CHARA image of the rapidly rotating hot star Altair. Stellar rotation causes a star's shape to be flattened at the poles and bulged at the equator. Because the equator is further from the center of the star, it will appear cooler than the poles, an effect called "gravity darkening". The CHARA image reveals the strong effect of gravity darkening on the highly distorted stellar photosphere.
Click here to compare Regulus to other rapidly rotating stars.
Reference:
Imaging the Surface of Altair
Monnier et al. 2007, Science, 317, 324