How to spot the International Space Station and other bright satellites with your naked eye.
When you see the ISS cross the sky, you're watching a 109-metre structure — the size of a football pitch — orbiting at 408km altitude and moving at 27,600 km/h. It's not producing its own light. What you see is sunlight reflecting off its massive solar arrays, which act like enormous mirrors.
This is why satellite passes only happen during specific windows: the satellite needs to be in sunlight while your sky is dark. During the middle of the night, satellites are in Earth's shadow and invisible. The geometry only works during the hours around dusk and dawn, when the sun is below your horizon but still illuminating objects at orbital altitude.
The ISS is by far the brightest satellite in orbit. At its best, it reaches magnitude −4 or brighter — comparable to Venus — making it one of the most brilliant objects in the night sky. It's unmistakable: a steady, bright point of light moving smoothly from west to east, crossing the entire sky in 3–5 minutes. Unlike aircraft, it has no flashing lights. Unlike stars, it moves in a smooth, continuous arc.
Satellite passes are only visible during a specific time window determined by the geometry of sun, satellite, and observer. For the ISS, this typically means the first few hours after sunset and the last few hours before sunrise.
In winter, when nights are long and the sun drops well below the horizon, the visibility window is narrow — perhaps 1–2 hours after dusk and before dawn. During the long twilight of summer, the window expands dramatically. From the UK in June, the ISS can be visible for most of the night because the sun never drops far enough below the horizon for the ISS to enter Earth's shadow. This is why summer is the peak season for satellite watching — you can see multiple ISS passes in a single evening.
The ISS orbits Earth every 90 minutes, but it's not always visible from your location on each pass. The orbit track shifts slightly with each revolution, so some passes are overhead (bright and long), some graze the horizon (faint and brief), and some miss your visible sky entirely. A typical location gets 2–6 good passes per week during a visible window, with none during the off-season between windows.
Clear Skys computes all visible passes for your location and shows them in the forecast. Each pass includes the start time, direction, maximum altitude (how high it gets in the sky), brightness, and duration. Only passes bright enough to be easily visible (typically magnitude 0 or brighter for the ISS) are shown.
Watching a satellite pass requires no equipment — just your eyes, a clear horizon in the right direction, and the right timing. Here's the practical approach.
Know the direction. Each pass has a start direction (where the satellite first appears) and an end direction (where it disappears or fades). The ISS almost always appears somewhere in the west and travels broadly eastward. Clear Skys shows the start and end compass bearings — face the start direction a minute or two before the predicted time.
Understand altitude. A pass reaching 70° altitude goes almost directly overhead — that's the most spectacular view. A pass reaching 20° altitude stays low on the horizon and is fainter because you're seeing it through more atmosphere. Anything above 40° is a good pass worth watching.
Watch for shadow entry. On evening passes, the ISS sometimes enters Earth's shadow mid-transit. You'll see the bright point smoothly fade to nothing over a few seconds — it's like watching the satellite being switched off. This happens because the ISS has moved into the cone of darkness behind Earth. It's one of the more visually striking things you can see with the naked eye.
Time accuracy matters. Satellite pass predictions are precise to within a few seconds. If the pass is predicted at 22:14, look up at 22:13 — don't wait until 22:20 and hope to catch it. A low, fast pass might be visible for under 90 seconds.
The ISS isn't the only satellite visible to the naked eye. Clear Skys tracks approximately 20 reliably bright satellites using TLE (Two-Line Element) data from Celestrak, refreshed every 12 hours. Here are the most notable.
**Tiangong (Chinese Space Station)** is the second-brightest crewed spacecraft in orbit. It's smaller than the ISS but still reaches magnitude −2 to −3 during good passes — easily visible even from light-polluted cities. It orbits at a similar altitude to the ISS (about 390km) but on a different orbital inclination, so its visibility windows don't coincide.
**Hubble Space Telescope** orbits at around 540km and can reach magnitude +1 to +2 during favourable passes — fainter than the ISS but still visible to the naked eye in clear conditions. Its higher orbit means it catches sunlight for longer after sunset.
**Starlink trains** are the most commonly reported satellite sightings in recent years. Newly launched Starlink satellites initially orbit in a close "train" formation, appearing as a string of evenly spaced dots moving across the sky. They're visually striking but become fainter as they spread out and raise their orbits over the following weeks.
Any pass listed in your Clear Skys forecast is predicted to be bright enough to see without binoculars or a telescope. Fainter passes and debris are filtered out — you only see what's worth going outside for.
Summer is far and away the best season for satellite watching in the UK and northern latitudes. The reason is the same phenomenon that makes summer bad for deep-sky stargazing: the sun never drops very far below the horizon.
For a satellite at 400km altitude, the sun is still visible even when it's 20° or more below your horizon. During the UK's midsummer, when the sun barely reaches 12–16° below, satellites remain illuminated for most or all of the short night. In June from London, you can see ISS passes from 10pm through to 3am on the same night.
In winter, the deep darkness means the illumination geometry only works for a brief window around dusk and dawn. You might get one or two passes per evening, and none in the middle of the night.
This makes satellite watching an excellent activity for summer nights when traditional stargazing is limited by twilight. You can't see the Milky Way in June from the UK, but you can watch the ISS glide overhead three times in one evening.
Clear Skys shows all visible bright satellite passes for your location in tonight's forecast. Each pass includes timing, direction, altitude, brightness, and duration. Search your location or check one of these forecasts:
Check tonight's stargazing conditions for any location worldwide.
Search your location →Pass times depend on your location and change daily. Check your Clear Skys forecast — it lists every visible ISS pass for the next few nights with exact timing, direction, and brightness. The ISS is only visible during a window around dusk and dawn when the station is sunlit but your sky is dark.
The ISS regularly reaches magnitude −3 to −4, making it one of the brightest objects in the sky — comparable to Venus at its best. It's unmistakable: a steady, brilliant point of light moving smoothly across the sky in 3–5 minutes, with no flashing lights.
No. The ISS and other bright satellites listed in Clear Skys are all naked-eye objects. In fact, a telescope makes them harder to follow because they move too fast for a narrow field of view. Just look up at the right time and direction.
That's almost certainly a Starlink satellite train. Newly launched Starlink satellites orbit in a close formation that appears as a line of evenly spaced dots. They spread out and dim over the following weeks as they raise their orbits to their operational altitude.