Amalie Stokholm

A star trembles like a bell after being struck. These tremors, tiny fluctuations in brightness and surface, can be caught by a telescope. From the frequencies of these 'stellar notes,' astronomers infer what's happening inside: how old the star is, how it's structured.

31 Aquilae is an aging star that has puffed up into a subgiant. It once resembled the Sun, but has since cooled and grown larger. It rotates very slowly — one full turn takes many days.