Frequently asked questions
How live satellite tracking works, where the data comes from, and how accurate it is.
Is the satellite tracking real-time?
Yes. Every satellite is propagated live in your browser from its most recent orbital elements, so the position you see is computed for the current moment (or the moment you fast-forward to). Nothing is pre-recorded — the globe advances in real time until you pause or warp the clock.
How accurate are the positions?
Positions come from the same SGP4/SDP4 model and public TLE data that professional trackers use, so they are typically accurate to within a few kilometres for recently updated low-Earth-orbit objects. Accuracy degrades as an element set ages and for satellites that manoeuvre; WatchSat shows the age of the data so you can judge it. It is intended for visualization and education, not for collision avoidance or targeting an antenna.
What is a TLE?
A Two-Line Element set (TLE) is a compact, standardized description of a satellite’s orbit at a specific moment (the "epoch"): its inclination, eccentricity, mean motion, and other Keplerian-style parameters packed into two 69-character lines. TLEs are published by the US Space Force and distributed through CelesTrak, which is where WatchSat gets them.
What is SGP4?
SGP4 (Simplified General Perturbations 4) is the standard mathematical model that turns a TLE into a position and velocity at any given time. It accounts for the most important orbital perturbations — Earth’s oblateness and atmospheric drag among them. WatchSat runs SGP4 (via the open-source satellite.js library) for thousands of objects continuously.
How often does the orbital data update?
WatchSat refreshes its catalog from CelesTrak through an edge-cached proxy roughly every 30 minutes, and CelesTrak itself typically publishes new element sets for active objects one to several times per day. The tracker also ships with a recent snapshot so it loads instantly and works even if the live feed is briefly unavailable.
Can I see the ISS or other satellites from where I live?
Yes — select a satellite (for example the ISS) and use “When can I see it?” in its panel. Share your location (or type coordinates) and WatchSat computes the next naked-eye passes from where you stand: rise time, direction, maximum elevation, and duration. Passes cluster around dawn and dusk, when your sky is dark but the satellite is still catching sunlight.
Where does the data come from?
Orbital data comes from CelesTrak (which redistributes US Space Force tracking data); Earth and celestial imagery comes from NASA, ESA, and USGS. All are credited on the attribution page. TLE data is public.
Read how WatchSat is built, open the live globe, or contact us.