Henrietta Leavitt and the discovery of Cepheid Variable Stars.

Distances in space were largely a mystery at the start of the 20th century.

The distances of some stars had been measured using a method called 'parallax'.



Finding distances of objects far out in space needed a new discovery.



The person who made that discovery was Henrietta Leavitt.

She discovered that certain types of variable stars changed brightness in a regular way.



These pulsating stars are known as Cepheid variables, named after the star Delta Cephei. 

Henrietta Leavitt looked at large numbers of these stars in a feature called the Small Magellanic Cloud, and discovered that brighter Cepheids pulsed more slowly than dimmer ones.

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