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.
(Beta Tauri). Equally well called El Nath, Elnath lies at the tip of the great northern horn of Taurus, the Bull. "El Nath" (actually al nath) from Arabic means the "butting one," the name transferred over from stars in Aries and obviously appropriate for Taurus as well (the ancient names in Aries no longer used). Bright second magnitude (1.65), Elnath is one of the sky's brighter stars, ranking 25th overall and number three within second magnitude, right behind Castor in Gemini and Bellatrix in Orion. Number two in Taurus (behind Aldebaran), it received the Beta designation from Bayer. Elnath is peculiar, however, as it is one of the sky's rare linking stars. Formally now in Taurus, the star is also a part of the classic outline of Auriga and is simultaneously Gamma Aurigae (though it ranks number two in Auriga as well, after Capella). (The other linking star, Alpheratz or Alpha Andromedae, is also Delta Pegasi.) "Gamma Aurigae" is never used, however. Elnath also has broader positional significance, as it is in the Milky Way only three degrees to the west of the anticenter of the Galaxy, the point directly opposite the Galactic Center in Sagittarius. In this broad direction lie vast dark cold clouds of interstellar gas and dust in which stars are being born. Physically, Elnath is a hot (13,600 Kelvin) class B giant star. From its distance of 130 light years, we find a luminosity (corrected for the ultraviolet radiation from the hot surface) almost 700 times that of the Sun. The radius derived from temperature and luminosity, 4.6 times that of the Sun, agrees well that found from the original measurement of angular diameter, though not with a more recent measure, which makes the star 35 percent larger, showing the difficulty of such observations. Like so many stars of its class, Elnath is "chemically peculiar" and appears to be a "mercury-manganese" star, the manganese abundance 25 times normal, the calcium and magnesium abundance reduced and only an eighth solar. These peculiarities are caused by the combined action of gravity and radiation, which make the atoms of some elements drift downward and out of sight and others rise. The best bright example, is, by rather amazing coincidence, the other "linking star," Alpheratz! Elnath has a mass of around 4.5 times that of the Sun. It is beginning to die, and if it has not already completely shut down the fusion of hydrogen in its core, it will before too long. Within only a couple million years, it will expand to become a cooler orange giant star.