If you have a small telescope handy, wander out and examine the star Algieba, the brightest star in the curved section of the “Sickle of Leo”. Also called γ Leonis, Algieba is a superb double star. Both components are evolved, swollen giants about twice the mass of our Sun which have run out of hydrogen and now burn helium in their cores.
Although Algieba lies in the part of Leo represented by the “mane” of the great lion, its name is Arabic for “forehead”. Without optical aid, this 2nd-magnitude star appears whitish-yellow. The two components are separated by a fairly tight 4″ (arc-seconds). That’s too close to split with binoculars, but most telescopes crack the pair without much effort. Even a 70 mm scope at 75x or more will split the pair cleanly in all but the most turbulent sky. The brighter star is a yellow-orange giant while the fainter 3rd-magnitude star burns with a pure yellow glow. Some observers report seeing pale red or even green in the fainter star. What can you see?
The Algieba system lies about 130 light years away. So in real terms, the stars are separated by 170 astronomical units (AU), about four times the distance of the Sun to Pluto. Astronomers have detected a large planet revolving quickly around the brighter star. Just a little more 1 AU away, the planet revolves around the star in about 420 days. The planet is at least nine times as massive as Jupiter.
The components of Algieba revolved about their center of mass every 500-600 years. So they’ve only made a half-turn since their discovery by the great William Herschel in 1782. Leo and Algieba are near the ecliptic so they’re visible from populated regions of the northern and southern hemispheres.
Just 2º northwest of Algieba lies the radiant of the Leonid meteor shower, an event which peaks around November 17 each year. The Leonids have been disappointing of late, but they have exhibited spectacular displays of meteors at roughly 33-year intervals. The Leonids in 1833 were a dazzling event, an unrelenting blizzard of hundreds of thousands of shooting stars over the course of an entire night. Observers watched the radiant of the shower move during the night, which strongly suggested that meteors were astronomical rather than atmospheric phenomena.