Thursday, June 18, 2009

The Sleeping Dragon

Well placed in the northern sky during spring, the constellation of Draco the Dragon winds sinuously between the Big and Little Dippers in the constellations of, respectively, Ursa Major and Ursa Minor. Although the Dippers are among the most-viewed asterisms (recognizable star patterns) in the night sky, Draco often goes unnoticed.

Dare we wake the sleeping dragon?

Draco in J. Middleton’s 1842 star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

1) About an hour after your local sunset time, face north. 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 left shoulder to the west, and you’ll be facing approximately north.

Looking north to the Dippers and Draco
Star maps created with
Your Sky

2) Locate the Big Dipper in Ursa Major and the Little Dipper in Ursa Minor. Midway between the bowl of the Little Dipper and the very bright star to the east, Vega in the constellation Lyra, is a quadrilateral of fainter stars. This is the asterism known as the Lozenge, and it marks the head of Draco (DRAY-koh).

3) The brightest of the four corner stars of the Lozenge is the orange giant Eltanin. Eltanin (ELL-tuh-ninn) is from the Arabic for serpent. Moving counterclockwise around the Lozenge from Eltanin, we next come to the yellow supergiant star Rastaban. Rastaban (RAH-stuh-bahn) is from the Arabic for serpent’s head.

The Lozenge asterism in Draco

The third corner star in our roundabout has no traditional name, so we call it Nu (NOO) for its star catalog designation. Nu is a binary system, two stars— in this particular case, both white stars— in orbit around each other. With the naked eye we see their combined light as one star. If you have binoculars, use them to look at Nu. You should be able to spot the nearly identical pair.

The orange giant Grumium completes our dragon’s head. Grumium (GROOM-ee-yum) is from the Latin for snout.

The Lozenge asterism was so-named not because it resembles a cough drop, but rather because a lozenge is a diamond-shaped figure. Granted, the misshapen boundaries of this dragon’s head can only be described as a diamond in the rough.

Astronomy Essential: A star's visible color depends on its surface temperature.

Although star color is sometimes subtle, we can observe it, especially when we’re comparing two stars of different colors. Stars that look red, orange, or coppery are at the cool end of the stellar temperature range. White, yellow-white, and yellow stars are in the middle of the range. Our Sun is a yellow star.

The stars at the hot end of the temperature range appear blue and blue-white, the former being the hottest. The average temperature of a blue star ranges between 56,000 and 87,000 degrees Fahrenheit. Now that’s hot.