LEO Satellite Visibility Window

Predict how long a low-Earth-orbit satellite will remain above your minimum elevation threshold. The model assumes a circular pass, then scales the visible window for twilight so you can time ISS flyovers, Starlink trains, or imaging sessions.

Circular-orbit altitude above Earth's mean radius in kilometres.
Lowest elevation angle (degrees) you are willing to observe above the horizon.
Optional Sun altitude in degrees; -12° approximates nautical twilight and 0° indicates sunrise/sunset.

Examples

  • Starlink shell at 550 km with a 30° elevation cutoff during nautical dusk ⇒ 3.22 minutes
  • International Space Station near dawn with a 15° limit and Sun at −4° ⇒ 3.10 minutes

FAQ

Do I need current TLE data for this estimate?

Detailed predictions require up-to-date TLEs. This calculator offers a planning baseline using the altitude you supply to approximate the pass duration.

Why does daylight shorten the visibility time?

Bright twilight or daylight washes out all but the brightest satellites. The daylight factor scales the geometric window so the reported time reflects what is realistically visible.

Can I set the minimum elevation higher than 60°?

Yes, but expect very short windows. Near-zenith tracking leaves only a brief segment of the pass within your elevation constraint.

Additional Information

  • Geometry is Keplerian and assumes a circular pass; Earth rotation is negligible over a single visibility window.
  • Elevation limits remove the noisy low-altitude segments where atmospheric extinction and obstructions dominate.
  • Twilight scaling approximates visual detectability—higher Sun altitudes heavily compress the usable viewing time.
  • For binocular or radio work you can relax the daylight factor, but the geometric portion of the window remains the same.

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