Astronomer Edwin Hubble formally announced that the Milky Way is just one of many galaxies in the universe

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Humans thought the earth was the center of the creation or universe before Copernicus and Galileo. After, they found that the sun and planets did not revolve around the Earth. Also, they discovered the sun was the center of our solar system but was not the center of the universe. However, humans still thought our Milky Way contained all or most of the stars in existence, and the sun was a major star in our galaxy.

After, astronomer Edwin Hubble found several stars in Andromeda. Also, he discovered Cepheid variable stars. Here, the brightness of the star and its period, and the length of time it takes to go from bright to dim and back again were used to determine how far away it is. Using Henrietta Leavitt's formula, Hubble determined that Andromeda was roughly 860,000 light years away. It is more than eight times further than the most distant stars in the Milky Way. According to that, he proved that the nebulae are separate star systems from the Milky Way and that the universe is not only our galaxy using Mount Wilson Observatory’s new 100-inch Hooker Telescope. 

Hubble added another astronomical accomplishment to his reputation before the 1920s ended. He proved that their redshift was proportional to their distance by examining the Doppler impact on the spectroscopic signals of the stars. Also, He showed the universe is expanding by discovering another couple of dozen galaxies. This idea led to the big-bang theory.

On December 30th, 1924, Hubble formally announced that the Milky Way is just one of many galaxies in the universe and that there are other galactic systems at the meeting of the American Astronomical Society. In January 1949, when the 200-inch Mount Palomar telescope was completed, Hubble was the first astronomer to use it. NASA honored his achievements by naming its space telescope after him.