Edwin Hubble and the 1923 Discovery of Andromeda Star V1
The Andromeda galaxy is the nearest major galaxy next to our own Milky Way, making the association natural. A little over 100 years ago, however, nobody would have filled in the blank with the word galaxy during ongoing debates about spiral nebulae. American astronomer Edwin Hubble settled that debate with the discovery of a Cepheid variable star known as V1, opening the door to an expanding universe.
The 100-Inch Hooker Telescope Observations at Mount Wilson
Back in 1923, Hubble spent several months scanning Messier 31, or M31, using the 100-inch Hooker telescope at the Mount Wilson Observatory. Andromeda spanned five feet long along the focal plane, requiring dozens of photographic glass plates. On October 5, 1923, amid far-from-ideal viewing conditions, a 45-minute exposure revealed three suspected novae.
Henrietta Swan Leavitt and the Cepheid Variable Period-Luminosity Relation
Hubble marked the objects with an ‘N’ on plate H335H, but one star appeared on earlier plates dating back to 1909. It dimmed and brightened too quickly for a nova, leading Hubble to plot its light curve and identify it as a Cepheid variable. American astronomer Henrietta Swan Leavitt had previously discovered that Cepheid periods correlated with intrinsic luminosity in a relationship sometimes called the Leavitt Law, published in a 1912 paper.
Calculating the Distance to Messier 31
Hubble crossed out the ‘N’ on his photographic plate and wrote ‘VAR!’ to mark the variable star. By determining its period and intrinsic brightness, he calculated a distance of one million light-years, placing M31-V1 well outside the Milky Way. By the close of 1924, he had identified 36 variable stars in Andromeda, including 12 Cepheids, refining his distance estimate to 900,000 light-years compared to modern estimates of 2.5 million light-years.
Revisiting V1 with the Hubble Space Telescope
Nearly 90 years after Hubble’s breakthrough, NASA directed the Hubble Space Telescope at V1 during 2010 and 2011. Amateur observers and professional astronomers tracked the star for six months in 2010 to produce a new light curve. This modern observation captured V1 at its brightest and dimmest phases to highlight the enduring relevance of Cepheid variables.
Frequently Asked Questions About Andromeda Star V1
What equipment did Edwin Hubble use to discover V1?
Hubble used the 100-inch Hooker telescope at the Mount Wilson Observatory during his 1923 observations of the Andromeda galaxy.
.JPG "Edwin Hubble used star V1 to place M31 outside the Milky Way")
How far away is the Andromeda galaxy from the Milky Way?
Current astronomical estimates place the Andromeda galaxy at a distance of 2.5 million light-years from the Milky Way, whereas Hubble initially calculated 900,000 light-years based on his 1924 Cepheid data.
Who established the relationship between Cepheid periods and luminosity?
American astronomer Henrietta Swan Leavitt discovered the relationship while working for the Harvard College Observatory, publishing her findings in a 1912 paper.