What Is #22: A Variable Star?

The 'What Is' Series

A couple of months ago I started a new series on this blog titled "What Is". Thus far the focus is on the field of astronomy where we hear all sorts of cool science taking place in space. The goal of this series is to explain the details of different objects we hear about relatively frequently.

Variable Stars

When we take a look at the Sun we see a star that is very stable, but even stable stars such as the Sun vary. The Sun has a cycle of 11 years in which its activity increases and decreases. However, this doesn't classify the Sun as a classic variable star. When astronomers refer to variable stars, they refer to stars with a measurable brightness change over a period of time. If the Sun were many light years away, we likely would not see it varying over time. The variations are too small to detect from a large distance with current technology.

Common variable star types are Cepheid variables, RR Lyrae variables, and Delta Scuti variables. There are other types as well, but these are the main types. The different categories describe variations in brightness of different levels and lengths. Variable stars are interesting as they provide information on the inner workings of a star. Something must cause the variation and therefore the level and length of the variation provide clues on how stars evolve.

One of the more well known variable stars, although you likely don't know it as a variable star, is Polaris, the North Star. Polaris has a variation period of about 4 days and its magnitude change is about 0.3, a brightness change of about 130%. Without detailed astronomical equipment, however, you are unlikely to notice this change, although you could if you took detailed naked eye observations night after night under dark sky conditions. But that's not something most of us are doing. :-)

Stars are interesting objects and when they vary in brightness they are even more interesting. They bring up new questions and provide new information to our understanding of the cosmos.