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  cycling sunspots
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cycling sunspots

 

Galileo argued that sunspots really were features on the Sun rather than small planets passing in front of the Sun. If we jump forward 200 years from Galileo, the story comes full circle. Between 1826 and 1843, a German astronomer called Samuel Schwabe began to search for undiscovered planets. People had known about Mercury, the closest planet to the Sun, since ancient times, but Schwabe wanted to see if there were any other planets even closer to the Sun than Mercury.

 

Schwabe carefully observed the Sun and recorded the number and position of every sunspot he saw. He didn’t find any new planets, but what he did find was an even more important result.


Schwabe found that the number of sunspots changed over the years in a very regular way. He found that every 11 years the number of sunspots grows from small to large and then goes back to small again. This is now known as the solar cycle.


You can see the solar cycle in this graph, which shows the number of sunspots visible from about 1900 onward. Down Arrow

Samuel Schwabe

Samuel Schwabe (1789-1875), courtesy of Museum für Stadtgeschichte

     
Annual Sunspot Numbers 1900-2000  

Left Arrow Notice that the maximum number of sunspots in each peak changes.

     
Question 1

Answer 1
Quick Quiz
Question 2

Answer 2
 
       
     
Mercury transit

On 15th November 1999 Mercury passed between the Sun and the Earth. Here are some images taken by TRACE as Mercury passed by.

 

It would be easy to confuse it with a sunspot, wouldn't it?

 

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

Take a look at this movie of Mercury going past the Sun.

Observing the Sun to try and find more planets was a really difficult thing to do because Mercury was smaller than some of the sunspots!

   
   

 

   
 
 

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