Sunday, April 17, 2011

Saturn Forms Triangle with Moon and Star Saturday

Skywatchers who are outside Saturday evening have a chance to see an eye-catching celestial array as the nearly full moon, a bright planet, and a bright star gather together in the night sky. The cosmic configuration should be visible at about 8:30 p.m. local time, weather permitting, and will resemble a rather large isosceles triangle in the east-southeast sky about one-quarter of the way up from the horizon.

Accompanying the moon will be the planet Saturn, shining sedately with a yellowish-white glow to the moon's upper left, with the bright, bluish star Spica hovering to the lower left of the moon in the zodiacal constellation of Virgo. The moon will likely appear "full" to most observers, but April's full moon won't officially occur until Sunday night.

Saturn triangle returns

The moon, of course appears to pass Spica every month. But in recent months, Saturn has been nearby too, and so for the last several months we've referred to this trio as the "Saturn Triangle." This sky map of Saturn, the moon and Spica shows how the triangle will appear.

What makes this triangle isosceles (a triangle with at least two equal sides) is that Spica will be located at an equal distance from both the moon and Saturn: 13 degrees. So the Spica-moon and Spica-Saturn sides of the triangle will measure a bit more than a fist's width in length. The side of the triangle from the moon to Saturn will appear just 8 degrees long.

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