Converts a Julian Day object into a specific format.  For
    example, Modified Julian Day.
    Parameters
    ----------
    jd: float
    fmt: str

    Returns
    -------
    jd: float

def __to_format(jd: float, fmt: str) -> float:
    """
    Converts a Julian Day object into a specific format.  For
    example, Modified Julian Day.
    Parameters
    ----------
    jd: float
    fmt: str

    Returns
    -------
    jd: float
    """
    if fmt.lower() == 'jd':
        return jd
    elif fmt.lower() == 'mjd':
        return jd - 2400000.5
    elif fmt.lower() == 'rjd':
        return jd - 2400000
    else:
        raise ValueError('Invalid Format')