Frequently Asked Questions

Sky Lens cross-references every aircraft broadcasting ADS-B over Belgium, all satellite orbits, planetary and stellar positions, and active airspace at your exact location and time. Enter your observation details and it returns a probability-ranked list of candidates with evidence for and against each. Try it now →

Key discriminators: sound (drones buzz high-pitched and are audible only within ~200–400 m; planes roar audibly for 15–25 km), movement (drones can hover; aircraft follow straight tracks), and lights (aircraft have legally mandated red-left / green-right / white-strobe navigation lights; drones have no standard light pattern). Sky Lens checks ADS-B to confirm whether a registered aircraft was in the area at the time you report. Full guide →

Almost certainly SpaceX Starlink satellites. They're visible as a train of evenly-spaced white dots in the 30–60 minutes after sunset or before sunrise, moving in a perfectly straight line across the sky over 2–6 minutes. Individual dots don't flash or change colour — they glow steadily as they reflect sunlight. Sky Lens tracks 14,000+ orbiting objects including all Starlink constellations and can confirm the exact pass for your location and time. More about Starlink →

That's atmospheric scintillation — turbulence in the atmosphere refracts starlight through different air densities, causing rapid colour changes for stars low on the horizon. It's a pure optical effect, not a flashing light source. The bright star Sirius is notorious for this, especially in winter when it sits low in the south. Stars higher up and planets (which have a measurable disc rather than a point source) scintillate far less. Read the Field Guide →

Sky Lens uses a likelihood-ratio scoring pipeline. Every candidate — aircraft, satellite, planet, drone, static obstacle — receives a base prior probability. That probability is then multiplied by likelihood ratios derived from your observation inputs: direction, elevation, movement pattern, colour, sound, and duration. Hard geometric gates first remove physically impossible candidates: if the geometric elevation angle to an aircraft is below −0.3°, or if the terrain horizon blocks the line of sight, the candidate is excluded entirely before any scoring. Full methodology →

Currently Sky Lens covers Belgium with full real-time ADS-B data, combined with global satellite and celestial coverage. The satellite and celestial object identification (ISS, Starlink, planets, stars) works anywhere on Earth — just enter your coordinates. Benelux-wide ADS-B coverage is planned as a next expansion step.

Automatic Dependent Surveillance-Broadcast — a technology where aircraft periodically broadcast their GPS-derived position, altitude, speed, heading, and identity using an onboard transponder. Any receiver in range can pick up the signal without interrogation. Sky Lens ingests this data every 10 seconds via the airplanes.live network. Important caveat: military aircraft, some general aviation, and all drones under 25 kg are not required to carry ADS-B, so their absence from the data does not mean they weren't there. Learn more →

Military aircraft operate without civilian ADS-B — they use encrypted secondary radar systems (Mode S with military interrogators, MLAT, or dedicated military surveillance). Some vintage aircraft, ultralights, and paragliders also fly without transponders legally. Drones under 25 kg have no ADS-B requirement under EASA regulations. Sky Lens shows everything that broadcasts — and the absence of a match from ADS-B data is itself informative: it narrows down candidates towards non-broadcasting objects including drones and military aircraft. Read more →

Sky Lens uses primary-source data with quantified precision. ADS-B aircraft positions update every 10 seconds at typical 75–185 m horizontal accuracy from the aircraft's own GPS, interpolated between samples to about 50 m. Satellite positions are computed from CelesTrak TLEs refreshed daily, giving sub-degree angular accuracy within 24 hours of the TLE epoch. Terrain horizons use the 30 m SRTM digital elevation model from NASA. Real cloud positions come from EUMETSAT MTG-FCI satellite at ~2 km nadir resolution, refreshed every 10 minutes. Plate-solved photos achieve sub-degree pointing accuracy via star-pattern matching against the Tycho-2 catalog. Full precision breakdown →

Aircraft positions from airplanes.live (ADS-B Mode S) and the Open Glider Network (FLARM, OGN-tracker UAVs). Satellite ephemeris from CelesTrak TLEs via Skyfield's SGP4 propagator, covering 14,000+ catalogued objects including all Starlink constellations. Planets, Sun and Moon from JPL DE421 ephemeris. Terrain from NASA SRTM 30 m DEM via Open-Elevation. Buildings, masts and wind turbines from OpenStreetMap (Overpass API) plus the Belgian aviation obstacle inventory. Weather from aviationweather.gov METARs, Open-Meteo and Meteoblue. Real-time satellite cloud positions from EUMETSAT MTG-FCI. Airspace classes from AIP Belgium and skeyes. Plate-solving via Astrometry.net against the Tycho-2 catalog. Full source table →

Yes. Sky Lens polls airplanes.live (ADS-B Mode S) every 10 seconds and the Open Glider Network at sub-10-second cadence. Each aircraft sample carries the broadcaster's own GPS position at the broadcast moment, and positions are interpolated between samples down to about 50 m for searches in between. Satellite orbital elements are refreshed daily from CelesTrak. Real-time cloud cover from EUMETSAT MTG-FCI satellite updates every 10 minutes. Local weather grid updates hourly via Open-Meteo and Meteoblue.

FlightRadar24 is an aircraft tracker — it shows which aircraft are at which positions. Sky Lens is an observation-identification tool. Given a time, location, direction and brief description, it ranks every possible candidate (aircraft, satellite, planet, star, drone, balloon, static structure like a wind turbine) by likelihood. It cross-references ADS-B and OGN aircraft, satellite ephemeris, planetary positions, terrain line-of-sight from the SRTM digital elevation model, airspace context, and local weather all at once. Where FR24 answers "what aircraft is at this position", Sky Lens answers "what could that light I saw at 22:14 toward the southeast at 30° elevation possibly be". See the methodology →