Bringing the Joys of Astronomy to the Public Through Awareness, Advocacy, and Education

The Moon - Earth’s Largest Satellite

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A sliver of a moon as imaged by Don Brown of Utah SkiesThe Moon will be new on the 26th. Those observers that consider the moon “light pollution” look forward to this time of thesynodic cycle as the moon travels with the sun, keeping the night sky dark,  favoring views of distant, elusive, and faint fuzzies - galaxies, nebulae, and clusters. 

Remember, as the moon waxes and wanes, you can look forward to those phases where Moon observations are most fascinating. Features appear - mountains, craters, rilles - as the sunlight casts long, defining shadows. Look along the portion of the Moon separating light from dark, known as the terminator, for the greatest contrasts.

Fact & Figures

The Moon, unlike other more esoteric and distant astronomical objects, has no named discoverer. Or, one could say that we’ve all discovered the most familiar of heavenly bodies. Cultures over the ages have created lore of the Moon; mythology is rich for this closest celestial neighbor, as are explanations for its place in the sky.

There are several scientific theories explaining the origin of the Moon. An early theory proposed that the Moon was formed at the same time as the Earth, making it a sister body. This theory, however, cannot explain why the Moon lacks iron. A second idea was that the Moon was formed somewhere else in the solar system where iron was scarce, but this theory, too was discredited when lunar rocks were analyzed and shown to be very similar to Earth’s. A third theory suggested that the Moon was spun-off from the Earth as it was forming. While this would explain the similar compositions, a study of the total angular momentum of the Earth-Moon system indicates that the system could not have formed like that. The theory most widely accepted today was first proposed by Dr. William K. Hartmann and Dr. Donald R. Davis of the Planetary Science Institue in 1975 (Hartmann, W. K. and D. R. Davis 1975 Icarus24, 505.) Their theory states that very early in the Earth’s formation, a rogue body impacted the infant Earth, blowing out debris. This debris remained in orbit around the Earth and eventually came together to form the Moon.

  Max Mean Min
Angular Size 33.14 ‘ 31.09 ‘  29.04 ‘
Distance from Earth   384,467km  
Mass 0.07349 x 1024kg  (0.0123 x Earth)
Size 1738.1km @ Equator  (0.2725 x Earth)
Revolution period 27.322 days
Synodic period 29.53 days
 
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