Cepheid Variables Discovered in Andromeda Galaxy
In 1923, Edwin Hubble was examining photographic plates of the Andromeda
Nebula M31, taken with the 100-inch telescope in order to find novae --
stars that would suddenly increase in brightness (because of cataclysmic
explosions).
On this place from the night of October 5-6, 1923, Hubble located three
novae, each marked with an "N." One of these novae, however, turned out to
be a Cepheid variable, a star that changes predictably in brightness, and the
"N" was crossed out and the star was relabeled "VAR!" This Cepheid, and
others subsequently discovered in the Andromeda Nebula, enabled Hubble to
prove that the Nebula was not a star cluster within our own Milky Way, but a
galaxy more than a million light years away.
From:
Mount Wilson Observatory History page
This image was featured as Astronomy Picture of the Day April 6 1996
Image also available as positive (JPG)
[or PNG]
Hartmut Frommert
(spider@seds.org)
Christine Kronberg
(smil@lrz.uni-muenchen.de)
Last Modification: 2 Jul 1999, 23:30 MET