By: Patricia Hageman
September 7, 2011
When I think of an accomplished Astronomer from the 20th century, the first person to come to mind is Edwin Powell Hubble. He had numerous achievements in the study of Astronomy before his death in 1953. Among those was his discovery of galaxies outside of the Milky Way, the expanding universe, and overseeing the construction of the Hale Telescope. Because of his major contributions to the study of Astronomy, the Hubble Space Telescope was named after him in 1990.
One of Hubble’s first discoveries was that there are other Galaxies outside of our Galaxy, the Milky Way. In the 1920s, the small, diffuse patches in the sky were termed nebulae, and were thought to exist within the Milky Way. While examining images of the galaxies, NGC 6822, M33, and M31, Hubble noticed a pulsating star known as a Cepheid variable inside each one. Cepheids are special because their pulsation allows for precise measurements of distance. Hubble calculated how far away each Cepheid lay — and thus how far to each nebula — and realized they were too distant to be inside of the Milky Way. Astronomers realized that these nebulae were in fact galaxies like the Milky Way, each containing billions of stars. The universe, once thought to be contained by the Milky Way, expanded significantly in the eyes of astronomers (Space.com, 2012). This was an amazing discovery in Astronomy and led to Hubble publishing a classification system for these galaxies. Hubble published a standard classification system to use for the galaxies. At the time, a descriptive system existed, and two other systems were proposed soon after, but they were insufficient (Space.com, 2012).Hubble’s classification system had galaxies sorted by content, distance, shape, and brightness. Hubble's clear method of organizing the various classes focuses on three galactic types: ellipticals, spiral and barred spirals, and irregulars. Known...