What are stars? They are heavenly bodies that we see with the unaided eye in the night sky. Stars are extremely hot white balls of gas, which are very compact and have great relative velocities (the rate with which they rotate in a given direction). A star is a highly evolved thermonuclear object made up of a hydrogen nucleus surrounded by a complex nuclear fuel. The most common stars are the Sun, Jupiter, Saturn, Uranus, Neptune, Triton, Rhea, and Hale-Bopp.
Stars are thought to be moving through space at a fraction of the speed of the Earth, which makes stars unlike anything else in the universe. The total mass of such a star would be many times more massive than the planet Earth. Stars can only be found with telescopes; infrared and optical images are not sufficient for astronomers to detect individual stars, although they can detect the presence of other solar systems and other large celestial bodies orbiting around other stars.
Why do astronomers study stars? They study them because they are stars themselves, and that makes them unique. Astronomers want to learn more about the processes that go on in planetary systems similar to our own, and how these stars got their start. Studying stars also helps us to understand the makeup of the universe and to test theories of gravity and cosmology. Although there is evidence of several theories in cosmology (including the fine-tuning of the planets and the big bang theory), astronomers must also study the properties of stars to confirm or refute such theories. Astronomy is an exciting and important area of science and exploration.