ISS Orbit Tracking City Min

Estimating ISS Pass Duration from Maximum Elevation

The International Space Station sits at roughly 400 km altitude, lapping the planet every 90 minutes or so at nearly 7.66 km/s. From your city it shows up as a bright dot crossing the sky, and the whole thing is over in a handful of minutes. To get a rough sense of how long a pass lasts, this calculator uses duration = elevation ÷ 15. Here elevation is the highest angle above the horizon the station reaches during the pass, in degrees, and you get the answer back in minutes.

It comes down to geometry. A high pass that goes nearly overhead (close to 90°) keeps the ISS above the horizon longer, so it runs about 4–6 minutes. A low pass that barely clears the horizon (10–20°) is gone in a minute or two. Proper predictions from NASA Spot The Station or Heavens-Above go further, weighing orbital geometry, your latitude and whether the station is catching sunlight, so think of this number as a planning estimate rather than an exact ephemeris.

Applications

Plan a viewing session with it. If a pass peaks at 70°, you can count on roughly 4.7 minutes of visibility, which is enough to get a camera ready or show the station to friends. It also helps with astronomy outreach, with deciding whether a pass is worth staying up for, and with teaching how pass altitude ties into the visibility window.

FAQ

Why does a higher pass last longer? When a pass climbs to a high elevation, it traces a longer arc of sky above your local horizon. That means the station stays in view through more of its orbit before it sets.

Is the divide-by-15 formula exact? No, it is a linear approximation. Real visibility also hangs on how the orbit is angled against your sky and on lighting conditions, so lean on dedicated tracking sites when you need precise rise and set times.

Can I see the ISS during the day? Usually not. Your best bets come shortly after dusk or just before dawn, when your sky has gone dark but the station up there is still lit by the Sun.