Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site decwrl.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!houxz!vax135!floyd!cmcl2!seismo!hao!hplabs!sdcrdcf!sdcsvax!dcdwest!ittvax!decvax!decwrl!dec-rhea!dec-null!kinmonth From: kinmonth@dec-null.UUCP Newsgroups: net.games.trivia Subject: more on the moon debate Message-ID: <1369@decwrl.UUCP> Date: Mon, 11-Jun-84 17:02:12 EDT Article-I.D.: decwrl.1369 Posted: Mon Jun 11 17:02:12 1984 Date-Received: Wed, 13-Jun-84 02:35:14 EDT Organization: DEC Engineering Network Lines: 47 All this talk about the moon revolving or not has set me thinking. First of all, I should say that I have decided that the moon does indeed rotate on its own axis. My argument (to myself) was something like the following: If an object is rotating on its own axis, then it must have what we commonly call a North pole and a South pole. My definition of a "pole" was as follows: If you have a free-floating body, and there exists a point on that body from which the motion of all other bodies sufficiently distant appears circular, then that point is a pole. Thus if you are standing at a pole of the moon, then other visible bodies of sufficient distance (distance stars for instance) appear to have a circular motion. (of course, a body directly overhead would not appear to move, but that's just a degenerate circle). The "sufficiently distant" part is meant to minimize the effect of the actual motion of the distant bodies. i.e. if they are sufficiently distant and moving at a "reasonable" speed, they they can be considered stationary relative to you over a short time period. Since there are such points on the moon, the moon has poles, or equivalently, the moon is rotating on an axis. This brings me to another question. Can there be a free-floating body which is NOT rotating on its own axis (by the way, isn't "rotating on its own axis" synonymous with "rotating"? If something is rotating, it must be on SOME axis, and why would it be someone ELSE's? Of course it is its OWN axis....). Back to the question. It would seem that all free-floating object must rotate to some degree, no matter how slowly. The odds that something could be floating around prefectly aligned with the universe must be hovering near zero. This made me think of another thing. What are the chances that the period of rotation of the moon is EXACTLY the same as the time for one orbit of the Earth? I cannot imagine that this is a coincidence. The only explaination I can think of is that the side of the moon that always faces the Earth is more dense (perhaps much more?) than the other side. Thus the graviational attraction of this side eventually caused the moon's rotation to stabalize with the "heavy" side towards the Earth. If this were true, note that a rotating moon would appear to wobble. We can't observe this from earth however because we don't see the moon rotating; we always see the same side. There must be some hole in this argument though( i.e. the "heavy sided moon" argument). It seems that surely I would have heard of this unevenness in the moon's density if it were true. Does anyone out there have another explaination for why the lunar day and lunar month are equal? I cannot believe it is coincidence. Bruce Kinmonth ...decvax!decwrl!rhea!null!kinmonth