Here's why:

* Large: Red giants are significantly larger than our Sun.

* Cool: They have a lower surface temperature than our Sun, hence their reddish color.

* Upper Right: On the H-R diagram, stars are plotted based on their temperature (x-axis) and luminosity (y-axis). Red giants are cool (low temperature) and very luminous (high luminosity), placing them in the upper right corner.

Additional Information:

* Red giants are in a later stage of stellar evolution than our Sun. They have exhausted the hydrogen fuel in their core and have expanded significantly.

* Examples of red giants include Betelgeuse (in Orion) and Aldebaran (in Taurus).