def mjd2sdssjd(mjd):
    """
    Converts a Modified Julian Date to a SDSS Julian Date, which is
        used at Apache Point Observatory (APO).

    Parameters
    ----------
    mjd : float (any numeric type)
        A Modified Julian Date

    Returns
    -------
    mjd : float
        The SDSS Julian Date calculated from the input Modified Julian Date

    Notes
    -----
    - The SDSS Julian Date is a convenience used at APO to prevent MJD from rolling
        over during a night's observation.

    Examples
    --------
    >>> mjd2sdssjd(55580.90429)
    55581.20429

    """
    return mjd + 0.3