Given a proleptic Gregorian calendar date, return a Julian date float.

def julian_date(year, month=1, day=1, hour=0, minute=0, second=0.0):
    """Given a proleptic Gregorian calendar date, return a Julian date float."""
    return julian_day(year, month, day) - 0.5 + (
        second + minute * 60.0 + hour * 3600.0) / DAY_S