We continue ‘Discovering Mount Wilson’ with Chapter six and the discovery of the Milky Way’s true size and shape. From Earth, the Milky Way appears as a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. Most astronomers at work from 1914-1918 thought that the Milky Way was the entire universe and that our Sun was near the center of the Milky Way Galaxy.
Harlow Shapley – Source UnknownHarlow Shapley came to Mount Wilson in 1914 after receiving his PhD from Princeton University. During his time there, he studied globular clusters and published several papers revealing for the first time the size and structure of our Milky Way Galaxy. For centuries everyone could see the Milky Way but no one knew what they were looking at in the night sky.
By using the light gathering power of the 60-inch telescope, Shapley was able to provide evidence by 1918 that our solar system is instead half- way out toward the edge of our Galaxy. It was by using the Cepheid period-luminosity relationship discovered by Henrietta Swan Leavitt (1908-1912), and calibrated by Ejnar Hertzsprung (1913), that astronomers (including Shapley) could begin to measure distances up to 20 million light years. As a result, we now know that our own galaxy, the Milky Way, has a diameter of about 100,000 light years.
Astronomers currently calculate that the Milky Way is one of billions of galaxies in the universe, and is – itself –home to 250-300 billion stars, including the one most significant to human beings residing in an outer arm of the galaxy – our very own Sun.
