Jimmy Westlake: Mercury, Venus return to the evening sky
October 31, 2011
Steamboat Springs — Mercury and Venus, the two innermost planets in our solar system, are moving out from behind the sun and into our early evening sky. For the first two weeks of November, these two "evening stars" will be within 2 degrees of each other. Then, the faster-moving Mercury will dive back between the Earth and sun and disappear from view by month's end.
Mercury is the smallest of the eight planets in our solar system once Pluto was demoted in 2006. It has been described as the "cannon ball" planet because 70 percent of its mass is made of pure iron. For comparison, Earth is composed of about 50 percent iron. Named for the swift-footed messenger god, Mercury completes an orbit of the sun in only 88 days. This rapid motion causes it to flip-flop between our evening and morning skies several times each year.
Venus has been described as the Earth's twin planet because the two worlds are nearly identical in size, mass and composition. Earth is only about 5 percent larger than Venus. But the similarities seem to stop there. The temperature on Venus hovers near 900 degrees Fahrenheit day and night under an oppressive atmosphere 90 times heavier than Earth's and made of almost pure carbon dioxide. For comparison, Earth's atmosphere contains only 0.03 percent carbon dioxide. The Venusian clouds rain sulfuric acid droplets, but most of this acid rain never reaches the ground. It evaporates as it falls into the scalding air near the surface. Like Mercury, Venus flip-flops between our evening and morning skies, but at a much slower pace. Consequently, Venus spends several months playing the role of our "evening star" and then several months as our "morning star."
To see Mercury and Venus this month, you will need an unobstructed view of the southwestern horizon. Venus will be the first to pop out in the colorful sunset glow, just a few degrees above the horizon around 6:30 p.m. Mercury will appear about 2 degrees below Venus as the sky darkens. Binoculars will enhance the view.
On Nov. 9 and 10, the bright star Antares joins the duo of planets, forming a striking "triple star." Then, on the night of Nov. 26, the slender crescent moon joins the planets for a spectacular sunset scene.
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. Visit his website at http://www.jwestlake.com.