Originally Posted by
CameronBornAndBred
Seems like a pretty rough neighborhood to set up your alien base.
Found this interesting bit on Wiki, which lessens the "shield" theory.
It goes on to speculate that heat from Earth may also be responsible. (A long, long, long time ago...not now.)
https://en.wikipedia.org/wiki/Far_side_of_the_Moon
Interesting wikipedia article. Not sure of the source of the information, but seems mostly sound.
Pictures from the moon of the "Big Blue Marble" suggest that space rocks coming in at very high speeds, to the Near Side of the Moon, are likely to escape Earth's gravity to reach the moon or slip past. Speeds as much as 10kMPH-18kMPH could elude the Earth, but they would have to be at an oblique angle. From time to time we hear about those rocks that pass between the moon and the earth, and they are moving really fast (almost perpendicular to the line between the Earth and the Moon); they have to be!
But if it is moving slower, and it is coming from behind the Earth (The Earth being 81 times the Mass of the Moon) it is likely going to hit the Earth (and atmosphere). IMHO. That's what planets do (by definition).
I'm not sure why the 4% number is given with an area calculation ( NASA calculates that the Earth obscures only about 4 square degrees out of 41,000 square degrees of the sky as seen from the Moon) only; there is no momentum/gravitational component to determine an expanded Cross-section that would expand on the effective area of capture that an incoming meteor/object would experience (depending on the vector momentum [angle, mass, speed]). Cross-section is how the High-Energy/Nuclear guys calculate the size of things they bombard and that is based on the momentum and exact direction of the bombarding particle; whether there is an attractive (gravity) or repulsive (charge) force that changes the calculation, the equations would be essentially the same, it just grows or shrinks the cross-section.
An aside, on a common unit of cross-section (Area of the target being shot at) for atomic/High-Energy research, the Barn:
During Manhattan Project research on the atomic bomb during World War II, American physicists at Purdue University needed a secretive unit to describe the approximate cross-sectional area presented by the typical nucleus (10−28 m2) and decided on "barn". They considered this a large target for particle accelerators that needed to have direct strikes on nuclei, and the American idiom "couldn't hit the broad side of a barn" refers to someone whose aim is very bad.[2] Initially they hoped the name would obscure any reference to the study of nuclear structure; eventually, the word became a standard unit in nuclear and particle physics.
https://en.wikipedia.org/wiki/Barn_(unit)
Those wacky physics guys.
Larry
DevilHorse