Here's a breakdown of why:

* Size: Red giants are significantly larger than our Sun, often having radii 10-100 times greater.

* Temperature: They are relatively cool compared to other stars, with surface temperatures ranging from about 3,500 to 5,000 Kelvin. This cooler temperature gives them their reddish hue.

Important Note: The term "red giant" refers to a specific evolutionary stage of stars, rather than a distinct spectral class. Stars become red giants after exhausting the hydrogen fuel in their core and transitioning to fusing helium into carbon.

Let me know if you have any other questions about stars!