Skip to main content

epj

sofars::cal

Function epj 

Source 
pub fn epj(dj1: f64, dj2: f64) -> f64
Expand description

Julian Date to Julian Epoch.

This function is part of the International Astronomical Union’s SOFA (Standards of Fundamental Astronomy) software collection.

Status: support function.

§Given:

  • dj1, dj2: Julian Date (Note 4)

§Returned:

  • Julian Epoch

§Notes:

  1. Julian Epoch is a method of expressing a moment in time as a year plus fraction.

  2. Julian Epoch J2000.0 is 2000 Jan 1.5, and the length of the year is 365.25 days.

  3. For historical reasons, the time scale formally associated with Julian Epoch is TDB (or TT, near enough). However, Julian Epoch can be used more generally as a calendrical convention to represent other time scales such as TAI and TCB. This is analogous to Julian Date, which was originally defined specifically as a way of representing Universal Times but is now routinely used for any of the regular time scales.

  4. The Julian Date is supplied in two pieces, in the usual SOFA manner, which is designed to preserve time resolution. The Julian Date is available as a single number by adding dj1 and dj2. The maximum resolution is achieved if dj1 is 2451545.0 (J2000.0).

§Reference:

Lieske, J.H., 1979, Astron.Astrophys. 73, 282.