In the early 1900s, most astronomers mistakenly believed that 66 percent of the sun's substance was iron.
Topic
How Cecilia Payne discovered the sun is mostly hydrogen and helium — and why her contemporaries resisted her finding.
Framework
Highlight Noteworthy. The author tells the story of Payne's pioneering discovery and the resistance it faced.
Main Point
Cecilia Payne pioneeringly argued the sun is mostly hydrogen and helium (not iron). Her finding was substantiated but resisted because contemporaries had no accepted explanation for how hydrogen and helium could produce the sun's energy. Once nuclear fusion was understood, her result was confirmed.
P1: Payne's claim
Most early-1900s astronomers thought the sun was 66% iron. As a graduate student in the 1920s, Payne argued the sun is mostly hydrogen and helium. Her claim, ultimately accepted, met strong resistance.
P2: Why the iron view held
Earth and asteroids contain iron; spectroscopy seemed to support iron in the sun. But how could iron produce the sun's energy? Lord Kelvin's contraction hypothesis required the sun to be only ~20 million years old — but fossil records suggested billions of years. For Payne, this meant the iron hypothesis (and the spectroscopic evidence behind it) had to be reexamined.
P3: Payne's reanalysis
Payne suspected preconceptions had skewed how the spectroscopic data were read. Analyzed without preconceptions, the data showed 90% hydrogen, most of the rest helium, and some iron and other elements. Most astronomers dismissed her interpretation; some explained it away by claiming she had only examined data about the sun's outer surface, not its interior.