Many years ago, I remember learning at school that even with the most powerful telescopes (this was pre-Hubble), and pointing them at the closest stars, we still couldn’t resolve any more detail than just a point of light.
With today’s technology, are we able to see anything more than just a point of light? For example, a disc of a star? I’ve read a little about optical interferometry that can resolve down to crazy levels of detail - but how far are we from resolving an extrasolar star as more than a point? (I’ve seen pics where Hubble resolves a binary star system to two points of light.) If Hubble can’t do this - about about the NGST? I’ve also heard of “occlusion” techniques, whereby we are fortunate enough to be positioned such that an extrasolar planet occludes a star during transit - I believe I read that using this technique, we can (in a clumsy way) map a star’s brightness profile.
Bad Astronomer - if you’re listening, please enlighten me about this before Planet X sneaks up on us in a few week and causes widespread catastrophes on Earth
ISTR that on the highest resolution with Hubble, Betelgeuse is about five pixels across. All other stars except the Sun are less than one pixel. It is to be hoped that someone will correct this, and give facts for NGST and interferometry.
On the other hand, we’ve been able for a while to indirectly determine surface features of other stars. Stars can have “starspots”, slightly dimmer spots similar to sunspots, and as a star rotates and spots move into or out of view, the brightness will change slightly. Using computer models of the star, you can make a pretty good guess as to where the spots are on the star, how big they are, etc.
I don’t think that NGST will be able to do much better than Hubble on resolution. It will be larger, but on the other hand, it’ll probably be somewhat less precise in its shape, since it’ll be launched in pieces, and it’s going to be using infrared rather than visible light, which also decreases the resolution. The space-based interferometers should be able to resolve many stars faily easily, but that’s not the main reason you want a space interferometer. The primary mission of such a craft would be planet-finding. Also note that a simple (two telescope) interferometer only has good resolution in one dimension. You can get around this by rotating the array, but that wouldn’t let you see things like starspots very well, which can change significantly in the time it’d take to rotate. You can also add another telescope to the array, but that would cost more, and not add much capability for the primary mission, so don’t count on it.
