## How Many Atoms

People are made up of atoms - mostly oxygen, carbon, hydrogen, nitrogen - arranged into molecules, some very big and some self replicating. Typically these atoms have about 10 neutrons or protons, each with a mass of

\[1.66 \times 10^{-27} kg\]

, so have a mass of about \[1.66 \times 10^{-26} kg\]

.The number of atoms in a human body is then about

\[\frac{85}{1.66 \times 10^{-26}}=5.1 \times 10^{27}\]

.If this sounds big, it is only a tiny fraction of the number of atoms in the Earth. The Earth has a mass of about

\[5.98 \times 10^{24} kg\]

, so there are about\[\frac{5.98 \times 10^{24}}{1.66 \times 10^{-26}}=3.60 \times 10^{50}\]

atoms in the Earth.The Sun has a mass of about

\[1.99 \times 10^{30} kg\]

, so there are about\[\frac{1.99 \times 10^{30}}{1.66 \times 10^{-26}}=1.20 \times 10^{56}\]

atoms in the Sun.These numbers all shrink compared to the number of atoms - mostly hydrogen in the Universe, believed to be about

\[10^{79}\]

.