Earth and Space

Eddington numbers

Stories from Physics for 11-14 14-16 IOP RESOURCES

In astrophysics, the Eddington number is the number of protons in the observable universe. He defined it as NEdd= 136 x 2 256 which is approximately 1.575 x 10 79.

In addition to his scientific studies, Eddington was a keen cyclist, a hobby which led to his proposal of a different kind of metric. A Google search is more likely to bring up the Eddington number as the number of times a cyclist has cycled a particular distance in miles. For example, an Eddington number of 20 would indicate a cyclist had cycled more than 20 miles on 20 occasions.



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