A star is a large, hot ball of gases. It gives off its own light. Scientists view stars from different points in Earth’s orbit. When observed from two positions, the star appears to shift its location in a process called parallax. Scientists measure this shift to determine how far the star is. A light-year is used by astronomers to specify distances in space. One light-year is approximately 9 trillion kilometers. Light leaving Alpha Centauri will reach Earth in 4.3 years. You can locate a star by looking for its constellation, or a number of stars that form a pattern. You would look for the constellation named Orion to find the star Rigel.