Here's why:
* Main sequence stars are in the prime of their lives, fusing hydrogen into helium in their cores. They are relatively stable and will remain in this phase for a long time (billions of years for stars like our Sun).
* Red giants are stars that have exhausted the hydrogen fuel in their cores. They have expanded significantly and become cooler, giving them their reddish appearance. This is a later stage in a star's life.
Think of it like this:
* A main sequence star is like a young adult, full of energy and just starting their life.
* A red giant is like an elderly person who has lived a long life and is now entering their final stages.
Therefore, red giants are older than main sequence stars.
