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.



Limit Less Campaign

Support our manifesto for change

The IOP wants to support young people to fulfil their potential by doing physics. Please sign the manifesto today so that we can show our politicians there is widespread support for improving equity and inclusion across the education sector.

Sign today