How big is Betelgeuse really?

EARLIER THIS YEAR, FURORE surrounded Betelgeuse — the star had ‘fainted,’ dimming more than expected in its usual cycle of brightness changes, leading some to suggest the star might go supernova sometime soon. But even as astronomers begin to get a handle on the red giant’s unexpected behaviour, they’re still struggling to understand its basic properties — namely its size and distance.

Meridith Joyce (Australian National University) and colleagues reported that Betelgeuse