Thanks to James B. Kaler. These contents are the property of the author and are reproduced from original without the author's express consent because of fair use and valid educational purposes.


Kochab, an obscure Arabic name that might simply mean "star," is just barely the second brightest, and appropriately the Beta, star in Ursa Minor, and represents the top front bowl star of the Little Dipper. Only 15 degrees from the north celestial pole, middle northerners can see it every night as it plies its small circular path. Together with the other bowl star (Pherkad, the Gamma star), it makes a small asterism called the "Guardians of the Pole," the two seeming in myth to "protect" the pole star. Though we are quite familiar with the major two motions of the Earth, daily rotation and annual revolution, the third motion, precession, is more obscure. The Moon and Sun act on the Earth's rotational bulge, and cause the axis to wobble over a 26,000 year period. The result is that the axis continually moves in a small circle against the background stars. Polaris is thus only a temporary pole star that will get better into the next century and then will begin to shift away. About the year 1100 BC, the pole made a reasonably close pass to Kochab, and there are old references to THIS star being called "Polaris." Precession also causes the vernal equinox (where we find the Sun on the first day of spring) to move backwards through the constellations of the zodiac; the equinox is now in Pisces rather than in Aries where it was when the constellations were being named. Unlike the Sun, Kochab (which is not particularly unusual among its class), has run out of internal hydrogen fuel, and is an evolving orange giant star that is now running for awhile on the fusion of helium deep in its core. At a distance of 126 light years, we calculate that it is almost 500 times more luminous (and about 50 times bigger) than our Sun. It appears about the same brightness as much more luminous Polaris because it is much closer and because, at a temperature of 4000 degrees Kelvin, it radiates a fair amount of its light in the infrared where we cannot see it. It has a reputation as a marginal "barium star," the element only a small bit enhanced relative to what is found in the Sun.