Much can be learned of about the physical nature of comic objects by studying the wavelengths of the electromagnetic waves that they omit. Astrophysicst estimate the motion of a star or galaxy by measuring the shift in the wavelengths of its light. Enormous red shifts distant galaxies indicate that they are rapidly moving away from earth. This has led most astrophysicists to believe that the universe is expanding. The origin of this expansion was believed to be an explosion called the big bang, which resulted in the formation of the universe.
Cosmology is the study of the structure, dynamics, and development of the universe.
It tries to explain how the universe was formed, what happened to it in the past, and what might happen in the future. In 1610, however,following the use of Galileo's telescopic observations, our perception of the universe dramatically changed The earth is no longer considered the center and the universe is regarded as infinite. Since the distance involved is so great, a method of measuring the amount of time it takes for light to travel in a given distance is used to measure distances. When given certain distances between the sun and the earth, we can find the measurements between stars. The milky way is a large, disk-shaped aggregation of stars, or galaxy , that includes the sun and its solar system.