Here's why:
* Age: Main sequence stars are in the longest and most stable phase of their lives, fusing hydrogen into helium in their core. This is where they spend the majority of their existence.
* Size: Main sequence stars come in a range of sizes, but they are generally considered to be "average" in terms of stellar size. Our Sun is a main sequence star, and it's a good example of a typical star.
* Temperature: The temperature of a main sequence star is directly related to its size and mass. Larger, more massive stars are hotter and brighter than smaller, less massive stars.
The Hertzsprung-Russell (H-R) diagram is a useful tool for classifying stars. Main sequence stars form a diagonal band across the diagram, indicating their relationship between temperature, luminosity, and size.
