Trail Forecaster

Observing site

Latitude °

Longitude °

Altitude m

Exposure window · UTC, 24h

Start

End

Darkness threshold

Target

or enter coordinates manually

RA J2000 °

Dec J2000 °

Optics & camera

Saved rigs

Focal length mm

Pixel size µm

Sensor width mm

Sensor height mm

Rotation ° E of N

Sub length s

Elements refresh server-side every 2 h (CelesTrak GP/SupGP). Magnitudes are diffuse-sphere estimates (±1 mag); flares aren't modelled. A search margin absorbs GP cross-track error.

How it works

Set your site, exposure window, target, and optics, then run. Current orbital elements are propagated with SGP4 in a background worker — every satellite, entirely in your browser — to find which ones cross your sensor's field of view, timed to a fraction of a second, with the path across the frame and an estimate of how badly each trail marks a sub.

Crossings while a satellite sits in Earth's shadow leave no trail — they're shown dimmed. The night timeline stacks sunlit crossings over shadowed ones per half-hour, so the busy hours after dusk and before dawn stand out from the quiet middle of the night, and marks your cleanest stretch.

sunlit · leaves a trail twilight in shadow cleanest stretch