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  how does a solar eclipse occur?
  what's a solar eclipse like?
  Bailey's beads and crescent Suns
  annular solar eclipses
  lunar eclipse
  do we have to wait for an eclipse?
  total eclipses that changed the world
  what can we learn from eclipses?

how does a solar eclipse occur?

 

It’s all down to a bit of a coincidence really. When the Moon passes directly between the Earth and the Sun, it appears just big enough to block all the Sun’s disk from our view.

 
 

The Earth, Moon and Sun are not to scale in this diagram. The Moon is actually 400 times smaller than the Sun, but is also 400 times closer to the Earth than the Sun. This would be impossible to draw!

 
You can see more movies in our Gallery [Movie file 1mb or more - High quality]

 

Here’s a movie showing the solar eclipse shadow. It is cast by the Moon onto the surface of the Earth.

         
         

As the diagram above shows, there is a large area surrounding the dark central shadow, the umbra, which is in partial shadow. This area of partial shadow is known as the penumbra and is much larger (about 7,000 km across) than the umbra. If you were standing in the penumbra you'd only see part of the Sun covered by the Moon. What you see depends upon where you are standing when the solar eclipse happens. This diagram gives examples of this:

     

 

From these diagrams you can see that during a total solar eclipse not all the Earth is plunged into darkness. The umbra, the full shadow, is really quite small, and is never more than 268 km across. This means that the chance of any one place on Earth falling under the umbra is also small. Even though a total eclipse occurs somewhere every year or two, it isn't likely to be where you live. A bit like the lottery - someone, somewhere usually wins the jackpot, but it isn't someone you know!

     
 
 
     
     
     
     
   

 

   
 
 

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