Cecilia Payne-Gaposchkin stars hydrogen helium composition 1925

Astronomers once resisted the idea that stars are mostly hydrogen

In 1925, Cecilia Payne-Gaposchkin concluded that stars are made mostly of hydrogen and helium. Other astronomers initially resisted the result because they expected stars to have a mix of elements more like Earth's.

Industrialization first lengthened British work hours

In Britain, working hours initially grew longer with industrialization. Political and economic changes over the 19th century eventually brought them back to pre-industrial levels, and sometimes below them, leaving more time for leisure.

Some fish use rocks as anvils

A wrasse can dig up a shellfish, carry it several meters to a rock, and repeatedly smash the shell against the rock with movements of its head. Once the shell breaks, the fish eats what is inside.

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Cecilia Payne-Gaposchkin stars hydrogen helium composition 1925

Astronomers once resisted the idea that stars are mostly hydrogen

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