ISS Tracker: spot the Space Station tonight
The International Space Station (ISS) is the brightest man-made object in the sky — sometimes brighter than Venus. Yet many people don't know what they're looking at when they see it. Sky Lens calculates exact pass times and positions for your location.
The ISS is uniquely recognisable — once you know what to look for. No other object combines this brightness, speed, and behaviour.
Brightness
Magnitude up to -4 under favourable geometry — brighter than Venus, all planets, and all stars. Only the Moon and Sun outshine it. Average magnitude -1 to -3 during a typical pass.
Colour and light character
Bright white. No flicker — completely steady, constant light. This immediately distinguishes it from aircraft (which have strobes) and stars low on the horizon (which scintillate).
Speed
Crosses the sky from horizon to horizon in 3–5 minutes depending on the maximum elevation above your location. Noticeably faster than a cruising airliner, slower than a meteor.
Sound
Completely silent. The ISS orbits at 408 km altitude — any sound is entirely inaudible from the ground. If you can hear anything at all, it is an aircraft, helicopter, or drone. The ISS is always silent.
Direction
Moves generally west to east or southwest to northeast, depending on the orbit at that moment. The ISS has an orbital inclination of 51.6° — it never passes directly over the polar regions.
Fade-out
The ISS can gradually dim and disappear as it enters Earth's shadow — a slow fade from bright white to nothing while it is still high overhead. This is spectacular and characteristic of satellites.
The ISS is not visible every evening or morning. Visibility depends on the geometry between the station, the Sun, and your location on Earth.
Twilight required
The ISS is only visible when it is in sunlight while your ground location is already in shadow. This gives a visibility window in the first 1–2 hours after sunset or the hours before sunrise. In the middle of the night the station enters Earth's shadow and becomes invisible.
15–16 orbits per day
The ISS completes one full orbit every ~90 minutes. Over a day there are multiple passes overhead, but most fall during daylight or the middle of the night. The visible evening and morning passes shift in path and time each day.
Seasonal variation
In summer the ISS can sometimes be seen late in the evening because the sun has only recently set. In winter the windows are shorter but the sky is darker — ideal for observation.
Maximum elevation determines brightness
A pass almost directly overhead (maximum elevation ~90°) gives a much brighter and longer sighting than a pass low on the horizon. Sky Lens shows the maximum elevation for each pass so you know in advance how spectacular it will be.
The ISS and a cruising airliner can look confusingly similar. Here are the decisive differences.
No navigation strobe
Aircraft are legally required to carry strobes that flash every 1–2 seconds. The ISS has no visible light sources of its own — it only reflects sunlight. If there is no strobe pattern, it is not an aircraft.
Constant speed and direction
The ISS follows a perfect arc across the sky — no turns, no acceleration, no variation. Aircraft sometimes change course or speed. The ISS also never appears to slow as it approaches.
Fades gradually into shadow
When the ISS enters Earth's shadow it dims slowly — from bright white to progressively fainter over 30–60 seconds. Aircraft never do this — they simply fly away beyond the horizon or become obscured by cloud.
Use a fixed reference point
When watching a bright point against a dark sky it can seem to move even when it is stationary — this is the autokinetic effect. Always use a fixed reference (roofline, chimney, aerial) to distinguish real movement from visual illusion.
Completely silent
The ISS produces no audible sound from the ground — it orbits at 408 km. If you hear anything at all, it is an aircraft, helicopter, or drone. The ISS is always completely silent.
Sky Lens has current TLE orbital data for the ISS, updated multiple times per day. Calculations are accurate to seconds and arc-minutes.
Precise position calculation
Via the Skyfield library and current TLE data, Sky Lens calculates the exact position of the ISS at any requested time. The calculation accounts for the sub-point track, orbital inclination, and Keplerian corrections.
Elevation angle and azimuth
For your location and time, Sky Lens determines at what elevation angle the ISS was positioned, in which direction it was moving (azimuth at maximum elevation), and how bright it was based on distance and solar geometry.
Candidate list
If the ISS matches your description (direction, elevation, time, brightness), it appears at the top of the probability list — with the calculated parameters as supporting evidence. You can see exactly what angle and direction Sky Lens calculated.
Enter your location and the time. Sky Lens calculates whether the ISS was overhead at that moment — and gives you the exact elevation angle, direction, and brightness.