“The astronaut decided to give the aliens some space.”
First Cepheid photographed in AndromedaIn 1923, Edwin Hubble photographed part of the Andromeda nebula. By 10 Oct 1923, he identified it as showing a faint variable star. On the plate, he crossed out his earlier “N” mark for a nova, and put in large letters, “Var!” for variable. This was a notable discovery. By early next Feb, he had measured the star's changing brightness. This confirmed it was a Cepheid variable star, the first found in the Andromeda nebula. Now he had a way, for the first time, to reliably measure the distance to Andromeda. The rate of variation of a Cepheid identifies its absolute intensity. By comparing that calculated quantity with the observed apparent intensity, the distance could be inferred. Andromeda was far beyond the Milky Way. After getting more data. he notified an AAS meeting with a paper read 1 Jan 1925.« |
