December 28, 2008
image by Juerg Alean, Switzerland
The Moon and Earth. Juerg's image captures the essence of Earth - water and air, and these two permit life, which is represented by microscopic plankton in the seawater and the photographer himself. Why are these two near neighbors so different? Gravity and its instantiator, mass. The Moon is so small that any surface or atmospheric water that ever existed there (from comet impacts, for example) can not be gravitationally held permanently. The lack of atmosphere itself makes the Moon inhospitable for retaining additional gas because there is no atmospheric pressure and no reflective clouds to reduce surface temperature. High temperature, no pressure and low gravity allow gases to rapidly dissociate to their component atoms which escape to space with a time scale inversely related to their mass. A significantly more massive moon would retain an atmosphere - Titan is the best example in our solar system.
Juerg writes: On a containership trip from the Mediterranean accross the North Atlantic to New York we were pleased to encounter not only storms, but also remarkably calm days and nights. These were special moments when the ship moved forward silently without the slightest hint of rolling. So flat was the sea that the moon and brightest stars caused mirror images in the water. The photo attemps to convey the serene atmosphere aboard during such nights. DSL photo exposed approx. 5 sec
More on crossing the Atlantic by containership (in German).
Yesterday's LPOD: Happy Birthday Johannes
Tomorrow's LPOD: Two Domes & Two Rilles