To categorize stars, astronomers make a graph of each newly formed star’s brightness versus its temperature. Each star’s measurements create a dot on the diagram. If we join up all the dots, a curved line is created that astronomers call the Main Sequence. Every star’s brightness and temperature on the Main Sequence remains relatively unchanged for millions to billions of years. But stars, like people, come in different sizes. Main sequence stars that are more massive than our Sun are very bright and hot. These massive stars use up their nuclear fuel within less than a few million years. Stars less massive than our Sun are fainter and cooler and can last for tens of billions of years on the Main Sequence.
