def parallax(d):
    """
    Returns parallax in arcsec given distances.
    Args:
        d (float): distance
    Return:
        parallax in arcsecs
    Written by: Logan Pearce, 2017
    """
    from astropy import units as u
    d = d.to(u.pc)
    x = 1 * u.au / d
    return x.to(u.arcsec, equivalencies=u.dimensionless_angles())
