Unit 4
Stars and Their Properties

The stars have fascinated humankind since ancient times. The names ancients gave patterns among stars are still used, and some of the common names of individual stars, such as Sirius, have been handed down to us from the Greeks. Others, such as Aldebaran, survive in sometimes distorted forms from the Arabic. More recently, especially interesting stars have been named after an astronomer who studied them; Barnard’s star, for example.

The ancients could note only the position and apparent brightness of a star. In the nineteenth century, however, astronomers began to develop techniques for measuring distances to stars. Once we know the distance to an object, we can determine the amount of energy it radiates. The nineteenth century also saw the development of spectroscopy, which allows astronomers to determine the physical properties and composition of a star. From these beginnings came the science of astrophysics, which was developed to explain how stars generate the enormous energy they give off, and how they evolve. Today, we have a very good understanding of stars, their structures, and their evolution. This unit will introduce you to these topics.