Today, scientists know that the Universe is constantly changing. In the 1860s, astronomers discovered that each star has a different pattern of dark lines in its rainbow spectrum. These lines allowed scientists to compare stars. Among other things, the patterns of the lines enable astronomers to find out which elements make up each star. Another important tool for analyzing stars is color.
Blue stars are considerably hotter than red stars.
Astronomers have found that the size of a star has a significant impact on how long it lives and how it affects nearby planets. An average star like our Sun steadily burns its hydrogen fuel, creating a comfortable range of temperatures on Earth for billions of years. Smaller stars burn their fuel slowly, but tend to send out huge flares of harmful radiation. These smaller stars cannot support life on the planets that may orbit them. At the other extreme, big stars explode after a few million years, broiling any nearby planets.