Physics
Ephemerides and orbits
Sun, Moon, Earth rotation, station position and orbit propagation.
| Quantity | Model | Accuracy |
|---|---|---|
| Sun position | Astronomical Almanac low-precision formulae | about 0.01° |
| Moon position | Astronomical Almanac low-precision series | about 0.3° |
| Earth rotation | Greenwich mean sidereal time, IAU 1982 | — |
| Station | WGS84 ellipsoid | — |
| Precession (J2000 → date) | IAU 1976 angles ζ, z, θ | — |
| TLE orbits | SGP4 (satellite.js) | about 1 km at epoch, a few km per day in LEO |
| OEM orbits | Cubic Hermite interpolation of positions and velocities | metres at 60 s steps in LEO |
Nutation, polar motion and UT1 − UTC are neglected: they move the geometry by arcseconds, which does not matter for photometry.
The orbit mode uses the TEME frame of SGP4 as the inertial frame of the simulator; the difference with the frame of the Sun and the Moon is of the order of an arcsecond.
Moon phase
Section titled “Moon phase”The illuminated fraction of the Moon and its phase angle drive the scattered moonlight of the sky background.