How do we know what stars are made of?

“Not only is the Universe stranger than we think, it is stranger than we can think.” 

Werner Heisenberg.

Almost 150 years ago, the Brazilian social philosopher Auguste Comte, whose words ‘Ordem e Progresso’ (Order and Progress) are enshrined on the Brazilian flag, made a foray into the world of astronomy by stating that ‘man would never know what stars are made of because they are so far away.’ And yet the sciences of physics and astronomy soon proved his assertion wrong.

Scientists already knew that if they took light from distant stars and passed it through a prism they could observe a rainbow interspersed with strange ghostly lines, which they later called spectral lines. Without being able to touch the stars that are billions and billions of miles from earth, they discovered that every element has its own pattern of spectral lines. Each element in that star essentially has its own unique fingerprint.

This science of spectroscopy has allowed us to discover many things about the universe, and we can tell with remarkable detail the composition of stars that are billions of light years away. This technique also allowed us to prove beyond a doubt that the universe is expanding and that expansion is accelerating at a significant rate.

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