Data & calculations

We use your selected location only to calculate which publicly tracked orbital objects are above your local horizon. You can use your browser location, search any place, or type coordinates. Your location is stored on your device and never required — you can clear it above at any time.

Orbital element data comes from CelesTrak, a long-standing public source. These “GP” element sets describe the estimated orbits of publicly cataloged Earth-orbiting objects. Object identity and classification come from the CelesTrak SATCAT.

CelesTrak refreshes orbital data about every 2 hours and its catalog metadata once or twice a day. We fetch on that schedule through a server-side cache and never from your browser, to respect their usage policy.

A curated few thousand objects: crewed and space-station objects, bright naked-eye satellites, weather, science, navigation, and geostationary satellites, recent launches, and the major tracked debris groups — rocket bodies, inactive payloads, fragments, and unknown objects.

Not all debris is tracked. More than 25,000 objects larger than 10 cm are cataloged, but an estimated half a million objects between 1–10 cm and over 100 million larger than 1 mm are not individually tracked. We say “tracked debris” and “publicly cataloged objects,” never “all debris.” Some restricted or classified objects may also be missing or have limited metadata.

We combine orbital elements, your location, and the current time to estimate each object’s position using SGP4 propagation — the standard model for these element sets. This runs in your browser, in a background thread. An object is “above” you when its computed elevation is greater than 0° over your local horizon.

An object can be above your horizon without being visible. To be seen with the naked eye it must be sunlit while your sky is dark, and bright enough. Most tracked debris is small and never naked-eye visible. We label visibility conservatively — when in doubt, we say it is not visible.

Predictions are estimates. Accuracy depends on how fresh the orbital elements are, and degrades if an object maneuvers, is dragged by the atmosphere, or has recently launched or fragmented. We show each object’s element epoch and a confidence label, and we deprioritize objects with stale data.

Debris does not get a “worth looking up” score, because most of it is not visible. Instead we score historical and orbital significance: membership in a known breakup or collision event, size, altitude and expected lifetime, and age in orbit. This is about context and history, never danger.

Orbital data: CelesTrak. Location search: Photon and Nominatim, © OpenStreetMap contributors. Propagation: satellite.js (SGP4). Map outlines: Natural Earth. Debris population figures: NASA Orbital Debris Program Office and ESA.