The discovery of other galaxies!

 It was on December 30, 1924 when astronomer Edwin Hubble announced the discovery of other galaxies. At the time, it was thought that our Milky Way galaxy represented the entirety of the universe. Hubble was studying the Andromeda Nebula using the 100-inch Hooker Telescope at Mount Wilson observatory in California. With a weaker telescope, nebulae just looked like clouds of glowing gas, but with the Hooker telescope — the most powerful telescope in the world at that time — Hubble was able to distinguish individual stars within the nebula. One of the stars in the Andromeda Nebula turned out to be a Cepheid variable: a particular type of star that pulsates and is very bright. Astronomers had figured out a decade earlier that, by observing a Cepheid variable and measuring its brightness and the length of time it takes to go from bright to dim and back again, they could calculate the star's distance from the Earth. Hubble crunched the numbers and realized that the star he was observing was 800,000 light-years away, more than eight times the distance of the farthest star in the Milky Way. It was then that he realized that the "cloud of gas" he'd been observing was really another vast galaxy that was very far away. He renamed the Andromeda Nebula the "Andromeda Galaxy," and went on to discover 23 more separate galaxies. His findings proved that, unimaginably vast though it seemed to us, our Milky Way was just one of many little islands of stars.

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Edwin Hubble

This is the birthday of astronomer Edwin Powell Hubble, born in Marshfield, Missouri (1889). He was a gifted athlete, and for a while, it looked as if he might make a name for himself that way. He ran track and played baseball, football, and basketball. And — with the exception of spelling — he was a bright student as well. At his high school graduation in 1906, the principal said, “Edwin Hubble, I have watched you for four years and I have never seen you study for 10 minutes.” He paused, and then said, “Here is a scholarship for the University of Chicago.” In 1907, he led his college basketball team to their first conference title. Three years later, he earned his degree in mathematics and astronomy.

He was one of Oxford University’s first Rhodes Scholars, but he didn’t study astronomy there — he studied law, to please his father. He came home in 1913 and passed the bar, but his heart wasn’t in the law practice and he quit after a year. He taught high school Spanish, math, and physics, and coached the basketball team, and the students loved him. But when the term ended, Hubble went back to school himself: this time to earn his Ph.D. in astronomy at Chicago University.

After World War I, Hubble joined the staff of the Mount Wilson Observatory, where he studied nebulae. During his work, he discovered that the Andromeda Nebula was actually another galaxy, far away from our own Milky Way, which scientists had long believed was the only galaxy in the universe. He discovered 22 more galaxies, and he also proved that the universe was actually expanding, which supported the Big Bang theory of the origin of the universe. Stephen Hawking called Hubble’s discovery “one of the great intellectual revolutions of the 20th century.”

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