Transcript: The size of a star is a fundamental quantity, but it’s very hard to measure because stars are so far away. The Sun, our nearest star, is half a degree across on the plane of the sky, but if we move the Sun to a distance of one parsec its size would be about a hundredth of a second of arc. Atmospheric blurring of stellar images blurs them to 50 to 100 times larger than this, so when we see stars on an astronomical image it never reflects the true size of a star, just the blurring of the Earth’s atmosphere. At a distance of 10 parsecs where there’s significant numbers of stars, the size of a star would be a thousandth of an arcsecond, and to detect surface features we’d need even higher resolution. So only the very largest and nearest giant or super giant stars have ever been resolved by astronomical observation.