Tonight the moon passes just a degree or so from Regulus the bright star of the constellation Leo.
Leo is one of the oldest and most distinctive constellations in the night sky. It lies due south around midnight in the spring. Tonight it is almost due west. The `head` of the lion is like a backward question mark drawn by the stars; alpha, eta, gamma, zeta, mu and epsilon Leonis.
The sky at 22:56 tonight
Nearby, in the constellation Cancer are the two planets Mars and Saturn.
The star alpha leonis, Regulus, is the most prominent star in shining at magnitude +1.36 which makes it the 21st brightest star. The name literally means `king` and comes from the latin `rex`. Regulus lies at a distance of 69 light-years and has an absolute magnitude of -0.7, and a surface temperature of 13,000K. The star has a +7.7 dwarf companion (also a double star), 177 arcseconds away. Regulus is one of the brightest stars that can be occulted by our solar system planets. Our Moon also occults the star over two `periods` of 18 months during it`s 18.6 metonic cycle. The last series of occultations happened in September 1999; we will have to wait until next year before it starts again.
Regulus and the Sun, (the tiny dot is the earth)
Like the Sun most stars rotate sedately about their spin axes. But Regulus spins much faster. The stars centrifugal force causes it to squash so that its equatorial diameter is one-third larger than its polar diameter. In fact, if Regulus were rotating about 10 % faster, its outward centrifugal force would exceed the inward pull of gravity and the star would fly apart. A curious phenomenon, known as "gravity darkening", where the poles becomes brighter than its equator, was detected by astronomers. The darkening occurs because the equatorial bulge diminishes the pull of gravity, which causes the temperature there to decrease.
