Thursday, August 13, 2009

The Snake Handler

We continue our exploration of the prominent summer constellation Ophiuchus the Snake Handler (oh-fee-YOO-kuss) with a closer look at the stars that make up its central asterism, the Coffin.

Asterisms are recognizable star patterns that help us navigate around the sky and figure out which constellation we’re in. The Big Dipper is an example of a more well-known asterism; it’s a star pattern within the constellation of Ursa Major the Big Bear.

Although the largest summer constellation, Ophiuchus is virtually unknown except among seasoned sky observers. Perhaps its difficult spelling and pronunciation have something to do with that. Perhaps it pales in comparison to neighboring constellations Scorpius the Scorpion and Sagittarius the Archer, which are each favored with brighter stars and more distinctive star patterns that really jump out at the observer. And perhaps it’s a conspiracy perpetrated by astrologers.

OK, just kidding on that last one. But it is interesting to note that Ophiuchus is, in effect, the thirteenth sign of the zodiac. The zodiac is the daisy chain of constellations that encompasses the paths the Sun, Moon, and planets take across the sky, as seen from Earth. In addition to the 12 conventionally-known zodiacal constellations, the Sun, Moon, and planets travel through Ophiuchus. And there have certainly been babies born while the Sun was in Ophiuchus. Yes, there are some Snake Handlers out there masquerading as Archers and Scorpions.

The band of the zodiac
Diagram by
Dr. Guy Worthey

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.

Looking south to Scorpius and Ophiuchus
Star maps created with
Your Sky

2) Locate the distinctive curve of the scorpion’s body, just above the southern horizon. Ophiuchus essentially rides on the back of the scorpion. So look north of the scorpion for the large Coffin asterism, which comprises the brightest stars in Ophiuchus. It’s known as the Coffin because it resembles an old-fashioned casket with a pointed head.

The stars of the Coffin asterism

3) The brightest star in Ophiuchus marks the pointed top of the Coffin. Its name, Rasalhague, comes from the Arabic for head of the serpent collector. Rasalhague (RAH-sahl-hayg) is a white giant star, as much as four times more massive than our Sun.

4) Moving counterclockwise around the Coffin from Rasalhague, we next come to Cebalrai, an orange giant star. Cebalrai (SEH-buhl-rye) is from the Arabic for the shepherd’s dog, a reference to an ancient Arabic tradition that saw that part of the sky as a pasture.

5) Next we come to Sabik, at the base of the Coffin. Sabik (SAH-bick) is the second brightest star in Ophiuchus, and its name is from the Arabic for the leading one. Sabik is a binary, that is, two stars in orbit around each other. In this case, both stars are white and of nearly the same brightness. Although we are seeing the combined light of two stars when we look at Sabik, it appears to the naked eye as one star.

6) The star in the middle of the Coffin’s base has no traditional name, so we call it Zeta after its star catalog designation. Zeta is a blue-white dwarf star. The next Coffin star, marking the western corner of the base, is Yed Prior. Yed Prior, a combination of Arabic and Latin, means the foremost hand. This star marks the left hand of the snake handler, the one that grasps the snake’s head. Yed Prior is a red giant star.

7) Finally, we complete the Coffin back up at the pointed end with Kappa, another star with no traditional name and known only by its star catalog designation. Kappa is a white star.

For a look at a few of the Snake Handler’s deep-sky delights for binocular and telescope viewing, visit my previous post and the one before that.

Ophiuchus in John Flamsteed’s 1729 star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

Those of you in the health care field may be interested to know that in Greek mythology, Ophiuchus was identified with Aesculapius (ess-kyoo-LAY-pee-yus), the god of medicine. Perhaps there is an ancient connection between Ophiuchus/Aesculapius and his sinuous snake, and the caduceus (kuh-DOO-shuss)— the staff with two entwined snakes that has come to symbolize a physician.

A caduceus
Drawing by Rama and Eliot Lash

Astronomy Essential: One fifth of the world’s population can’t see the Milky Way.

Light pollution— excessive and inappropriate use of artificial night lighting— has impacted humankind’s view of the night sky. One-fifth of the world’s population can no longer see the glowing band of the Milky Way, because the sky is washed out by artificial light, much of it directed upwards. This phenomenon is at its worst in the United States, where two out of three residents cannot be inspired and awed by a view of their home galaxy.

Using properly shielded light fixtures that direct light only onto the ground, where it is needed for safety and security, is one effective solution to the problem.