When there isn’t enough oxygen in your blood, the skin or membrane below the skin turns a purplish-blue color. Learn more about possible causes.

A Blue Moon is a rare occurrence that depends on the timings of full moons during the year. We will experience a Blue Moon this year, here's what to expect.

Rigel is a blue supergiant that is the brightest star in the constellation Orion (the Hunter). Due to its measured size and brightness it is expected to end in a supernova one day. It also has two ...

Blue purple aurora photographed in Norway. (Image credit: marouan touil via Getty Images) Blue and purple auroras are even less common and also tend to appear during periods of high solar activity.

Get the facts on cyanosis, or bluish discoloration of the skin. It's a serious sign your body isn't getting enough oxygen. Learn about treatment and more.