system
Given the following post, respond as if you're commenting on Reddit:
human
How do scientists estimate the number of atoms in the observable universe?

It's often quoted that there are around 10^80 atoms in the observable universe. What kind of method can scientists use to estimate something such as this?
gpt
There are roughly 100 billion galaxies, each with roughly 100 billion stars. A star is essentially a ball of hydrogen weighing about 10^30 kg and a hydrogen atom weighs about 10^-27 kg. Thus the total number of atoms of all those galaxies is about 10^(11+11+30+27) =10^79, give or take a few orders of magnitude.

This is a very rough estimate, although famed astronomy Arthur Eddington claimed it was exactly 136x2^256 . Nobody took that seriously.