Calculate when the International Space Station will be visible from your location.
The International Space Station circles Earth every 92 minutes at about 7.66 km/s, and at its best it is the brightest moving object in the night sky - brighter than any star. Give this tool your location and it predicts the passes ahead: when to go outside, how high the station will climb, which direction to look, and how bright it will be. The one thing that surprises nearly everyone: the ISS is not visible every night, and each pass lasts only a few minutes.
The station's orbit is described by a snapshot of its position and motion, called orbital elements. Propagating those elements forward produces the ground track - where the station will be at every moment. A pass is any interval in which that track rises above a minimum elevation above your horizon. The tool then keeps only the passes where the station is lit by the sun while your sky is dark enough to see it.
Whether a pass is visible depends on the beta angle - the angle between the station's orbital plane and the sun. When the angle is small, the station dips into Earth's shadow each orbit, so visible passes are brief and low, near dawn and dusk. When it is large, the station stays sunlit for whole orbits and can sail overhead after dark. The angle cycles over about two months, so passes arrive in runs of nights, then a lull.
That is normal, not an error. ISS visibility runs in cycles set by the beta angle - the tilt between the station's orbit and the sun. When the geometry keeps the station in Earth's shadow during your night, nothing is visible. A week or two later the angle shifts and passes return, sometimes two or three in one night.
Almost certainly. The ISS takes four to six minutes to cross the sky, shows a steady light, and makes no sound, while aircraft blink, linger, and can turn. If the time and direction match a predicted pass from your location, that confirms it. A handful of other satellites are nearly as bright, but the ISS is by far the most common explanation.
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