Hubble proposed a system to describe galaxies by their shape. His system still is used today. He also showed that galaxies are similar in the kinds of bright objects they contain. All galaxies, he said, are related to each other, much as members of a family are related to each other.
In the late nineteen twenties, Hubble studied the movement of galaxies through space. His investigation led to the most important astronomical discovery of the Twentieth century -- the expanding universe.
Earlier observations about the movement of galaxies had been done by V. M. Silpher. He discovered that galaxies are moving away from Earth at speeds between three hundred kilometers a second and one thousand eight hundred kilometers a second.
Hubble understood the importance of Silpher's findings. He developed a plan for measuring both the distance and speed of as many galaxies as possible. With his assistant at Mount Wilson, Milton Humason, Hubble measured the movement of galaxies. The two men did this by studying what Hubble called the "red shift." It also is known as the "Doppler effect."
The Doppler effect explains changes in the length of light waves or sound waves as they move toward you or away from you. Light waves from an object speeding away from you will stretch into longer wavelengths. They appear red. Light waves from an object speeding toward you will have shorter wavelengths. They appear blue.
Observations of forty-six galaxies showed Hubble that the galaxies were traveling away from Earth. The observations also showed that the speed was linked directly to the galaxies' distance from Earth. Hubble discovered that the farther away a galaxy is, the greater its speed. This scientific rule is called "Hubble's Law."
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2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25