Thursday, May 27, 2010

The Sickle

The zodiacal constellation of Leo the Lion, prominent in the spring night sky, isn’t hard to locate, primarily because of the large, distinctive star pattern at its leading edge. This recognizable pattern, or asterism, is called the Sickle. It resembles its namesake, the old-fashioned farm implement used to harvest grain crops.

The Sickle also resembles a backwards question mark. Within its generous sweeping curve, we can easily imagine what the ancients saw: a leonine head topped with a luxurious mane. The celestial lion faces west, the direction in which he appears to advance. This stealthy westward movement as the night wears on is due to Earth’s rotation toward the east.

In the Greco-Roman constellation tradition, Leo represented the Nemean Lion, one of the beasts slain by Hercules during his Labors. The star pattern was, in fact, seen as a lion by the ancient Persians, Turks, Syrians, Jews, Babylonians, and Egyptians.

Four of the six Sickle stars have traditional names. Let’s learn them.

1) About an hour after your local sunset time, face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

Star maps created with Your Sky

2) Look high in the sky, just west of the meridian. Leo strides across the heavens midway between the two bright stars Arcturus and Procyon. The Lion’s brightest star, Regulus (REGG-yoo-luss), marks the handle of the Sickle. Regulus is from the Latin for little king. Also known as the Lion’s Heart due to its placement in the imaginary lion’s body, Regulus is a blue-white dwarf star.

The stars of the Sickle

3) Moving up the Sickle from Regulus, the next star has no traditional name, so we call it Eta (AY-tuh) for its star catalog designation. Next in line is Algieba (al-JEE-buh), a naked-eye double star. The pair are giant stars, one orange and the other yellow. Can you see both component stars? You’ll need good eyes and a dark site. Or you can try splitting them with binoculars. Algieba is from the Arabic for forehead.

4) Continue on to Adhafera (ah-duh-FERR-uh), whose name is Arabic for lock of hair. Adhafera is a yellow-white giant, 200 times brighter than our Sun.

5) Next up is Rasalas (RAH-suh-luss), which is Arabic for lion’s head. Rasalas is an orange giant with an unusually high iron content. The terminal star of the Sickle has no traditional name, so we call it Epsilon for its star catalog designation.

In addition to being an easy-to-learn asterism well loved by beginning stargazers, the Sickle is the site of a reliable annual meteor shower. Every November, the famous Leonids appear to emanate from a spot in the Sickle. Although not currently producing meteor “storms” of hundreds of “shooting stars” per hour, as some of us (myself included) witnessed in 2001, the Leonids are still lovely. Come November, you’ll want to bundle up and find a dark site outside of town to view them. You can expect to see a dozen nice meteors per hour on or around the peak viewing night. Check this site for details.

When this king of the jungle roars, astronomers—both novice and veteran—sit up and take notice.