November 20, 2010

Happy Birthday, Edwin Hubble

Born on this day in 1889 in Missouri, Hubble's family soon moved with him to Illinois. This early move perhaps presaged a varied and movement-filled life.

As a high school student, Hubble was into sports, especially track and field, and he set his state's high-jump record in 1906. In college he studied philosophy and science, and he got a Bachelor of Science degree, but then he went to Oxford University in England to study law and to get a master's degree in Spanish!

Hubble taught Spanish, physics, and math in a high school in Indiana, coached basketball, and passed the Kentucky bar (which would have allowed him to practice law in that state). Instead he entered the U. S. Army during World War I.

Home from the war, Hubble enrolled in a doctorate program in astronomy, and in 1917 he earned his PhD in that subject. Today we know Hubble from his career in astronomy. Still, that career focused on movement.

Hubble's biggest contribution was the demonstration that there were galaxies other than our own Milky Way, and that these galaxies are shooting away from each other at tremendous speeds. In other words, Hubble showed that the universe is huger than most had ever imagined, and that it was expanding.

Most people today are familiar with the name Hubble because of the space telescope that was named after him.

Extra-galactic Astronomy

One reason I am excited about Hubble is that he did some of his most important work pretty much where I grew up, at the Mount Wilson Observatory, which is very near my childhood home of Pasadena, California.

The other reason I am excited about Hubble is that he pretty much created an entire science—the study of stuff outside of our galaxy. (“Outside of our galaxy” is what extra-galactic means.)

There is a type of variable star whose behavior is very predictable, and we can deduce the distance of these stars simply by measuring their apparent brightness. (Obviously, if two stars were exactly the same size and temperature, the closer star would appear to be brighter.) In 1923 Hubble identified two of these Cepheid variable stars whose distances proved that they lay far outside our galaxy. They were part of what were then known as spiral nebulae. Hubble showed that these spiral features were not spiral-shaped clouds of gas and dust inside our Milky Way Galaxy, but were instead large, far-away spiral-shaped galaxies made up of billions of stars.

Hubble eagerly collected data from other Cepheid variable stars and discovered that, the farther away they were from our galaxy, the faster they and the galaxies they are a part of seemed to be moving away. This relationship, called Hubble's Law, can be explained by the idea of an expanding universe with a beginning known as the Big Bang.

For information on how we know the speed at which galaxies and other astronomical bodies are moving, check out this earlier post

Some links...

Here are some demonstrations that speak to some aspects of modern astronomy, including the concept of the expanding universe. 

And here is a T-shirt about the expanding universe. 

Here is a NASA site with a short talk about the expanding universe.

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