"Silent Sky" is the name of a play by Lauren Gunderson that tells the somewhat fictionalized story of the life of Henrietta Swan Leavitt. The play is currently being performed this season at the Creede Repertory Theatre.
Leavitt worked at the Harvard College Observatory in the early 1900s and is famous for discovering the correlation between the intrinsic brightness and the pulsation period of a type of variable star known as Cepheids. This relationship was the key toward understanding the size of our galaxy, the distance to other galaxies, and the size of the universe. Leavitt would have been a strong contender for the Nobel prize had she not died of cancer at the age of 53.
Put simply, if two Cepheid variables with the same pulsation period are observed and one is four times fainter than the other, then the inverse-square law says that the fainter star must be twice as far away. If the distance to the nearer star can be determined, then the distance to the further star is also known. By measuring the apparent brightness and pulsation period of Cepheids in other galaxies and comparing them to those in our galaxy, we can determine the distance to the other galaxies. This was first accomplished by Edwin Hubble in 1924.
The two closest Cepheid variables are Polaris, the North Star, and Delta Cephei, from which the type-name "Cepheid" is derived. The distance to both have now been measured via parallax to an accuracy of about 0.4% for Polaris and 4% for Delta Cephei. Polaris is 447 ly distant, and the distance to Delta Cephei is about 912 ly.
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| The Little Dipper (left) and the constellation Cepheus (right). Polaris and Delta Cephei are marked by circles. |
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| Without the constellation lines. Olympus 17mm f/1.8 lens, Sparke-6 filter. |
These images were obtained on 25 July, the first clear night after a prolonged stretch of rainy weather. The night was breathlessly calm and very dark, with a measured sky brightness of sqml = 21.66 to 21.71 mpsas.
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| The Summer Triangle |
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| The Big Dipper over Bristol Head. |
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