Venus and the moon get together for yet another celestial dalliance on Thursday (Dec. 5), and you should be able to see the pair in a blue daytime sky.
This, however, will not be an exceptionally close approach between the two brightest luminaries of the night. Venus will appear well below and to the left of the crescent moon as darkness slowly falls, with the distance between the two objects measuring roughly 8 degrees. (Your clenched fist held at arm's length measures roughly 10 degrees.)
Of course, what we’re seeing is an illusion of perspective. Venus is 38.5 million miles (61.9 million kilometers) from Earth at the moment, while the moon is nearly 173 times closer at 222,800 miles (358,700 km) away. [ Best Night Sky Events of December 2013 (Sky Map Gallery) ]
Find it in the daytime!
Venus is now the most dazzling that it will be for all of 2013 and 2014 in either the evening or the morning sky. The planet is so bright that you can spot it in a clear blue sky before sunset, if your eye lands on the right point in the south-southwest.
With the moon relatively close by, here is a good chance for you to make a daytime sighting. At around 3:30 to 4 p.m. local time, look about one-third up in the south-southwest sky for the slender lunar crescent, just 11 percent illuminated by sunlight.
Once you find the moon, extend your fist out to the lower left of the moon and carefully scrutinize that part of the sky; Venus should appear as a tiny but distinct speck of light against the blue sky.
Higher now, lower later
As twilight comes on, Venus seems to grow increasingly large and bright.
Venus is highest in the sky during the first half of December; we're now seeing it as high as it will get this year, more than a full month after its greatest elongation from the sunon Nov. 1. The planet shines at essentially its maximum possible brightness all month, with the evening of greatest brilliance coming on Friday (Dec. 6)..
Nevertheless, this is not one of Venus' better apparitions. The planet is only about 20 degrees above the horizon 45 minutes after sunset during the first half of December. You may have to move around to get a view past local obstructions.
An increasingly slender sliver
This is also a fine time to examine Venus in a telescope. The planet wanes from a thick crescent to a much longer, very thin sliver during December while growing markedly in overall size as it gets closer to Earth. (The planet appears 27 percent illuminated on Thursday but is just 4 percent illuminated on New Year’s Day.)
How soon will you be able to discern Venus' crescent shape in binoculars ? A steady mounting for the binoculars can make all the difference, as can simply bracing them against the side of a tree.
Here is graphic evidence that the planet is swinging nearer to us in its orbit and showing us more of its night side: Venus' narrowing crescent grows 36 percent in apparent size this month. If you have exceptional (20/10) eyesight, you can challenge your vision with a critical test just after sunset in late December and early January. This period offers a particular fine opportunity to try to resolve Venus as a tiny crescent with your naked eyes.
Soon, a fond adieu
Look while you can. Earth's sister world is nearing the end of one of its low apparitions for observers at mid-northern latitudes.
Venus begins plunging back down toward the horizon in the second half of December. By Christmas Day (Dec. 25), it will be dropping rapidly into the sunset glow, and during the first half of January it will gain speed and vanish. For most of 2014, Venus will stay low in the dawn.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook and Google+. Original article on SPACE.com.
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