THE REALLY BIG MOON

Sometimes I think we astronomy observers have a hard time explaining some of the more insignificant events that happen and that are of some importance to us as observers but may or may not be of any consequence to the general public.  Take the recent event when the moon was at its closest point it has been in several years and the fact that it would appear 14 percent larger than usual.  DUH and double DUH. I can't recall how many folks asked me how big the moon would really be and if the fact that it was so close might have been the cause of the earthquake in Japan.


The size of the moon at moon rise is hard to explain other than to say it is an optical illusion and that it is directly related to whatever you might be seeing in the foreground to compare it to.  In other words, the moon rising over the open sea might not look quite as large as the same moon rise if it were observed with buildings or trees in the foreground.  We all have seen photographs that have been taken that would appear as if you were holding a building or statue in your hand.  It all has to do with the perspective and how the camera sees each object.  That is essentially how the moon may look as it begins to rise.  Something in the foreground that we can see and that we know the relative size of gives us the illusion that the moon is quite a bit larger than it really is.  As it get higher in the sky where there is little or nothing to compare it with relative to size, it becomes smaller and smaller.  But I defy anyone to show me that the moon is 14 percent larger than it has been before if for no other reason than we can't remember how large it looked the last time it was full.   In fact I believe if I told someone that the full moon for the next 6 months (or any other time frame you choose) would look "X" amount larger they would believe it really looked larger to them.  But it is an interesting part of astronomy and I think it was worth my time to go out and look even if I couldn't tell the difference.


Now about that question concerning the earthquake in Japan.  The question arose because folks are aware that the moon does have a gravitational influence on earth and that the moon is the primary cause of high and low tide in the oceans.  The notion behind the question was if the moon had that kind of effect of the ocean could it have enough gravitational effect to cause a earthquake.  The simple answer is NO.  Earthquakes are caused by the the shifting of the earths surface and as far as science now understands this movement, gravitational pull is not a factor.  The principal of the shifting of the earth is not easy to understand and is well beyond the scope of this rant to explain but I would offer one explanation that many of us might understand.


I know that all of you readers watch the weather reports and forecast. In the illustration at the left the warm air is sliding up over the cold air which is heavier and dragging along the earth surface as it moves along.  We understand this because we can comprehend and even observe air sliding over or under other air.  It suffices here to say  that the surface of the earth goes thru the same kinds of processes. Sometimes the earths surface slides under other parts, sometimes it just slides along or against another part and sometimes it simply breaks apart.  When these events happen we see the results as earthquakes.  It really isn't as simple as all that but it suffices to say that the gravitational tug of the moon DOES NOT have any influence that would cause earthquakes.


So the next time you hear someone say that several of the planets are going to become aligned at some future date and that the earth will be pulled apart and destroyed, just smile and nod and don't worry.  It ain't gonna happen.  Remember this thought---a little knowledge is dangerous for any of us.  But some knowledge is better than none at all.