Cecilia Payne found what stars are made of and was told to hedge
In 1925 a doctoral student at Radcliffe, Cecilia Payne, showed that stars consist mostly of hydrogen and helium, nothing like Earth's rocky make-up. The result seemed so unlikely that her examiners persuaded her to soften the conclusion before publishing. Later research proved she had been right all along.
Her work capped a century-long shift in what astronomers asked. For most of the 1800s the job was measuring positions and computing motions. One of astrophysics' founders, James Keeler, put the new goal neatly: learning what heavenly bodies are, not where they are. That became possible once William Hyde Wollaston and Joseph von Fraunhofer independently noticed dark lines in the spread-out colours of sunlight, and by 1860 Gustav Kirchhoff and Robert Bunsen had matched those lines to particular chemical elements.
The spectrum soon yielded surprises. In 1868 Norman Lockyer saw a yellow line in sunlight that matched no known element and declared it a new one, naming it helium after the Greek word for the Sun. From 1885 Edward Pickering at Harvard set a team of women computers, among them Williamina Fleming and Annie Jump Cannon, to classify stellar spectra from photographic plates. By 1924 Cannon had catalogued over a quarter of a million stars, and her classification scheme became the world standard.
Around 1920 Arthur Eddington guessed that stars shine by fusing hydrogen into helium, releasing energy as Einstein's E = mc2 predicts, well before fusion was understood or anyone knew stars were largely hydrogen. Payne's measurements supplied the missing ingredient a few years later. Older ideas had held that the heavens were made of a completely different substance from Earth, fire for Plato and aether for Aristotle; Galileo, Descartes and Newton argued for shared laws but lacked the tools to prove it.
Today astrophysicists observe across the spectrum, from radio waves that reveal cold gas and the afterglow of the Big Bang to X-rays and gamma rays from black holes and magnetars, which must be caught from space or indirectly. In this century gravitational waves have joined the toolkit.
Source: Astrophysics
