Plot the ra and dec of the coordinates,
        at a given epoch, scaled by their magnitude.

        (This does *not* create a new empty figure.)

        Parameters
        ----------
        sizescale : (optional) float
            The marker size for scatter for a star at the magnitudelimit.
        color : (optional) any valid color
            The color to plot (but there is a default for this catalog.)
        **kw : dict
            Additional keywords will be passed on to plt.scatter.

        Returns
        -------

        plotted : outputs from the plots

def plot(self, sizescale=10, color=None, alpha=0.5, label=None, edgecolor='none', **kw):
        '''
        Plot the ra and dec of the coordinates,
        at a given epoch, scaled by their magnitude.

        (This does *not* create a new empty figure.)

        Parameters
        ----------
        sizescale : (optional) float
            The marker size for scatter for a star at the magnitudelimit.
        color : (optional) any valid color
            The color to plot (but there is a default for this catalog.)
        **kw : dict
            Additional keywords will be passed on to plt.scatter.

        Returns
        -------

        plotted : outputs from the plots
        '''
        # calculate the sizes of the stars (logarithmic with brightness?)
        size = np.maximum(sizescale*(1 + self.magnitudelimit - self.magnitude), 1)

        # make a scatter plot of the RA + Dec
        scatter = plt.scatter(self.ra, self.dec,
                                    s=size,
                                    color=color or self.color,
                                    label=label or '{} ({:.1f})'.format(self.name, self.epoch),
                                    alpha=alpha,
                                    edgecolor=edgecolor,
                                    **kw)

        return scatter