Back to Glossary

The Moon

The Moon is Earth’s only natural satellite—a rocky, cratered body about one‑quarter the diameter of Earth, orbiting at an average distance of approximately 384,400 km. It influences tides, stabilizes Earth’s axial tilt, and was formed about 4.5 billion years ago following a collision between Earth and a Mars-sized object.

Source: science.nasa.gov

APODs including "The Moon"

A Darkened Sky

20/09/2008

A Darkened Sky
Image Credit: Miloslav Druckmuller / NASA APOD

For a moment on August 1st, the daytime sky grew dark along the path of a total solar eclipse. While watching the geocentric celestial event from Mongolia, photographer Miloslav Druckmuller recorded multiple images with two separate cameras as the Moon blocked the bright solar disk and darkened the sky. This final composition consists of 55 frames ranging in exposure time from 1/125 to 8 seconds. It spans nearly 12 degrees, with the relative position of the Moon and Sun corresponding to mid-eclipse. On the left is bright planet Mercury, but many stars are also visible, including the Praesepe star cluster (also known as M44 or the Beehive cluster) in Cancer, above and to the right of the silhouetted Moon. Remarkably, the nearly perfect conditions and wide range in individual exposures allow the composite picture to register the lunar surface and follow the delicate solar corona out to a distance of nearly 20 times the radius of the Sun. In fact, the composite presents a range in brightness beyond what the eye could see during the eclipse.