Kepler ellipse timing and anomaly conventions
Research context
research method · conditional · As of 2026-10-10
An elliptic two-body ephemeris solves Kepler's equation for eccentric anomaly at a declared time origin, then transforms orbital-plane coordinates to the observing frame.
Key knowledge
An elliptic two-body ephemeris solves Kepler's equation for eccentric anomaly at a declared time origin, then transforms orbital-plane coordinates to the observing frame. Use consistent radians; JPL's degree formula rescales eccentricity by 180/pi.
Values and equations
M=n(t-t_peri)=E-e sin E; n=sqrt[G(M1+M2)/a^3]; r=a(1-e cos E); ν=atan2(sqrt(1-e^2) sin E, cos E-e)
- M,E,ν
- Mean, eccentric and true anomalies rad
- e
- Eccentricity 1
- n
- Mean motion rad s^-1
- a,r
- Semimajor axis and separation m
- t,t_peri
- Consistent dynamical time and pericentre epoch s
- G
- Gravitational constant m^3 kg^-1 s^-2
- M1,M2
- Masses kg
Conditions and scope
- Bound elliptic two-body motion, 0≤e<1; perturbations, light-time and relativistic timing are additional models.
- Quoted JPL approximate element tables have finite validity intervals and are not a precision navigation ephemeris.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Approximate positions of the planets: Orbital-plane coordinates, time range and iterative Kepler equation (selected source body inspected).
2026-10-10 · Bounded source check of the recorded statement and conditions. This does not certify a unique physical model, reproduce the cited study or replace independent branch review.
Entry details
Permanent link to this entry ↗- Record identity
- research-earth-kepler-timing
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference