A deep space image from the Hubble Space Telescope Most of the objects are distant galaxies. |
Light travels very, very fast (186,000 miles per hour, or 300,000,000 meters
every second!). The Universe is also very, very big. Scientists
have even found that the Universe is expanding. The things
at the very edge of the Universe are so far away that it takes the
light that they emit billions of years to get to Earth. Scientists
think that the Universe is about 12 billion years old. So the light
that is reaching us from the edge of the Universe has traveled a distance
of 12 billion light years, and is 12 billion years old.
(Note that a light year is a measure of distance and not time.)
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Since the Universe is expanding, all the galaxies and stars are
moving away from us. Galaxies at the edge of the Universe are moving so
fast that the light they emit has
changed when we see it. The visible light that they emit looks like
infrared light when it gets to us. Scientists call this phenomena 'redshift'.
Light is redshifted when the source is moving away from the observer, just
like sound changes when its source is moving. Think of how the sound of
a train whistle changes as it speeds past you.
As the train recedes into the distance, the pitch of the whistle is lower.
This is the soundwave analogy of redshift except when the frequency of
light waves is lower, the light appears redder.
Since the light reaching us from the edge of the Universe is redshifted from
visible light to infrared light, we need the Spitzer Space Telescope to see the
infrared light of the very early Universe. In a way, Spitzer can see
back to near the beginning of the Universe. |
 Some of the farthest galaxies we have ever seen, Imaged by the Hubble Space Telescope. |
What is the Spitzer Space Telescope?
What is the Purpose of the Spitzer Space Telescope?
What Will the Spitzer Space Telescope Do?
Building the Spitzer Space Telescope