I stepped outside the other night to watch the stars come out after a beautiful sunset. It was the first clear, moonless night in what seemed like a month. Facing west, I saw the dazzling planet Venus in the colorful sunset glow. Then, glancing around the sky, I noticed another bright star that seemed out of place. I took a moment to get my bearings and realized that I was looking toward the constellation of Cetus, the Whale. Aha! That explained it! The famous variable star named Mira was at maximum brightness. For a moment, I felt the way that the stargazers of old must have felt when they saw an unfamiliar star in this part of the sky.
Mira has been noticed off and on by astronomers over the centuries, all the way back to the Greek astronomer Hipparchus in 134 BC. 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 long period red giant variable star. At its faintest, Mira fades to magnitude 10, far below naked-eye visibility, and at its brightest, it shines as a second magnitude star, similar to the three stars that form Orion's Belt. At maximum light, Mira is nearly 1600 times brighter than at minimum light! Beating like a giant heart, Mira slowly pulsates over a period of 332 days. When at its brightest, as it is now, Mira is also at its largest - - over 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 a white dwarf star.
Astronomers think that 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 bright star about two outstretched hand lengths to the upper left of Venus around 7 PM.
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 on the websites of CNN.com, NASA's "Astronomy Picture of the Day," Spaceweather.com, Space.com, Discover.com, and in Sky & Telescope, Astronomy, Night Sky, Discover, and WeatherWise magazines. His "Celestial News" article appears weekly in the local Steamboat Pilot newspaper. He also records a radio spot called the "Cosmic Moment" for the local radio station "The Range" at 107.3 FM.