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Author Topic: lunar eclipse, the frequency of  (Read 3300 times)

paul.fr

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lunar eclipse, the frequency of
« on: 10/11/2007 20:14:50 »
If the moon orbits the earth on a monthly basis, why do we not have an eclipse every month?


 

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lunar eclipse, the frequency of
« Reply #1 on: 10/11/2007 21:56:00 »
Because the moon's orbit is slightly inclined with respect to the earth's orbit around the sun.  There are two places where the planes of the earth and the moon's orbits intersect these are called the nodes.  It is only when full moon occurs when the moon is close to one of these nodes that an eclipse of the moon can occur.  This is similarly true for new moon occurring and resulting in an eclipse of the sun.  There are therefore two periods each year when eclipses of the moon and the sun are likely.  The nodes of the moon's orbit gradually move with time completing a full circuit about every 19 years so eclipses gradually move through the year and tend to repeat in a regular pattern every 19 years.  The ancient Greeks knew about this and could predict eclipses reasonably accurately.  I also have predicted eclipses back in the 1950s based on information given in  the Nautical Almanac and a book Called Practical Astronomy by  W Schroeder.

There are typically 4 eclipses a year two of the moon and two of the sun and in 2008 they will happen in February and August.
 

paul.fr

  • Guest
lunar eclipse, the frequency of
« Reply #2 on: 11/11/2007 00:44:22 »
excellent, thanks Ian
 

lyner

  • Guest
lunar eclipse, the frequency of
« Reply #3 on: 11/11/2007 00:45:36 »
If you want to cast a shadow with a small object, you have to get it just right. There are a lot of possible paths around the Earth and around the Sun that don't get it right.
 

paul.fr

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lunar eclipse, the frequency of
« Reply #4 on: 11/11/2007 01:20:13 »
Andrew,
I cast a shadow wherever I go!
 

lyner

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lunar eclipse, the frequency of
« Reply #5 on: 11/11/2007 18:18:09 »
OK -with a small object ON a small object!!!
God, they're soooo picky on this forum.
I am for ever in your shadow. 4000+ posts!!!!
 

paul.fr

  • Guest
lunar eclipse, the frequency of
« Reply #6 on: 11/11/2007 18:41:49 »
but whoever said quantity related to quality?
 

The Naked Scientists Forum

lunar eclipse, the frequency of
« Reply #6 on: 11/11/2007 18:41:49 »

 

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