Satellite Pass Predictions — How to Find Passes

Satellite pass predictions tell you exactly when a satellite will be visible from your location — the time it appears, its direction, how high it climbs in the sky, and how bright it will be. These predictions are generated by propagating orbital elements (TLE data) forward in time and computing the geometric relationship between the satellite, the Sun, and your position on Earth.

Understanding Pass Details

Elevation (Altitude Angle)

Measured in degrees from the horizon (0°) to directly overhead (90°). Passes above 40° elevation are considered good — the satellite is high enough to be well-lit and clearly visible. Passes below 10° are usually lost in the atmospheric haze near the horizon.

Magnitude (Brightness)

Uses the astronomical magnitude scale. Lower numbers mean brighter objects. The ISS on a good pass can reach –3.5 (brighter than any star). A magnitude 4 satellite is faint but visible in dark skies. Anything above magnitude 6 requires binoculars.

Direction

Passes list a start direction and end direction using compass bearings or cardinal directions (NW, SE, etc.). The satellite rises from one horizon and sets at the other, tracing an arc across the sky.

Duration

A typical visible pass lasts 2–6 minutes. The satellite may "disappear" mid-pass if it enters Earth's shadow — this is normal and simply means the sunlight can no longer reach it.

How Predictions Are Made

All tracked satellites have published orbital elements — two-line element sets (TLEs) — that describe their current orbit. By applying physics-based propagation models (SGP4), the future position of the satellite can be calculated to high accuracy.

A pass occurs when the satellite's propagated position is above the observer's horizon and the satellite is illuminated by the Sun while the observer's sky is dark. The prediction combines these geometric conditions to identify all visible passes for a given location.

ℹ️ How Orbital Radar Calculates Passes

Orbital Radar uses regularly-updated TLE data and the SGP4 propagation model to compute pass predictions. The Sat Pass tool in the left menu takes your location (entered or geolocated) and returns upcoming visible passes with time, direction, elevation, and estimated brightness.

Tips for Best Results

Prioritise high-elevation passes. A pass reaching 60°+ elevation is brighter, lasts longer, and is easier to follow than a low-skimming pass at 15°.

Check magnitude. If a pass is listed as magnitude 3 or fainter and you are in a light-polluted area, it may be difficult to see. Aim for magnitude 1 or brighter for urban locations.

Give yourself a margin. Predictions are highly accurate but not perfect. Arrive a few minutes early and scan the predicted start direction. The satellite may appear slightly earlier or later than listed.

Frequently Asked Questions

With recently-updated TLEs, predictions are typically accurate to within a few seconds for time and a degree or two for position. Accuracy degrades over days as atmospheric drag and other perturbations cause the orbit to drift from the prediction.

Visible passes require a specific geometry — dark sky for the observer, sunlit satellite. Depending on the satellite's orbit and the season, there can be gaps of a week or more between visible pass windows for a given location.