Jimmy Westlake: The planetary superhighway

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Jimmy Westlake

Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.

Find more columns by Westlake here.

Our solar system is flat, like a pancake. That is to say, the planets orbit the sun in nearly the same plane, like marbles rolling around on the floor. And, all of the planets move in the same direction around the sun - counterclockwise as viewed from above the Earth's North Pole. The moon, too, orbits the Earth in nearly the same plane that the planets orbit the sun and in the same direction.

When viewed from Earth's surface, the moon and planets seem to follow the same narrow path through our sky, centered on a line called the ecliptic and passing through the 12 constellations of the zodiac. The moon moves the fastest, completing a trip around the zodiac in just more than 27 days and, of the planets visible to the unaided eye, Saturn moves the slowest, taking nearly 30 years to circle the zodiac.

It should come as no surprise that as the moon and planets travel around this planetary superhighway at different rates, they occasionally pass one another in the night. During the remainder of this month, the moon will pass three bright planets and provide three spectacular views for Earthly sky watchers.

On the evening of May 19, the slender crescent moon will appear less than 1 degree away from the dazzling planet Venus in a remarkably close conjunction. You'll be able to spot the pair even before darkness falls, and in fact, they will appear most striking in the multicolored sunset glow. Use a pair of binoculars to enhance the view. You'll also be able to see a beautiful phenomenon called earthshine, in which sunlight reflecting off the Earth illuminates the darkened nighttime portion of the moon. Don't miss this stunning spectacle.

On May 22, you can spot the moon positioned between the ringed planet Saturn, on the moon's right, and Leo's bright star Regulus, on the moon's left.

Finally, on May 31 you can watch the full moon and the brilliant planet Jupiter rising together in the southeastern sky at about 9:30 p.m. The pair will be visible all night long, setting in the west just as the sunrise brightens the eastern sky. This full moon will be a rare "blue moon" because it will be the second full moon to fall in the month of May.

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 Web sites 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. He also records a radio spot called the "Cosmic Moment" for local radio station "The Range" at 107.3 FM.

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