SUNSET SKY SHOW: When the sun goes down tonight, step outside and look southwest. You'll find Venus and the crescent Moon beaming side by side through the deepening twilight. Try to catch them before the sky fades completely black. For reasons no scientist can explain, these two heavenly bodies are especially beautiful when surrounded by twilight blue. [sky map]
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.
Wild imagination, however, was one thing Leonardo had in abundance. His notebooks are filled with sketches of flying machines, army tanks, scuba gear and other fantastic devices centuries ahead of their time.
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....
Realtime Space Weather Photo Gallery
REFLECTION RAINBOW: Spaceweather.com reader Chris Erikson was driving to work yesterday when he saw something strange. It was a rainy day on the Columbia River Gorge near the Oregon-Washington border, and a beautiful double rainbow arced across the sky. Suddenly, as passed the riverbank, another rainbow cut across the double 'bow. "I've never seen such a thing before," says Erikson, who snapped this picture through the front windshield:
This is called a "reflection rainbow." To understand where it comes from, remember how normal rainbows form: Sunlight bounces in and out of falling raindrops. Those raindrops act like tiny prisms, spreading sunbeams into their constituent colors. Reflection rainbows form in the same way, except the source of light is not the sun; it's the reflection of the sun from a body of water.
"The sun must have been reflecting from the Columbia River, which was only 200 feet to my left," says Erikson. "Here's a map showing where I was."
Rainbows come in a variety of forms. The reflection rainbow Erikson photographed is just one of many you can see if you are alert for the unusual. Start looking here.
Realtime Space Weather Photo Gallery
BUY A TICKET TO THE EDGE OF SPACE: Christmas shopping for a young scientist? Consider this: For the holiday season only, we're reducing the cost of payload space on Earth to Sky Calculus balloons from $500 to only $299.95. Buy an edge of space gift certificate before Dec. 25th and your student can send an experiment, photo, or keepsake item to the stratosphere, completely supported by an Earth to Sky Calculus launch and recovery team.
This is not only a great Christmas gift, but also a good kickstarter for science fair projects. Experiments will be flown and returned along with video footage, GPS tracking, temperature, pressure, altimetry and radiation data.
To take advantage of the discounted rate, payment must be received before Dec. 25th. However, the flight can take place at any time in the next 12 months.
Conditions: No mammals. Plants and non-pathogenic microbes are allowed. Generally speaking, experiments should weigh less than ~300 grams and occupy a volume less than ~64 cubic inches. A Skype brainstorming session is included with each certificate. Dr. Tony Phillips and other members of the Earth to Sky team will chat with students to help them craft an experiment that will work in the harsh environment of the stratosphere.
More edge of space Christmas gifts may be found in the Earth to Sky Store.