APOD: The Gaia Stars of M15 (2019 Mar 28)

[Ann]

What's the time-scale of this animation? Visible wavelengths?

APOD Robot wrote:

Plentiful in M15, RR Lyrae stars are evolved pulsating variable stars whose brightness and pulsation period, typically less than a day, are related.

So if we assume that the typical pulsation period of a RR Lyrae star is, say, 20 hours, I guess you can just stare at one pulsating star and see how many times it goes through a full pulsation cycle to figure out what length of time the animation covers.

As for the wavelengths of the pulsating stars, they belong to spectral classes A and F, so they are going to be a bit whiter than the Sun. I don't know if they change color as they pulsate, but they might change a little, if they are similar to the Cepheid stars in that regard.

As for the classical Cepheids, they get a bit bluer when they are brighter and redder when they are fainter, or at least that is how I read this figure.

Note that classical Cepheids are both brighter and redder than RR Lyrae stars. They also pulsate more slowly.

Ann