How is it that we see farther out in space (farther back in time) than in the past? (Beginner)

Many a times we read about how telescopes and probes look back in time. We seem to be able to look back further as we move farther from the earth. For example the recent "probe" which took a "picture" of the universe at age 380,000 years after the big bang.

Now I understand that the light or radiation that we observe started out light years before we observed it and therefore we are acutally seeing back in time when we observe this. But how do these observations go further back in time as we move away from the earth ? This could only be possible if were travelling at faster than light speed and therefore have the ability to move a few light years back from the earth and look at light which left its origin even earlier.

It's not the case that space-based telescopes can see farther away (farther back in time) because they're far away from the Earth. At least, that's not the direct reason.

The reason why we can get impressive pictures of the very distant universe now that we couldn't get 20 years ago is because the technology is better. So we can build better telescopes that are more sensitive. The proximity of a space-based telescope to the Earth is only an issue in the sense that the Earth is a big source of light pollution across a broad region of the spectrum. So a telescope that's far away from the Earth doesn't have to worry about interference from the Earth.

For example, Spitzer (formerly the Space Infrared Telescope Facility (SIRTF)), an infrared telescope that was launched in August 2003, is in an orbit that puts it 15 million kilometers away from the Earth. The idea is to keep it away from the visible and infrared light of the Earth. If it was closer to the Earth, then it wouldn't be as sensitive. So in that sense, you're right that there's a link between how far you are from the Earth and how far away you can see, but it's not quite the kind of link that you describe.

This page was last updated June 27, 2015.

About the Author

Christopher Springob

Christopher Springob

Chris studies the large scale structure of the universe using the peculiar velocities of galaxies.  He got his PhD from Cornell in 2005, and is now a Research Assistant Professor at the University of Western Australia.

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