Happy Birthday Hubble

Atlantis (right) on Pad 39-A and Endeavour (left) on 39-B. The latter pad has lightning towers installed in anticipation of the Ares 1-X test.

On April 24, 1990 the Hubble Space Telescope was launched aboard Space Shuttle Discovery. The dream of an observatory in Space was achieved after many delays, including Challenger's accident in 1986. Hubble was the first free-flying Space observatory designed to be serviced by astronauts. Having humans in space was very fortunate when Hubble was found to have a spherical aberration. STS-125, the fourth Hubble servicing mission, is scheduled to launch May 11 onboard Atlantis. (This week the date was moved forward from May 12.) Endeavour will be sitting on Pad 39-B in case of rescue.

Albert Einstein thought that the Universe was spherical, but of a fixed radius. Einstein's equations showed that the static Universe would be unstable, UNLESS it were expanding. If Einstein had foreseen an expanding Universe, it would have been one of history's great scientific predictions. Instead he added a repulsive energy, a "cosmological constant."

By comparing the luminosity of Cepheid Variables with the host galaxies' redshifts, Edwin Hubble discovered that the Universe was expanding. After visiting Hubble atop Mount Wilson, Einstein withdrew his cosmological constant. Later Einstein would call the CC his greatest blunder.

Edwin Hubble's rough graphs showed the galaxies recede in proportion to their distance, indicating expansion. This ratio is called the "Hubble Constant" though everyone knows that it would change with time. Finding the precise value of the Hubble "constant" was a key science mission of HST. When physicists used HST to look at distant supernovae, they found that expansion appeared to accelerate with respect to the speed of light. If they had announced that the speed of light was slowing it would have been one of history's great discoveries. Instead physicists concluded that a cosmological constant or "dark energy" was causing acceleration.

Once even Einstein thought that the Universe was static. Observations by Edwin Hubble, Milton Humason, and others showed that its size changed. Once upon a time physicists thought that the speed of light was also static. As with Hubble's constant, observations show that even constants can change.

1-minute video: 10,000 galaxies seen by the Hubble Ultra Deep Field