As the Sun drops below the horizon this evening, a beautiful drama begins to play out in the western sky: the Moon and the planet Venus fading into view through the twilight.
Venus is the brilliant "evening star," not far to the lower right of the crescent Moon. They form the most striking duo in all the night sky.
Before night falls, though, another striking sight plays out like a slow-motion movie: the colorful display of twilight -- ever-changing bands of blue, yellow, orange, and red.
Twilight is the interplay between sunlight and Earth's thick, messy atmosphere.
As the Sun drops near the horizon, it shines through a thicker layer of air than when it's high overhead. Dust, volcanic ash, and other debris absorb the shorter blue wavelengths of light and allow the longer reds to shine through. So the more junk there is in the atmosphere, the redder the setting Sun appears. The same effect colors the setting Moon orange or gold.
The debris also reflects the redder wavelengths of sunlight, creating the bands of fiery color.
And finally, the atmosphere bends the fading sunlight -- curving some of the light back up over the horizon. The red wavelengths are bent at a more severe angle, so they're the last ones to fade from view.
Watch this colorful drama play out in early evening. Venus and the Moon are well above the horizon at sunset, and set in late evening.
Tomorrow: beaming into the universe.
Script by Damond Benningfield, Copyright 2010
For more skywatching tips, astronomy news, and much more, read StarDate magazine.