From: Fundamental science

Cepheid variables are giant stars that pulse in brightness. Classical cepheids, such as the North Pole star, Polaris, brighten and dim on timescales of days. Their period is directly related to their brightness and so they provide good reference points for measuring distances in the nearby universe. They can be used out to distances of around 100 million light years beyond which they are hard to distinguish from surrounding stars. Astronomers have now shown that a rare and even brighter class of cepheid, called ultra long period cepheids, which pulse with periods of a few months or longer, can potentially be used as beacons to measure distances three times further. The change in their pulse rate as they age could also reveal much about how very massive stars evolve. [F][A][R]

Read more stories like this