects a few hundred kilometres up — roughly the first couple of hours after sunset and the last couple before sunrise. In the middle of the night the station passes through Earth's shadow and is invisible even when directly overhead.
What a pass looks like
The station appears as a steady white point, comparable to or brighter than the brightest stars, moving noticeably against the background — fast enough that motion is obvious within a second or two, but far slower than a meteor. A typical visible pass lasts around two to six minutes from horizon to horizon.
It does not blink or flash. Aircraft carry flashing navigation lights; the ISS does not, and that is the quickest way to tell them apart. Passes often end with the station fading out partway across the sky rather than setting — that is the moment it crosses into Earth's shadow.
Getting accurate predictions
Pass times depend on your precise location and on the station's current orbit, which changes: atmospheric drag lowers it continuously and periodic reboosts raise it again, so predictions made from old orbital elements degrade within days.
Accurate prediction therefore requires current two-line element sets from an authoritative source such as NORAD via CelesTrak, propagated with an appropriate orbital model. Asteria Star does not publish invented pass times; where a prediction cannot be computed from current elements, the page says so rather than showing a plausible-looking figure.
Other satellites
Thousands of satellites are bright enough to see under dark skies, and on a clear night away from light pollution you will notice several within an hour. Most are far fainter and slower-looking than the ISS because they are smaller and often higher.
Large satellite constellations have made this substantially more noticeable, particularly shortly after launch when spacecraft are still clustered in a visible train. That same visibility is a genuine problem for astronomy: satellite trails contaminate long exposures, and the effect scales with the number of objects in orbit.
Continue in the data
Catalogues, hubs, and reference pages that hold the underlying records for this topic.
Frequently asked
- When can I see the ISS?
- During the couple of hours after sunset or before sunrise, when the station is still in sunlight but your sky is dark. In the middle of the night it passes through Earth's shadow and reflects nothing, so it is invisible regardless of how favourably it passes overhead.
- How do I tell the ISS from an aircraft?
- The ISS is a steady white point with no flashing. Aircraft carry blinking navigation lights and usually show more than one colour. The station also crosses a large arc of sky in a few minutes at a constant rate, and frequently fades out mid-pass when it enters Earth's shadow — something an aircraft never does.
- Why do pass predictions need updating?
- Because the station's orbit changes. Atmospheric drag lowers it continuously, and periodic reboosts raise it again, so orbital elements go stale within days. Accurate predictions require current element sets from an authoritative tracking source, propagated with a suitable orbital model.