There aren’t any road signs to tell us the distances to remote galaxies. So astronomers look for the next-best thing: stars that flicker. The way they flicker helps reveal how far away they are. Astronomers use those distances to help learn such details as the age and fate of the universe.
Lots of stars flicker.
Cepheid variables, for example, pulse in and out like beating hearts. They get brighter and fainter with each beat. And there’s a relationship between the length of the beats and a star’s true brightness. So by measuring the beats and how bright the star looks, astronomers can determine how bright it really is.
It’s like seeing a faint light down a dark highway. If you know it’s a porchlight, then it must be fairly close. But if you know it’s a searchlight, then it must be far away. So knowing how bright a star is tells astronomers its distance as well.
Another type of star flickers just once: a Type 1a supernova. That’s because it marks the star’s total destruction. The way it brightens and fades reveals its peak brightness — and, therefore, its distance: possibly billions of light-years.
Finding the distances to these stars reveals the scale of the universe. Astronomers combine that with measurements of how fast the stars’ home galaxies are moving away from us to determine how the universe is expanding. That helps tell us how old the universe is — and what will happen to it in the distant future.