Archive Home Page Subj: Dark Side of the Moon
94-07-13 12:42:28 EDT
From: Joe Uhrig
I've been respectfully waiting for someone to address the previous post before once again embarking on my quest to find metaphysical mountains within physics molehils :) No reason however why we can't have several questions being addressed at the same time.
Here is a "why" question dating back to the 9th grade, but first some background. The following is from my ever enlightening Grolliers Online Encyclopedia under "MOON" and "SOLAR SYSTEM".
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"The Moon is the only natural satellite of the Earth and a unique member of the solar system in several respects. With a radius of 1,738 km (1,080 mi), it is approximately one-quarter of the size of the Earth and 81.3 times less massive. Although the solar system contains both larger and more massive satellites than the Moon, none except Pluto's moon differs so little from its planet in mass or size. Indeed, the Earth-Moon and Pluto-Chiron systems constitute veritable double planets...."
"...The Earth-Moon system is often referred to as a "double planet" system, because the Moon is more nearly comparable in size to the Earth than the other satellites are to their primaries (except for Pluto and its moon). ... It is one of a group of the six largest satellites in the solar system that have approximately comparable mass, and the only such large one in the inner solar system. Compared to the mass of its primary, the Earth, the Moon is abnormally massive...."
"...In addition to its motion through space, the Moon also rotates about its axis in a period of one sidereal month, so that it keeps approximately the same side toward the Earth at all times. Nonuniformities in its orbital motion, however, together with the inclination of the orbit to the ecliptic, cause "optical librations" that allow 59% of the entire lunar surface to be seen from the Earth at one time or another. The remaining 41% was hidden until the Soviet LUNA 3 spacecraft photographed the far side in October 1959. It has since been thoroughly mapped...."
"...For many years three theories about the formation of the Moon were supported by various groups of astronomers. The fission theory held that a piece of the rapidly-spinning molten Earth was flung into space. The double planet theory proposed that the Moon formed independently of the Earth from the primordial cloud. The capture theory held that a body from elsewhere in the Solar System passed near the Earth and was captured by the Earth's gravitational forces. The Apollo space program and Moon landings failed to confirm any one of these theories...."
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According to the recent Scientific American, scientists are now leaning towards a impact theory of formation.
The "dark side of the moon" is certaintly a cultural metaphor with metaphysical implications. There is of course no "dark side of the moon" , just a "far side" we can't see from earth (and according to some theories it's inhabited by cartoonists).
My question is this. Why can we only observe 59% of the moon from earth. Recognizing that our observational data on moons is pretty much limited to this solar system, is there anything inherent in the physics of orbiting bodies that would cause this or is this a "statistical anomoly"?