[Robotbeat]

The radius is often not known. Radius is found most easily with transiting exoplanets, which are easy to detect but also only visible if you're lined up along the plane of the exoplanet's orbit.

You can also possibly find it via imaging, but even then, since you can't directly resolve it better than a point light source, you're making assumptions about albedo that lead to a wide dispersion in possible radii. High resolution optical imaging would require a telescope roughly 1-2km in diameter. Pretty tough... and because of the glare of the star, would be nearly impossible to image with an interferometric (i.e. non-filled-aperture) telescope since the light gather power would be so low. However, astronomers are incredibly clever at pulling data out of tiny points of light, so there may be some way.

[bmgxyz]

Thanks for this, it's quite interesting.

I have a friend who used to work in a lab doing super-resolution microscopy (i.e. beating the diffraction limit by various means) for use with bio/medical applications. Some of the techniques he told me about have to do with more or less taking lots of data from many images and assembling it all into something meaningful. I suppose what you're describing as "pulling data out of tiny points of light" is kind of the same thing. It's just that the scale is different.