THE DA VINCI GLOW
WATCH OUT FOR THE DA VINCI GLOW: If
you go outside tonight to witness the meeting of Venus and the crescent
Moon, pay special attention to the Moon. Cradled between the arms of
the slender crescent is a display of light and shadow that puzzled sky
watchers for thousands of years--until Leonardo Da Vinci figured it
out. It's the "Da Vinci glow," also known as Earthshine:
Richard Sears of Merced,
California, took the picture last night. "I was getting ready for the
Venus-Moon conjunction," he says. "The Earthshine was gorgeous."
For much of human history,
people marveled at the faint image of the full Moon inside the arms of
the crescent. Where did it come from? No one knew until the 16th
century when Leonardo figured it out. He realized
that dark lunar terrain was being illuminated by sunlight reflected
from Earth.
Visualizing this in the 1500s required a
wild kind of imagination. No one had ever been to the Moon and looked
"up" at Earth. Most people didn't even know that Earth orbited the
sun. Copernicus' sun-centered theory of the solar system wasn't
published until 1543, twenty-four years after Leonardo died. 
Above: Da Vinci's sketch of Earthshine in 1510 vs. Italian astronomer Riccardo Di Nasso's photo of Earthshine in 2006.
In Leonardo's Codex Leicester, circa 1510, there is a page entitled "Of the Moon: No Solid Body is Lighter than Air." He states his belief that the "ghostly glow" is due to sunlight bouncing off Earth's oceans and, in turn, hitting the Moon. 500 years later, we know that Earth's clouds (not oceans) do most of the reflecting; but that is a quibble. Leonardo understood the basics well enough.
Go outside tonight and look to the sky. The Da Vinci Glow is waiting....
http://spaceweather.com/
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