def get_box(wcs, radec, w):
    """Get box of width w around source coordinates radec.

    Parameters
    ----------
    radec : tuple
        RA and DEC in degrees.
    w : int
        Width of box.
    wcs : astLib.astWCS.WCS instance
        World Coordinate System.

    Returns
    -------
    box : tuple
        A box centered at radec.

    """
    raPix, decPix = wcs.wcs2pix(*radec)
    raPix = int(raPix)
    decPix = int(decPix)
    box = slice(decPix - int(w / 2), decPix + int(w / 2)), slice(raPix -
        int(w / 2), raPix + int(w / 2))
    return box
