ISS Pass Predictor — Plus Starlink and Bright Satellites

ISS pass predictor: when and where to look for the Space Station

The International Space Station is the brightest artificial object in the sky — on a good pass it outshines every star and planet except Venus — but it is visible only for a few minutes, when it is sunlit while you are in darkness. This ISS pass predictor finds those moments for your location: when it rises, where from, how high it climbs, where it disappears and roughly how bright it will be.

Switch to Satellite group to make it a Starlink satellite tracker: it downloads CelesTrak’s space-station, brightest-satellite or Starlink list and finds every visible pass, grouping Starlink trains into one row. Predictions use the standard SGP4 orbital model through the open-source satellite.js library; the orbit maths, sunlight test and twilight check run in your browser, and your location is never transmitted.

How to use the ISS Pass Predictor

1. Choose your City, enter coordinates and time zone, or press Use my location.
2. Press Fetch latest TLE for the current ISS element set, or paste a TLE; the line under it shows the name, NORAD number and element age.
3. Set the Start date and time, how many Days ahead to search, and the Minimum peak elevation (10° is the usual threshold; 30°+ for the best passes).
4. Press Predict passes: the panel shows the next visible pass and the table lists them all.
5. For Starlink and other satellites choose Satellite group, pick a group and press Download group; the table then lists every visible pass for up to three days. All passes adds daytime and shadowed passes for radio operators.

ISS Pass Predictor features

How ISS visibility works

The Station orbits about 420 km up, circling the Earth every 93 minutes at 27 600 km/h, inclined 51.6° to the equator, so it can be seen from anywhere between about 60° N and 60° S. Most passes are invisible — in daylight, or in Earth’s shadow at midnight. Visible passes come in the hour or two after sunset and before sunrise, when you are in darkness but the Station is sunlit.

A pass lasts up to about six minutes. The Station crosses from one side of the sky to the other, or vanishes in mid-sky as it enters the shadow (a visible portion shorter than the pass). It never blinks. Peak elevation is what matters: a 10° pass hugs the horizon, a 40° pass is excellent, and an 85° pass goes almost overhead.

Starlink trains and other bright satellites

Newly launched Starlink satellites fly in a line — a “train” — at about 300 to 400 km while they raise their orbits, and are bright for a few days to weeks. In the Starlink group the predictor keeps only satellites below about 430 km (15.45 revolutions a day or more), where the trains are, and merges passes that start within three minutes on a similar track. At their final 550 km height they are usually magnitude 5 to 7. Group data comes from CelesTrak as CSV, because objects catalogued since July 2026 have six-digit numbers the TLE format cannot hold. As CelesTrak’s usage policy asks, each group is downloaded only on a button press, at most once every two hours, and requests stop for two hours after any error.

About the element set (TLE)

A two-line element set describes the orbit at one moment, its epoch. SGP4 extrapolates forwards, but drag and the Station’s engine burns make an element set age: predictions are good to a few seconds with elements a day or two old and drift by a minute or more after a week, which is why the TLE age is shown and the sample set is only for trying the page. The epoch is a two-digit year and a fractional day of year — the Julian date converter turns that into a calendar date.

Tips for a good sighting

• Go out early and face the “From” direction.
• Passes just after civil twilight ends (see the sun position calculator) are the brightest.
• Check the star chart and planets visible tonight so you do not mistake Venus or Jupiter for it.
• For photography, a 20–30 s exposure at ISO 800 with a wide lens records a bright streak.