The Surface Of Mira Mira, a popular variable star, is one of only three stars to have images taken showing the shape and actual surface of the star. The other two are the Sun and Betelgeuse. More info on Mira can be found in our Variable Star of the Month archives. Variable stars are stars that change in brightness. These brightness changes can range from a few hundredths to as much as twenty magnitudes over periods of a fraction of a second to years, depending on the type of variable star.
Stars change in brightness when they are very young, or when they are very old or dying.
There are now over 30,000 stars known to be variable, and 14,000 more that are suspected to be changing in brightness in our galaxy, the Milky Way. Research on variable stars is important because it can provide much information about stellar properties, such as mass, radius, luminosity, temperature, internal and external structure, composition, and age. This information can then be used to understand other stars. Professional astronomers have neither the available time nor the unlimited telescope access needed to gather data on the brightess changes of thousands of variable stars.