def to_df(self):
        """
        Returns DataFrame with photometry from observations organized.

        This DataFrame should be able to be read back in to
        reconstruct the observation.
        """
        df = pd.DataFrame()
        name = []
        band = []
        resolution = []
        mag = []
        e_mag = []
        separation = []
        pa = []
        relative = []
        for o in self._observations:
            for s in o.sources:
                name.append(o.name)
                band.append(o.band)
                resolution.append(o.resolution)
                mag.append(s.mag)
                e_mag.append(s.e_mag)
                separation.append(s.separation)
                pa.append(s.pa)
                relative.append(s.relative)

        return pd.DataFrame({'name':name,'band':band,'resolution':resolution,
                             'mag':mag,'e_mag':e_mag,'separation':separation,
                             'pa':pa,'relative':relative})
Returns DataFrame with photometry from observations organized.

        This DataFrame should be able to be read back in to
        reconstruct the observation.