There are about six thousand stars visible by naked eye from Earth. Some of these are small and close, while others are larger and farther away. Of all the stars that we can see with our eyes, there is one star that stands out - Mu Cephei.
This star of fourth magnitude can be seen in the direction of the constellation Cepheus under a dark sky. Its diameter is about 1,500 solar diameters. This makes it the largest star visible to the naked eye and one of the largest in the entire galaxy. If it were placed in the solar system, Mu Cephei would encircle Jupiter and almost touch Saturn's orbit!
Mu Cephei is a very cold red supergiant, with a surface temperature of 3700 Kelvin. Taking into account its brightness in the visible and infrared light
, it appears to be as much as 350,000 times brighter than the Sun! The only reason it does not appear brighter in the sky is due to its distance of 3000 light years.
The star has a current mass of about 20 solar masses. As with all very massive stars, Mu Cephei has a much shorter lifetime than the Sun. It is believed that the star has currently finished burning hydrogen in its core and has switched to burning helium into carbon. In a few million years, when the cycle of nuclear reactions ends, the star will no longer be able to counteract its gravity and will explode, becoming a supernova.
Credit: David Cruz.
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