Methodology

How we calculate, why we chose, what we assume.

Every methodological choice is documented. From the Swiss Ephemeris configuration to the coordinate system convention to the time standard. If it affects the output, it's explained here.

Stack

Computational foundation

Ephemeris

Swiss Ephemeris (DE441 base, JPL)

Reference frame

ICRF · J2000.0 equinox

Coordinate system

Topocentric / geocentric, equatorial

Time standard

UT1, TT, TAI (fully disclosed per study)

Spatial precision

Geodetic coordinates, WGS84

Numerical precision

Arcsecond floor, double precision

Methodology Notes

Published documentation

Methodology Note

April 28, 2026

Time Standards in Modern Ephemerides: UT1, TT, TAI, and the Leap Second

Every astronomical calculation depends on a choice of time scale. We document which time standards we use, when they matter, and how to convert between them.