Jimmy Westlake: Diamond in the spring skies
April 12, 2011
Steamboat Springs — Each season of the year brings its own unique geometrical pattern of bright stars into our early evening sky. Summer has its summer triangle, fall has the great square of Pegasus, winter has the magnificent winter hexagon, and spring offers us the spring diamond.
The spring diamond asterism, also known as Virgin's Diamond, is marked at its corners by four of the brightest stars adorning the spring sky. Their names are Arcturus, Spica, Cor Caroli and Denebola. Arcturus and Spica are easy to spot not only because of their flashy brilliance, but also because the curving handle of the Big Dipper points them out for us so conveniently. Simply follow the arc of the handle to Arcturus and then spike on to Spica.
Arcturus forms the diamond's eastern tip. This bright orange star already is in the advanced stages of life and has swelled up into an orange giant, 34 times larger than our sun. At a distance of only 37 light years, Arcturus is the brightest star visible in the sky's northern hemisphere and the second-brightest star visible from Northwest Colorado.
Spica marks the diamond's southern tip. Its icy blue color stands in sharp contrast to orange Arcturus. Spica is a blue supergiant star that shines 260 light years away and is the 10th-brightest star in our sky. The name Spica means "the ear of wheat" and comes from the same root word as spaghetti.
The other two stars in the diamond are trickier to locate because they aren't quite as bright as Arcturus and Spica. The northern tip of the diamond is marked by the star Cor Caroli, or Charles' Heart, named in honor of King Charles II of England. Locate Cor Caroli by again using the curved handle of the Big Dipper: If you imagine the Dipper's handle to be an arc of a complete circle, Cor Caroli would be near the center of this circle. Cor Caroli is one of the most beautiful double stars in the sky and is well worth closer scrutiny through a telescope.
Denebola marks the diamond's western tip. The name Denebola literally means "the tail of the lion." It represents the tuft of hair on the end of the tail of Leo the Lion. Denebola is 36 light years from Earth, one light year closer to us than Arcturus.
Near the center of the diamond is the star Vindemiatrix, the "grape gatherer." Both Vindemiatrix and Spica belong to the constellation Virgo.
This year, the bright planet Saturn is passing through this region of the sky and adds an extra "star" to the Spica-Denebola side of the diamond. Don't resist the urge to point your telescope at Saturn and view its spectacular rings and moons.
Each of the four corner stars of the diamond falls in a different constellation, so, once located, the spring diamond can help you find many other gems of our springtime sky.
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 across the world. His column appears weekly in the Steamboat Today. His "Cosmic Moment" radio spots can be heard on local radio station KFMU. Also, visit Westlake's website at http://www.jwestlake.com.