SUNSET: 
0
Photographer:
Rod Pommier
Location of Photo:
Pommier Observatory, Portland, OR, USA
Date/Time of photo:
August, 2021
Equipment:
Celestron Compustar C14 with Starizona LF reducer/corrector (f/7.5), SBIG STL 11000M CCD with Baader Planetarium LRGB filters, SBIG AO-L adaptive optics at 8 Hz
Description:
The night of October 5/6, 2023 will mark the centennial of Edwin Hubble's discovery of a Cepheid variable star in M31. Hubble found this variable star, which has since been dubbed M31-V1, on plate H335H taken with the 100-inch Hooker telescope atop Mt. Wilson on the night of October 5/6, 1923. He marked it in red with tick marks and "VAR!", for variable. Cepheid variables are standard candles which can be used to determine distance. Hubble imaged M31-V1 on every successive clear night he could to determine its period and its apparent magnitude. He then used Harlow Shapley's (flawed)calibration of the Period-Luminosity relationship to calculate that M31 lies at a distance of about 900,00 light-years, proving it had to be another galaxy and thus solved the mystery of the spiral nebulae. They are other galaxies. The universe suddenly became unbelievably enormous. In August, 2021 I imaged M31-V1 and measured its nightly magnitude over a period of 57 consecutive nights to make the light curve shown. From the period and apparent magnitude derived, and using the same calibration of the Period-Luminosity relationship that Hubble used, I also got a distance of 900,000 light-years, precisely reproducing Hubble's result. I also calculated the distance using the much more modern calibration of the Period-Luminosity relationship derived from the Hubble Space Telescope and got a distance of 2,531,000 light-years, which is extremely close to the currently accepted distance of 2,537,000 light-years. Happy Centennial to all the galaxies in the universe!
