def JD2epochBessel(JD):
    """
----------------------------------------------------------------------
Purpose:   Convert a Julian date to a Besselian epoch
Input:     Julian date (e.g. 2445700.5)
Returns:   Besselian epoch (e.g. 1983.9)
Reference: Standards Of Fundamental Astronomy, 
           http://www.iau-sofa.rl.ac.uk/2003_0429/sofa/epb.html
Notes:     e.g. 2445700.5 -> 1983.99956681
           1 Tropical Year is 365.242198781 days
           JD(1900) = 2415020.31352
           If we know the JD then the Besselian epoch can be 
           calculated with:
           BE = B[1900 + (JD - 2415020.31352)/365.242198781]
           Expression corresponds to IAU SOFA expression with:
           2451545-36524.68648 = 2415020.31352
---------------------------------------------------------------------- 
   """
    return 1900.0 + (JD - 2415020.31352) / 365.242198781
