Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.
Find more columns by Westlake here.
Most of the stars in our sky shine with a steady, unchanging light, save for the rapid twinkling that occurs because of turbulence in the Earth's atmosphere. It's rather surprising to learn that some stars can vary their light output by a factor of hundreds or even thousands in only a few days, weeks or months. These variable stars offer us the opportunity to witness rapid evolutionary changes in the lives of the stars.
One of the most remarkable of the variable stars is Omicron Ceti, also known as Mira. Mira has been noticed off and on by astronomers throughout the centuries, all the way back to the Greek astronomer Hipparchus in 134 B.C. But it was an amateur astronomer, David Fabricius, who, in 1596, realized that this star was a variable star. The great astronomer Johann Hevelius coined the name Mira for this star in 1662, a name that means "Wonderful."
Modern astronomers recognize Mira as the prototype of a class of variable stars called red giant variables. At its faintest, Mira fades to magnitude 10, far below naked-eye visibility, and, at its brightest, it can shine as brightly as a second magnitude star, similar to the three stars that form Orion's Belt or the stars in the Big Dipper. When at maximum brightness, Mira is nearly 1,600 times brighter than when it is at minimum brightness. Imagine what it would be like if our sun was a variable star that sometimes shined 1,600 times brighter than at other times. Beating like a giant heart, Mira slowly pulsates during a period of 332 days. When at its brightest, as it is now, Mira also is at its largest diameter - more than 700 times larger than our sun! Red giant stars like Mira are near the ends of their lives and grow unstable. Eventually, Mira will blow away its bloated, outer atmosphere, exposing its burned-out core, destined to become an ultra-dense white dwarf star.
Astronomers think the sun will one day become a bloated red giant like Mira, swallowing the Earth and the other inner planets as it balloons outward. Catch Mira, the "Wonderful Star," now, before it starts to fade back into obscurity for another year. Look for a reddish-colored medium-bright star about 7 p.m. midway between the brilliant "evening star" Venus in the west and the familiar constellation of Orion, the Hunter, in the east.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. His "Celestial News" column appears weekly in the Steamboat Pilot & Today. His "Cosmic Moment" radio spots can be heard on local radio station KFMU. Also, check out Jimmy's Web site at www.jwestlake.com.