TOTAL MOON ECLIPSE DECEMBER 10, 2011

Well it is true that there will be a total eclipse of the moon on December 10th of this year but unfortunately for us around the LASS site it is going to be a short look.  The penumbra stage will begin at 5:33 AM (plus or minus a minute of two) and the moon will set in the west (where else does the moon set?)  at about 6:45 AM.  The moon will not be in a total eclipse until 8:06 AM. It will already be below the western horizon from our viewing point by that time so we won't see the whole eclipse. 
I know that most of you that read this blog know that a lunar (moon) eclipse can only happen during or very near the full moon phase.  That is the only time that the earth could possibly be positioned between the Sun and the moon. Technically, it would be possible to have a full lunar eclipse every month but in actually it only happens about twice every year.  And even then it isn't visible to everyone.  It is a little difficult for me to explain this since I can't easily use my hands to illustrate all the many in's and out's of a lunar eclipse in this blog but a casual glance at the illustration here will give you something to hang onto while I attempt to explain the phenomenon. 

Under the conditions shown at the left, the moon is in the full shadow of the earth and therefore is in a full eclipse, at least to folks in some parts of the world. Needless to say, if you can't see the moon at all because it isn't visible to your location during the time that it is in the earth's shadow, you aren't going to see any part of the eclipse. That is the case on the Dec 10th eclipse for us in the Texas area of the U.S.  For us, the eclipse begins early in the AM hours of the 10th and it just so happens that the moon will be setting in the west from our viewpoint at that time of the morning.  We will be able to see part of the earth's shadow as it covers the moon but only for a short period.  If you are lucky enough(?????) to live in Calif you could see the entire eclipse.


Since we have been talking about a "full eclipse", someone might want to know what other kinds of eclipses are there out there?  Simply stated, there is either a full eclipse or a partial one. The partial one could be anything just short of the moon being in the full shadow of earth to something as slight as just what we might call a slight brush.  What then is the thing that prevents all eclipses from being the full blown thing? 

Without trying to get to technical, here is the simple explanation. During its orbit of the sun, the earth follows a path called the "ecliptic". Since the moon is a satellite of earth, it also follows this "ecliptic" with a slight variation.  That variation amounts to approximately 5 degrees variance from that of the earth's ecliptic. Looking at the sketch above, you can see that there is an intersecting line between the earth's ecliptic and the moon's orbit around the earth. The point of this intersection is called "Nodes" and there is a northern and a southern node. In order to have any kind of lunar eclipse the moon must be at the northern or southern node and at the same time the earth must be between the moon and the sun.  It stands to reason that there is always a shadow effect from the sun/earth relationship ( how else could day and night be possible?) but unless there is some object for that shadow to fall upon we only recognize it as night time. The moon does make this critical shadow alignment on the average of every six (6) months hence a lunar eclipse every six months. Sometimes the alignment isn't always perfect therefore we see only a partial eclipse. Always keep this fact in mind---if your can't see the moon from your vantage point when it goes thru all these gyrations, you will not see the eclipse.


 If all of this confuses you just come to one of our LASS observing parties.  I can demonstrate the entire process to you in 3 minutes using a couple of balls and a flashlight. If you need a fully scientific explanation, Google "lunar eclipse" and follow the various articles.  HAVE FUN