Thursday, August 21, 2008

Arc to Arcturus

If you can locate the Big Dipper, you can easily locate the brightest star in our summer sky, Arcturus (ark-TOUR-uss). One of the first memory prompts that beginning stargazers learn is “arc to Arcturus.” Just extend the curve of the Big Dipper’s handle to the next star in that line that's brighter than the end star of the handle, and you’ll arc to Arcturus.

Chart created with Your Sky

Right now, Arcturus is also easy to spot if you simply face west one hour after sunset. Arcturus will be the brightest object in the western sky. At that time, planet Jupiter will be the only object in the sky that’s brighter; it’s the blazing star-like object in the southeast, over your left shoulder, so you shouldn’t confuse the two.

Arcturus is the fourth brightest star in the night sky, after Sirius (SEER-ee-uss), Canopus (kuh-NOPE-uss), and Alpha Centauri (senn-TARR-ee). Sirius is a winter star, and Canopus and Alpha Centauri are Southern Hemisphere stars. So, in the summer sky of the Northern Hemisphere, Arcturus rules.

Big and brilliant, Arcturus is 25 times the diameter of our Sun and 113 times as luminous. This orange giant star is the brightest luminary in the constellation of Bootes (Boh-OH-teez) the Herdsman. Arcturus is Greek for “guardian of the bear,” a reference to the star’s ancient association with its neighboring constellation Ursa Major (ER-suh). Ursa Major is the Great Bear, and the Big Dipper is the central star pattern or asterism of Ursa Major. Arcturus appears to trail the Great Bear, which moves counterclockwise around Polaris, the North Star. So you can see how fitting it is that we arc to Arcturus from the Big Dipper.

Arcturus lies 37 light years from Earth. A light year is the distance light travels in one Earth year, nearly six trillion miles. When you observe Arcturus, what hits your eyes is light that departed the star 37 years ago. You are receiving vintage starlight from 1971--starlight that began its journey the year that:

- China was admitted to the United Nations
- the voting age in the U.S. was lowered to 18
- Walt Disney World opened in Florida
- cigarette advertising ended on television
- Jim Morrison, lead singer of The Doors, was found dead in Paris
- Intel released the world’s first microprocessor
- Idi Amin took control of Uganda
- pocket calculators, floppy disks, and e-mail were invented
- the films Love Story and The French Connection were in the theaters
- Federal Express and Greenpeace were launched
- platform shoes and crushed velvet hot pants were all the rage

Stars are time capsules, and Arcturus is seriously retro.