We began by talking about whether an Oxygen atom in Kerala is identical to an Oxygen atom in Kashmir. In fact, all Oxygen atoms anywhere in the Universe are exactly identical! This is an amazing fact: Even though in ordinary life, we don't experience even two objects that are exactly identical, each atom has billions of other atoms that are identical to itself.
This is how scientists can talk about properties of stars that are billions of kilometres away. Because atoms are identical everywhere in the Universe, learning atoms' behaviour here on Earth helps us understand properties of faraway objects.
Check out the next module in this series! Structure of the Atom 1