Astrophysics

Even looking close to the Earth, in our own solar system we see widely varying conditions. The properties of the rocky planet Mercury, very close to the Sun, differ dramatically from those of the gas giant Saturn, with its complex ring structure, and from the cold, icy Pluto. But the range of variations found in our solar system is minuscule when compared to that of the stars, galaxies, and more exotic objects such as quasars. The properties of all of these objects, however, can be measured by observation, and an understanding of how they work can be reached by the extension and application of the same physical laws with which we are familiar.

The first astrophysical concept or law to be recognized was the law of gravity. We are all familiar with the force of gravity. Although it is a very weak force compared to the other fundamental forces of nature, it is the dominant factor determining the structure and the fate of the universe. Large structures, such as galaxies, and smaller ones, such as stars and planets, coalesced due to the force of gravity, which acts over vast distances of space.

Much of the evolution of our universe is due to gravity's effects. However, scientists generally hold the view that the understanding of atomic processes marks the true beginning of astrophysics. Indeed, even such enormous objects as stars are governed by the interaction and behavior of atoms. Thus it is often said that astrophysics began in the early decades of the twentieth century, when quantum mechanics and atomic physics were born.