On Oct. 6th, 1923, Edwin Hubble took one of the most important images in the history of astronomy. The image, featured as today's Astronomy Picture of the Day, is of what was then known as the Andromeda spiral nebula, which we now know today as the Andromeda Galaxy.
Hubble discovered a cepheid variable star in the Andromeda nebula [galaxy], a star that changes its brightness at precise time intervals based on its size and temperature. This information provided Hubble with the necessary information to calculate the distance for this object. To Hubble's amazement, the star was located millions of light years away, far outside the known distances of previously recorded objects.
Before this discovery, the universe was thought to consist of a flat disk of stars and nebulae, including spiral nebulae, that were all part of our Milky Way Galaxy. What was not understood was that these spiral nebulae were galaxies in their own right, each consisting of hundreds of billions of stars!
Follow-up observations of other galaxies later helped to determine that not only were these galaxies at great distances but spectral analysis was seen to display what is known as "redshift". Redshift is a shift in the light spectrum of an object due to the Doppler effect. The redshift of these galaxies showed that the further a galaxy was, the faster it appeared to be moving away from us. These results helped to support the theory which is now known as the "Big Bang".
Just as theorized by Copernicus and proven through multiple observations by Galileo that the Earth was not the center of the solar system, Hubble's model once again shifted our galaxy from its central position to one galaxy of the hundreds of billions of galaxies in our known universe. This concept, less than 100 years old, is now common knowledge of elementary-age students and has fueled the interest in astronomy by the general public.
What discoveries will we make in the years to come that will once again shift our understanding of our cosmos? Will it be additional dimensions? The discovery of life beyond Earth?
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