These are the largest of all. A beautiful example is Betelgeuse in the constellation of Orion. It is about 1,000 million km across. Rigel is one of the brightest stars to the naked eye. Although it is only one tenth of the size of Betelgeuse, is still 100 x larger than our sun.
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 either when they are very young , or when they are very old or dying . Currently there are more than 28,000 known variable stars. Star Nurseries . A good example of a star nursery is once again in the constellation of Orion.