It's a wonderful way to end a wonderful day.
As evening approaches on Christmas, Dec. 25th, step outside and look west toward the setting sun. Even before the sky turns completely dark you can see them: brilliant Venus and the crescent moon hanging together not far above the horizon--a beautiful sight.
Right: The Venus-moon conjunction of Dec. 25th will look much like this one, photographed by NASA scientist Vince Huegele from the banks of the Tennessee river in Alabama on Nov. 25, 2003. [ Larger Image]
Venus is so bright it's often mistaken for an airplane or a UFO. Onlookers have been known to call 911 when they see it. And when lots of people notice Venus, police phones can ring off the hook. Dec. 25th could be such a night because together the moon and Venus are unusually eye-catching.
Here's something to think about while you're gazing at Venus: Its pearly-white light looks icy and cold, but with a surface temperature of 860 F (460 C) Venus is the hottest world in the solar system. A block of lead placed on the ground there would quickly melt. Venus is so hot because it has a dense atmosphere (90 times more so than Earth's) made of 96% carbon dioxide--a planet-warming greenhouse gas. Also, Venus is thoroughly blanketed by clouds, leaden-grey and laced with sulfuric acid. These oppressive clouds, ironically, are what make the planet seem from a distance so bright and lovely. They're excellent reflectors of sunlight.
Above: Stars and planets in the western sunset sky on Dec. 25, 2003.
The crescent moon beside Venus on Dec. 25th will be equally lovely--a slender arc of bright light cradling the dark lunar disk. Look closely. Can you see a ghostly glow across the whole moon? Leonardo DaVinci first understood this phenomenon some 500 years ago. It is sunlight reflected from Earth onto the moon. Astronomers call it "Earthshine."
Side-by-side with Venus, a crescent moon with Earthshine is regarded as one of the prettiest sights in the heavens. And the ensemble is bright enough to see even from light-polluted cities.
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Space Station Christmas -- (Science@NASA) Santa and his reindeer bring some holiday cheer to the International Space Station. 'Twas the Night Before Christmas, NASA-Style -- (Thursday's Classroom) A far-out rendition of a Christmas classic, with classroom or home-school lesson plans. Interplanetary Christmas -- (Science@NASA) In an exclusive interview with Science@NASA, Santa discusses his plans to deliver presents to future space colonies. Don't Gawk and Drive -- (Science@NASA) It's one of the loveliest sights in the heavens: Earthlight reflected from the Moon. Leonardo DaVinci's Codex Leicester -- Leonardo's observations of the moon in its crescent stage led him to one of the most important scientific statements in this Codex -- that sunlight reflected from the Earth's oceans acts as a secondary light of the moon. |