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Wyoming Skies for April

March 30, 2009

A monthly look at the night skies of Wyoming, written by Ron Canterna, professor in the University of Wyoming Department of Physics and Astronomy.

Our conspicuous winter constellations of Orion and Canis Major are slowly disappearing at dusk on the western horizon, in preparation for our long-awaited summer.

The April night is dominated by the familiar constellations, Ursa Major or the Big Bear, Leo the Lion, and the Gemini twins. Ursa Major and Leo are visible high toward the zenith and to the north. The Big Bear, also known as the Big Dipper, allows us to spot the pole star Polaris by following northward, a straight line from the two stars at the end of the dipper. Polaris is in the constellation Ursa Minor, called the Little Bear or the Little Dipper.

The Gemini twins, Castor (whitish) and Pollux (yellowish and brighter than Castor), are seen near the western zenith around dusk.

The Lyrid mteor shower will peak around April 21-22 with a nominal 20 streaks per hour. It is best seen after midnight in Lyrae, indicated by the bright star Vega. Saturn can be seen in Leo to the east of Regulus. A double treat for the morning of April 22 will be the occultation of Venus by the thin crescent moon.

April 2009 Interest: Searching for Planets, NASA's Kepler Mission

On March 6 of this year NASA successfully launched the Kepler satellite. Kepler is designed to survey more than 100,000 stars in the Cygnus region of the Milky Way galaxy and detect planets similar in size to the Earth.

This three-and-a-half-year mission should give astronomers sufficient data to search for planets located within the habitable zones of these stars. Using a 0.95 meter telescope and its complex system of 42 CCD detectors, Kepler will be able to detect and monitor periodic changes in a star's brightness pattern to within one part in 10,000. This minute change is due to the passage of these small planets across the star's luminous disk. Stars can exhibit such small changes in brightness from naturally occurring processes in their atmospheres such as sunspot activity and flares.

The key to discovering a planet is that these variable brightness patterns will recur in a periodic fashion. This time period will not only indicate the presence of an orbiting planet, it can also provide the planet's mass and size. NASA's Kepler mission is a great adventure in our search for extraterrestrial life in the universe.

For more information, visit the Wyoming Skies home page ( or send an e-mail to

Posted on Monday, March 30, 2009

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