Alnilam, the middle star in Orion's Belt is brilliant blue in color. The brightness is due to a combination of high surface temperature and large surface area. Its surface temperature is about 25,000°C (45,000°F), which is four times hotter than the Sun. Alnilam will eventually turn into red supergiant. Astronomers say that it then explode as a supernova, and this is expected to take place within the next million years.
