During just the last few years of the twentieth century, astronomers began to find planets orbiting other stars. They also made detailed measurements of the remnant radiation left over from the Big Bang and identified the first appearance of structure in the universe, the structure that eventually led to the formation of stars and galaxies. Some astronomers even found tantalizing evidence that suggests that the expansion of the universe may be speeding up, perhaps because of previously unrecognized properties of space itself. These important findings and many others lead to a particularly exciting time to consider a career in astronomy or space science.

When considering such a career it is important to realize that nowadays most astronomy is not classical astronomy—observing or photographing astronomical objects. Instead it involves the use of physics, mathematics, or geology to understand these objects. Many "astronomy" departments at...