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.

So Cepheids act as 'standard candles'.


Measuring a Cepheid's 'pulsation time' tells astronomers how bright it really is.

By comparing the 'true brightness' with how bright it appears, they can work out how far away it is.

                                 

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