> [She] proposed in her 1925 doctoral thesis that stars were composed primarily of hydrogen and helium. Her groundbreaking conclusion was initially rejected because it contradicted the scientific wisdom of the time, which held that there were no significant elemental differences between the Sun and Earth.

I'm reminded of a college lecture one day in a class I took called Physics of Stars. The professor walked up to the whiteboard and wrote:

Elemental composition of the universe:

  Hydrogen and helium   99%
  Oxygen                ~1%
  Everything else      <<1%

That was well over a decade ago, and it blows my mind as much today as it did then.