def JD2epochJulian(JD):
    """
----------------------------------------------------------------------
Purpose:   Convert a Julian date to a Julian epoch
Input:     Julian date
Returns:   Julian epoch
Reference: Standards Of Fundamental Astronomy,
           http://www.iau-sofa.rl.ac.uk/2003_0429/sofa/epj.html
Notes:     e.g. 2445700.5 converts into 1983.99863107
           Assuming years of exactly 365.25 days, we can 
           calculate a Julian epoch from a Julian date.
           Expression corresponds to IAU SOFA routine 'epj'
----------------------------------------------------------------------
   """
    return 2000.0 + (JD - 2451545.0) / 365.25
