Saiph, The Sword, also known as kappa Orionis, is a second-magnitude star that forms the right knee of the constellation of Orion, the Hunter. Consensus appears to be that Saiph is 720 light years from Earth, but figures up to 1500 light years can be found on the Web1. It, like many other stars in Orion, is a blue supergiant with a massive energy output, almost 60,000 times greater than that of our sun. Its surface temperature reaches 26,000 degrees Kelvin, which means that a large percentage of its light is radiated in the ultraviolet end of the spectrum - this is why it is comparatively less bright to our eyes than, for example, Rigel, which is a similar distance from Earth.

Saiph's diameter is 11 times that of our sun, but there is some disagreement as to whether it is a true supergiant star. Its spectrum indicates that it is in the 'dying' helium fusion phase of its life cycle, but its luminosity and temperature are so high that some astronomers think it is still fusing hydrogen, and only beginning the process of developing into a supergiant. Its mass (calculated from its luminosity) is more than 15 times that of the sun, which indicates that it will almost certainly end its life as a supernova, and perhaps even a black hole. After becoming a huge red supergiant star, its inner core will be fused into iron, which will then collapse under its own gravitational force.

Saiph's name comes from a longer Arabic phrase, Saif al Jabbar which means 'the giant's sword'. Confusingly, the star is not part of Orion's sword, and seems to have been mistakenly named. An alternative theory is that Saiph was named when a different configuration of Orion was recognized in the sky a long time ago.

1. Totally different figures for Saiph's diameter and distance from the Earth can be found here:
References and further reading:

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