Sunday, 15 February 2009

The Da Vinci Glow

The other name for Earthshine is the "Da Vinci Glow" (or "the old moon in the new moon's arms"). Leonardo Da Vinci, the man who invented, well, sort of everything, died before our old friend Copernicus put forward his heliocentric theory of the Solar System. But this didn't stop him suggesting a theory (not just a theory, but the almost perfectly correct theory) for the appearance of light on the dark section of moon at sunset.

Earthshine was a riddle. How could we see a fingernail of beaming brightness on this dull, ashen orb? In fact, why could we see the rest of the orb at all? In a selection of Da Vinci's scientific writings named the Codex, the great innovator describes how sunlight reflects off Earth's oceans onto the lunar surface.

"...this brightness at such a time being derived from our ocean and the other inland seas -- for they are at that time illuminated by the sun, which is then on the point of setting, in such a way that the sea then performs the same office for the dark side of the moon as the moon when at the full does for us when the sun is set..."
Codex Leicester

He almost got it. The Apollo astronauts (this is over 400 years later we must note) observed how clouds are actually the better reflectors of sunlight. They appear bright where the seas look dark. But not a bad attempt for a man without a telescope.


anil gupta said...

what an outstanding insight, keep it up


rob-sp said...

Many thanks, Anil. What a fascinating organisation the Honeybee Network seems.

The Shodhyatra - a fantastic enterprise.