Variable stars have a brightness that changes from Earth’s perspective. They are of interest to astronomers and can be intrinsic or extrinsic. Amateur astronomers can contribute to research by collecting data.
A variable star is a star with a brightness that varies from the perspective of an observer on Earth. Some variable stars have variations so subtle they can only be identified with advanced spectroscopy, while others vary enough to be seen with the naked eye or with a basic telescope. Variable stars are of immense interest to astronomers, both professional and amateur, and more are continually being identified.
Historically, people thought of the stars as fixed and unchanging. This theory was debunked when people started observing novae, realizing that the contents of the skies actually changed over time. A number of theories have been developed to explain it, and astronomers have begun to identify variable stars. Initially, very few were developed and were thought to be relatively rare. With the advent of better observing equipment, astronomers realized that variable stars were actually quite numerous. Some examples of well known variable stars include Betelgeuse, Beta Lyrae, Eta Aquila and Polaris.
There are several types of variable stars. They are roughly divided into two main categories: intrinsic and extrinsic variables. Intrinsic variable stars have a brightness that varies due to internal processes taking place in the star. Stars actually vary quite a bit at the beginning and end of their lives due to a series of cascading processes that occur in and around the star. Extrinsic variables vary due to factors external to the star.
In the case of an extrinsic variable star, the star’s brightness can vary due to periodic occultation by another star, which means that another star crosses its path and temporarily eclipses it. Stars can also vary in brightness as they rotate if they have dark areas on their surfaces. Both of these types of variable stars have a very regular period, making it easy to follow the increase and decrease in brightness.
Intrinsic variables are divided into cataclysmic, pulsating, eruptive and X-ray variables. These stars are undergoing processes such as chemical changes that cause variations in brightness as the star swells and contracts, emits energy flares, and so on. Novae are a particularly notable example of a cataclysmic variable star, with a glow of brightness so intense that, in the case of the largest novae, the star can light up the sky.
Amateur astronomers interested in variable stars can actually contribute to the body of scientific research on variable stars. Amateur observing organizations collect data from astronomers around the world and provide that data to astronomers. Occasionally, an amateur astronomer will even identify a variable star or notice changes in a variable star before professional astronomers notice; thanks to the sheer number of celestial bodies, it’s impossible for professional astronomers to keep track of everything at all times.
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