By Jimmy Westlake, professor of physical science, Alpine Campus
After Monday’s full Paschal Moon, the stage is set for Easter Sunday on April 4. According to ancient tradition, Easter Sunday is the first Sunday after the Paschal Moon, so the date of Easter can come as early as March 22 or as late as April 25.
This year, there is a special celestial treat that culminates on Easter Sunday. The two inner planets, Mercury and Venus, will shine together side-by-side in our evening sky right after sunset.
A meeting of two or more planets in the sky is called a conjunction and, although Mercury and Venus will be seen close to each other for the next two weeks, they will appear closest together on Easter Sunday, so that is the official date of their conjunction. After the sun goes down that evening, Venus and Mercury will be seen through the colorful glow of the sunset, about a hand-span at arm’s length above the western horizon at 8:00 pm. Both planets will be easily visible to the unaided eye as the sky darkens. Venus, the brighter of the two, is actually the more distant on that evening, gleaming at us from 146-million miles away. Mercury, the fainter, will appear only 3º to Venus’ right, shining from 91-million miles away. Just four days later, on April 8, Mercury will reach its greatest angle east of the Sun. These circumstances combine to make this the best evening appearance of Mercury in 2010.
Mercury, the closest planet to the Sun, completes an orbit in only 88 days. It is also the smallest of the planets, since Pluto was booted from the planet club in 2006. Mercury’s daytime high temperature climbs to 800º F, but at night, it plummets to -280º F. This gives Mercury the most extreme temperature variations of any planet in our solar system. In March 2011, NASA’s MESSENGER spacecraft will drop into orbit around Mercury and will no doubt revolutionize our thinking about the smallest planet.
Venus has been described as the Earth’s “twin” or “sister” planet, because the two worlds are nearly the same size, mass, and density. But the similarities end there. Venus’s surface environment is like a hellish pressure cooker, with a crushing atmospheric pressure 90-times that of Earth and a temperature of 900º F, day and night. Without oceans of liquid water to dissolve carbon dioxide out of its atmosphere, the way Earth’s oceans do, Venus’ runaway greenhouse effect has turned her into Earth’s very “twisted sister.”
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 newspaper. His “Cosmic Moment” radio spots can be heard on local radio station KFMU. Also, check out Jimmy’s website at www.jwestlake.com.