SAIPH (Kappa Orionis). Orion's magnificence stems from the striking figure that appears like the outline of a person looking back at you. But he -- she to the Arabs -- would be little without the brilliance of his stars. Topping the list in beauty are Rigel and Betelgeuse and the three stars of the belt. They so dazzle that we pay less heed to Orion's other bright stars, Bellatrix (which ranks number 3) and Saiph (number 6, and brighter than Mintaka at the right-hand end of the Belt). As bright as it is, mid-second magnitude (2.06), Saiph scored only Bayer's Kappa designation. Even its name is borrowed. "Saiph" comes from a longer Arabic phrase that means the "sword of the giant," and originally referred to Orion's famed Sword that drops below his belt and contains the great Orion Nebula. The name was then erroneously transferred to the lower left star of Orion's seven-star figure, and it stuck. One of the hotter stars in the constellation, Saiph, with a temperature of 26,000 Kelvin, is a hot class B (B1) bright supergiant that shines with a sparkling blue-white light. At a distance of 720 light years, it pours its radiation into space at a rate 65,000 times greater than does the Sun (after a small correction for interstellar dust absorption). Though at about the same distance as Rigel, Saiph looks fainter because its much higher temperature causes the star to radiate much of its light in the invisible ultraviolet. From its spectrum -- its array of colors -- Saiph is classed as a "bright supergiant," implying that it is well along in its evolution, having entirely stopped hydrogen fusion. Confusingly, however, its luminosity and temperature place it close to the region of hydrogen-fusion stability, as if it were just in the process of developing into a supergiant. Whether true supergiant or not, it is still large, both the luminosity combined with temperature and a direct measure of angular diameter agreeing on a star about 11 times the size of the Sun. Saiph seems to be single, and though it has a few peculiarities (notably a slightly variable spectrum), it makes a good background source of light with which we can study the matter in interstellar space. Though its chemical composition seems otherwise normal, Saiph has only about a tenth the solar carbon abundance. The star's great luminosity tells of a large mass perhaps around 15-17 times that of the Sun. At such a mass, the star will (after expanding into a red supergiant) fuse its interior elements into iron, which will then collapse. And Saiph will explode. Thanks to Monica Shaw, who helped research this star.
- - Written by Jim Kaler