Geometry modes

The Geometry tab sets the line of sight from the observer to the object. Choose one of four modes.

Mode	You give	LightCurve computes
Phase	Signed phase angle, phase-plane tilt, range	Line of sight, elevation, azimuth
Az / el	Azimuth, elevation, range	Phase angle
Orbit (TLE or OEM)	An element set or an ephemeris	Position at every instant, range, phase, passes
Measured	An observation file (CSV or CCSDS TDM)	The measured line of sight at every instant

Phase mode

The line of sight turns by the signed phase angle away from the anti-Sun direction, in a plane tilted by τ from the celestial east–west direction. Range presets: LEO, MEO, GEO, Moon.

Az / el mode

The satellite is fixed in the sky of the station. Use it for a geostationary object, or to explore one direction over a night: the 24-hour curve keeps the same azimuth and elevation.

Orbit mode (TLE or OEM)

Load an orbit

Pick one of the sample objects (ISS, Starlink, Astra 1KR, Hubble, the Chinese station, NOAA 15, SL-16 and Falcon 9 rocket bodies), paste a two- or three-line element set, load a .tle file, or download it from CelesTrak by NORAD number (Internet needed).

Optionally, use an ephemeris

Load an OEM replaces the TLE with a CCSDS Orbit Ephemeris Message, interpolated between its states. See CCSDS formats.

Go to a pass

The list of observable passes (48 hours) gives start, end, maximum elevation and duration. Click one to go to its highest point.

In orbit mode the range, azimuth, elevation and phase become results; the 24-hour curve follows the real trajectory; the nadir attitude aligns with the orbital plane.

SGP4 positions are accurate to about 1 km at the TLE epoch, then degrade by a few km per day in low orbit. A warning appears when the simulated date is more than 7 days from the epoch.

Measured mode

The scene follows the line of sight of a real observation, interpolated between measurements. Outside the measured period the nearest line of sight is held. See Measurements.