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WonderAstronomy biography fact

In 1912 Henrietta Swan Leavitt found that certain pulsing stars, called Cepheids, take longer to brighten and dim the brighter they really are. That rule turned them into cosmic measuring sticks: by timing a Cepheid, astronomers can work out how far away it is.

Henrietta Swan Leavitt

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The story behind the card

Leavitt joined Harvard College Observatory in 1893, at first as a volunteer, as one of the women known as 'computers' who measured stars on photographic plates for low pay. Studying the Magellanic Clouds, two small galaxies whose stars all lie at roughly the same distance from us, she catalogued 1,777 variable stars. Because they were all about equally far away, a Cepheid that looked brighter really was brighter, which revealed the link between brightness and period. Once others had measured the distances to a few nearby Cepheids, the rule could be used anywhere. In the 1920s Edwin Hubble used it to show that the Andromeda nebula lies far outside the Milky Way. Leavitt died in 1921, before the importance of her work was widely recognised.

Türkçe oku
Henrietta Swan Leavitt 1912'de, düzenli aralıklarla parlayıp sönen Sefeid yıldızlarında bir kural buldu: yıldız gerçekte ne kadar parlaksa, döngüsü o kadar uzun sürüyordu. Bu kural Sefeidleri gökyüzünün cetveli yaptı; döngüyü ölçen gökbilimci, yıldızın ne kadar uzakta olduğunu hesaplayabilir.

Leavitt 1893'te Harvard Gözlemevi'ne, önce gönüllü olarak, fotoğraf plakalarındaki yıldızları düşük ücretle ölçen ve “hesaplayıcılar” (computers) diye anılan kadınlardan biri olarak katıldı. Bütün yıldızları bize aşağı yukarı aynı uzaklıkta bulunan iki küçük galaksiyi, Macellan Bulutları'nı inceledi ve 1.777 değişen yıldızı kataloğa geçirdi. Bu yıldızlar aynı uzaklıkta olduğu için daha parlak görünen bir Sefeid gerçekten de daha parlaktı; parlaklıkla döngü süresi arasındaki bağ böyle ortaya çıktı. Başka gökbilimciler yakındaki birkaç Sefeidin uzaklığını ölçünce kural her yerde kullanılabilir hâle geldi. Edwin Hubble 1920'lerde bu kuralla Andromeda bulutsusunun Samanyolu'nun çok dışında olduğunu gösterdi. Leavitt, çalışmasının önemi geniş çevrelerce anlaşılmadan, 1921'de öldü.

Sources and further reading

Background reading: Henrietta Swan Leavitt
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