april: the ecliptic plane

This image, taken by the lunar probe Clementine, shows an interesting relationship between the Moon and the other members of the solar system.

The glow in the left-hand limb of the Moon is the Sun's corona. Continuing left we see the planets Saturn, Mars and Mercury. The illuminated area of the Moon shows us the direction of the Earth, off-stage to the right.

The fact that all of these bodies are in a nearly straight line is no coincidence, but results from their being formed billion of years ago from a single spinning disc of dust and gas. Almost every planet, moon and asteroid lies in a shared plane (the plane of the ecliptic) and most revolve and spin in the same direction (anticlockwise as seen from above the north pole).

Image: Clementine Project.