The Hubble Space Telescope — Personal Reflections on the 25th Anniversary
April 25, 2015 marks 25 years since the Hubble Space Telescope was released from the Space Shuttle cargo bay to become a free-flying mini-moon of Earth. Since that time, this amazing spacecraft has logged some 5 billion kilometers (3 billion miles) in its orbit around Earth. But if that distance sounds far, it is nothing compared to how much farther Hubble has seen. If Hubble had traveled the 5-billion-kilometer distance straight outward into space, it would now take its light a little more than 4 ½ hours to travel back to Earth. But the light that Hubble has recorded from some distant galaxies has traveled through space for more than 12 billion years to reach us. Hubble has dramatically enhanced our view of the universe, both in space and in time.
Hubble’s story is being retold in many media retrospectives, so I’ll give only the briefest overview here. From the time Galileo first turned his telescope to the sky in 1609 until the launch of Hubble, nearly all astronomical observations had been conducted with telescopes on the ground. (Yes, there were a number of space observatories prior to Hubble, but none that could take visible light pictures with anywhere near the same power.) While these telescopes had taught us much about the universe, astronomers had long recognized that ground-based telescopes suffered from two major limitations:
- Because ground-based telescopes peer through Earth’s turbulent atmosphere, their images tend to be blurred; in essence, it is the same effect that makes stars twinkle in the night sky, even though the stars themselves are steady sources of light.
- Much of the light that comes to us from the cosmos is in forms that our eyes cannot see, such as infrared and ultraviolet light, most of this light cannot penetrate Earth’s atmosphere, rendering it impossible —> Read More