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REGULUS

Regulus, glowing at the heart of Leo the Lion, one of the great constellations of the zodiac, is near the end of the list of first magnitude stars. At a distance of only 77 light years, it shines in our sky at magnitude 1.35, just marginally brighter than the next one down, Adhara, the second brightest star of Canis Major. The Latin name means "the little king," the reference to a kingly star going back to ancient times. Regulus marks the bottom of an asterism called the "sickle of Leo," a sickle-shaped figure that outlines the head of the celestial lion. The star is almost exactly on the ecliptic, the path of the Sun, and is regularly occulted, or covered over, by the Moon. Down and to the left of Regulus, find the brighter star Spica. The autumnal equinox, where the Sun crosses the ecliptic in September, lies right between the two. Regulus is a "main sequence" star, a so-called dwarf that like the Sun is fueled by the internal fusion of hydrogen into helium. Though technically a dwarf, Regulus is still visually 140 times brighter than the Sun, the luminosity climbing to 240 time brighter when the star's ultraviolet radiation is taken into account. Its luminosity and a temperature of 12,000 Kelvin show from theory that it has a mass some 3.5 times solar. Consistently, it is 3.5 times larger than the Sun, the figure derived both from temperature and luminosity and from a direct measure of angular diameter. Regulus has a distant lower mass companion located at least 4200 astronomical units away from it (100 times Pluto's distance from the Sun), which orbits Regulus with a period of at least 130,000 years. The companion is ITSELF a double separated by at least 95 astronomical units) in a thousand year orbit. Both stars are less massive and dimmer than the Sun. The brighter is an orange dwarf similar to the lesser component of Alpha Centauri, while the fainter is a red (class M) dwarf. From the little double, Regulus would look like a brilliant star six times brighter than our full Moon.