The Mudcat Café TM
Thread #109490   Message #2290144
Posted By: GUEST
16-Mar-08 - 08:00 PM
Thread Name: BS: Half moon - science question - ???
Subject: RE: BS: Half moon - science question - ???
"Does it seem odd to anyone else but me that the moon rotates at exactly the same rate as it orbits the Earth, thus always presenting the same side of the moon to our vision? Quite a coincidence!"
Hey LH, Bill D's reference may not be the whole story. It also seems that there is uneven mass distribution with the globe of the moon; this was demonstrated by analysis and the difference between the expected and actual velocities of the various Apollos and other spacecraft as they orbited the moon. These Mass Concentrations, or Mascons, made the capsule speed faster, of sometimes slow down. This was a separate effect from speed changes caused by Kelperian motion.
The far side of the moon (not dark side, that's a great stoner recording) has substantially more craters that then "our" side. Our side has huge "seas"(the dark spots in the surface of lovely Luna) all across the surface. These were at one time great lakes of molten rock that welled up from the core as the moon was being subjected to insane levels of meteor bombardment during the period after it was ripped from the Earth when our Terra Infirma was hit by a mass about the size of Mars.
The lava lakes cooled to form great swathes of the closer side with greater density than the average surface material. The Earth was also hit with about the same violence, but the evidence has been mostly eroded by erosion and geologic subduction.*
This mass tends to keep itself pointed in our direction because of the greater effect that the earth's pull exerts on the mass of the close side.
The Moon certainly had a different rotational period a VERY long time ago. The coupling effect forces eventually put the moon in sync with the Earth. It also changed the length of the day to 24 hours. At one time the cooling molten Earth spun at a very different rate (about 30 hours, as I recall. Don't quote me).
If you are VERY unlucky, some other smart-ass will complicate the matter even further by discussing how interconnected gravitation fields of orbiting bodies result in various LaGrange Points.
* for a view of one very large impact crater in your own Canada,eh, just have a look at the notch cut out of the South-East shore of Hudson's Bay. There are many others on the general area, but this is easy to spot on any map.