Monday, January 12, 2009

The luminous Earth

Last evening we watched the just past full Moon rise majestic and golden out of the sea, preceded by a lunar dawn, something we never see in New England where ambient artifical light blots out all of night's faint treasures.

One of the earliest travelers to the Moon was a Spaniard named Domingo Gonsales who -- in a book published in 1638 by Francis Godwin, called "Man in the Moone" -- winged his way there and back by attaching himself to a flock of wild swans.

Twelve days after taking leave of Earth the birds deposited Gonsales on a high lunar hill, where he began to take note of the incredible sights of his new world. Not the least of the wonders was the Earth, suspended like an ornament in the lunar sky.

Only the Apollo astronauts have observed what Godwin imagined, but most of us have seen photographs of Earth from space, surely among the most beautiful artifacts of the 20th century. The photographs show the planet in all its phases -- crescent, half, gibbous, full -- confirming spectacularly what every schoolchild learns: The Earth shines only by reflected sunlight (some of it previously reflected from the Moon).

Or does it? Even Domingo Gonsales, on his swan-assisted journey, might have looked back and observed the Earth shining by its own light, and since his time the self-luminosity of our planet has increased dramatically.

The planet has many sources of light that illuminate its night side. Lightning storms, volcanic eruptions, and naturally-ignited fires all glimmer in the darkness. It has been estimated that something like 100 lightning strokes per second occur over the Earth's surface, flashing like fireflies. Auroras illuminate vast tracts of terrestrial night.

Life too adds emanations to the planet's aura. Glowworms, luminescent toadstools and flashlight fish, light-emitting plankton and bacteria, all combine protein with oxygen to radiate a cold biological light. But of Earth's living creatures, one contributes overwhelmingly to the planet's self-luminosity. The artificial aurora of Homo sapiens is easily visible from space.

Looking back at Earth today, space traveler Gonsales would see a planet glowing far brighter than the one he saw in 1638. To a large extent it glows with the luminosity of waste. The prodigious burning of tropical forests and oil-field waste gas bodes ill for the planet's fragile atmosphere, and every lumen of energy from electric lights cast upwards into space serves no useful purpose on Earth. Our intemperate, will-o'-the-wisp planet glows wastefully brighter all the time.