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Can we reveal the actual optical disk of another star than our sun's?
The answers are yes – yes, we have telescopes that large; yes, we've seen the disks of other stars, and yes, we're even directly imaging planets now.
First, as you've remarked, we have several large segmented-mirror telescopes that are on the order of 10 meters (~33 feet) in diameter. Interestingly, these were not the first telescopes to actually image a star. In '95-6, astronomers from Harvard used the Hubble Space Telescope (a diameter of only ~2.4 meters, ~8 feet) imaged Betelgeuse, a red supergiant in the constellation of Orion. (See the press release at http://www.cfa.harvard.edu/press/archive/betel97.html).
Image Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA
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