So I've read a number of times that you can't see an individual star in another galaxy. Yet Hubble and Leavitt used Cepheid variables to create a standard candle. How did they measure the period of a star in, say, M31?
It's absolutely possible to see individual stars in other galaxies. Hubble (the telescope) can measure cepheids as far as tens of millions years away. 100 years ago, the technology was just getting to a point where it was possible to study variable stars in the nearest galaxies.
We can see individual stars in other galaxies! Just not with the naked eye or an average backyard telescope.
Edit: here's a Hubble image showing individual stars in the Andromeda Galaxy: https://esahubble.org/images/heic1502a/
Thought you were going to show the other Hubble’s image of Andromeda: https://carnegiescience.edu/about/history/archives/plate-archives/m31var
Very cool - and that explains it. Fie on sloppy science writing . . .
It's absolutely possible to see individual stars in other galaxies. Hubble (the telescope) can measure cepheids as far as tens of millions years away. 100 years ago, the technology was just getting to a point where it was possible to study variable stars in the nearest galaxies.