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 ```Is there an easy way to find out (or calculate as function of size, density, distance from Sun etc.) the number of attoms in each of the planets in our solar system. I uderstand that the total number of visible baryonic matter atoms in the universeis less than a google 10e100.```
 ```Easy (but aproximate) way to determine number of atoms in solar system planets is to divide mass of a planets by mass of an atom. Masses of the planet are easy to find, e.g. here: http://en.wikipedia.org/wiki/Planet_(Table) Mass of the 'average' atoms is ranging from H (hydrogen) to let's say Fe (Iron) and Uranium U and are listed here http://periodic.lanl.gov/default.htm It ranges from 1 to 238 times mass of proton proton mass = 1.67262158 × 10-27 kilograms (google search term) Since most of the mass is in the Gas Giant planets Jupiter, Saturn, Uranus, and Neptune, as the following graph indicates. http://csep10.phys.utk.edu/astr161/lect/solarsys/scale.html It is possible to take 'average mass of atom' to be that of H , ( that is of a proton ). More accurate determination would separate 'inner planets' called the "terrestrial" planets because of their proximity to Earth ("Terra" in Latin) and their similarity as solid bodies with compact, rocky surfaces. http://www.solstation.com/stars/4planets.htm The question of the number of atoms in the universe , or just a galaxy, would be much more complex, since there are open questions, about the size of the universe, and so called 'dark mass'. http://en.wikipedia.org/wiki/Dark_matter Sir Arthur Stanley Eddington, ( 1882 ? 1944) an astrophysicist of the early 20th century was first to try to estimate 'number of atoms in the universe. http://en.wikipedia.org/wiki/Arthur_Stanley_Eddington It is called Eddington_number and not taken seriously any more: I believe there are 15,747,724,136,275,002,577,605,653,961,181,555,468,044,717,914,527,116, 709,366,231,425,076,185,631,031,296 protons in the universe and the same number of electrons." So wrote the English astrophysicist Sir Arthur Eddington in his book Mathematical Theory of Relativity (1923) which is .5* 3.149544...×E79 http://www.daviddarling.info/encyclopedia/E/Eddington_number.html No more respected are some more recent speculations I did this calculation, which was relatively simple. You take, first of all, the observed density of matter in the universe, which is roughly one hydrogen atom per cubic meter http://www.kurzweilai.net/meme/frame.html?main=/articles/art0530.html? Hedgie```