Astronomy Picture of the Day

Explanation: No person in history has had greater impact in determining the extent of our universe than Edwin Hubble. From proving that other galaxies existed to proving that galaxies move apart from one another, Hubble's work defined our place in the cosmos. Hubble lived from 1889 to 1953 and is shown above posing with the 48-inch telescope on Palomar Mountain and his famous pipe. In memory of his great work, the Orbiting Space Telescope was named after him. The rate of the universe's expansion is now parameterized by a quantity known as Hubble's constant. A modern debate on the value of Hubble's constant took place in 1996.