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.