Here's why:
* Giant stars are much larger and more luminous than main-sequence stars. They have exhausted the hydrogen fuel in their core and have begun to fuse heavier elements.
* Main-sequence stars, like our Sun, are in the stable phase of their life cycle, fusing hydrogen into helium in their core.
* Yellow dwarfs are a type of main-sequence star with a surface temperature of about 5,200 to 6,000 degrees Celsius, like our Sun.
The Sun is expected to become a red giant in about 5 billion years, when it runs out of hydrogen fuel in its core. But for now, it's comfortably a main-sequence star, powering our solar system.
