Looking Back in Time

When Astronomers probe the deepest regions of space they are actually looking back in time. This is simply because of the finite speed of light. Light moves at the speed of 300,000,000 meters/second (186,000 Miles/second). At short distances, like from satellites in orbit of Earth, the light travel time is only a fraction of a second. However, the Sun is so distant from Earth (150,000,000 Kilometers) that its light takes 8 minutes to reach us. So when you look at the sun in the sky (never look at it directly, you'll go blind) you see it as it was 8 minutes ago.

As distances get larger so does this "look-back time." Our closest stellar neighbor, Alpha Centauri, is so far away that its light travels for 4.3 years before reaching us. When we look at the closest spiral galaxy to our own Milky Way, the Andromeda galaxy, we see it as it was 2 million years ago (when Homo Sapiens first began walking the Earth).

The Hubble Space Telescope has taken a picture called the Hubble Deep Field (pictured here). When we gaze at those ancient galaxies we are seeing a distant part of the universe as it was billions of years ago (when Earth was still in its infancy).

Last modified May 6, 2008 by Randy Russell.

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