Nothing like the sun
"My mistress' eyes are nothing like the sun"
- William Shakespeare, Sonnet 130
The moon, Earth's only natural satellite, is incapable of creating its own light and is but a pale reflection of the Sun. Despite only reflecting 12% of the sunlight on average, the moon is the brightest object in the sky second only to the Sun. Interestingly, there is almost no atmosphere to disperse the sunlight so the sky always looks black on moon, even on the bright side.
Although the moon is very close by astronomical standards (238,900 miles from Earth), mankind has only set foot on its surface a total of six times. To give you some idea of how difficult that feat was, consider that only 12 people have ever set foot on its surface.
The first humans ever to set foot on the moon were Neil Armstrong and Buzz Aldrin, on July 20th 1969, during the Apollo 11 mission. The last mission was in 1972.
38 years ago we reached beyond our cosmic cradle, even if only a little, and we haven't been back since. It's a pity, to be sure, but the six Apollo Missions to successfully land and return have contributed greatly to our knowledge of the moon, as well as to its mystery.
Our moon is the 4th largest satellite in the Solar System. With the number of moons out there (60 for Saturn and 63 for Jupiter alone) that's pretty impressive! The only three moons larger than our own are: Ganymede and Callisto (of Jupiter), and Titan (of Saturn).
Although our moon is large compared to other moons, its mass is only slightly more than 1% of Earth's mass. This leads to perhaps one of the most fascinating aspects of the moon's physical characteristics: It seems to be nearly hollow!
The Apollo 12 crew jettisoned the lunar module ascent stage as they left the moon on November 20, 1969. After being jettisoned, the module crashed onto the lunar surface and created an artificial moonquake. Those involved reported "the moon reverberated like a bell for more than an hour."
This effect was repeated with Apollo 13, but on a much larger scale. Seismic equipment recorded reverberations lasting for three hours and 20 minute, and traveling to a depth of 25 miles! This led many to conclude that the moon has an unusually light (or even no) core.
Perhaps due to its lack of a core (or at least lack of a substantial core), there is no geological activity. There are no mountains because there is no continental drift or plate tectonics. The only geological characteristics that do exist are from impact with meteoroids, asteroids, and comets.
The moon is a silent place. There is very little atmosphere for sound waves to travel through. Another result of this lack of atmosphere is that there are no weather systems, so Neil Armstrong and Buzz Aldrin's footprints will remain on the lunar surface for millions of years.
The moon's orbit around the Earth is such that its period of rotation keeps it synchronized with Earth's own rotation. Because of this synchronous orbit with the Earth, we only ever see one side of the Moon. The side we don't see is known as the "dark side of the moon". This is, of course, a misnomer as there is no real dark side, since the Moon revolves around the Earth and the Earth around the sun and there is a night and day on the Moon.
We need the moon; not like we need the sun, but we still gain many benefits from our satellite. For instance, the pull of the moon's gravity is what gives us our tides. But more importantly, the moon appears to have acted as a cosmic protector in the past, shielding our beautiful blue cradle from many an impact.
In 1959, the Soviet spacecraft Luna 3 sent back the first pictures of the dark side of the moon. These photos showed many more craters on the far side of the Moon than the side facing Earth. This is presumed to be due to the moon absorbing meteor, asteroid and comet impacts that would otherwise hit Earth.
I hope I've given you some things to ponder when next you gaze upon our mistress moon.
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