def epj2d(epj):
    """
    Converts Julian epoch to Modified Julian Date.

    Inputs:
    - epj   Julian epoch

    Returns:
    - mjd   Modified Julian Date (JD - 2400000.5).

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

    History:
    P.T.Wallace Starlink    February 1984
    2002-07-11 ROwen  Converted EPJ2D to Python and renamed.
    """
    return 51544.5 + (epj-2000.0)*365.25