How old do I look?

How old do I look?


You will find out when you play "What's Older?"



Signs of aging




Cosmic time stamp


No matter what, light always travels at the same speed in space.



The Galaxy Evolution Explorer Looked Back in Time

Artist's rendering of GALEX

Artwork of Galaxy Evolution Explorer in orbit above Earth.

The Galaxy Evolution Explorer is a space telescope that was launched into orbit around Earth in 2003. Its mission is now complete. It has mapped thousands of galaxies over a large part of the sky, looking back into cosmic time to see what the universe was like 10 billion years ago.

This amazing explorer saw ultraviolet light, a kind of light not visible to humans. To see ultraviolet light, the telescope had to be in space, because very little of this kind of light can shine through Earth's atmosphere. Galaxy Evolution Explorer was particularly good at seeing areas of galaxies where stars are forming, because young stars glow more brightly in ultraviolet light than do older stars.

Galaxy Evolution Explorer saw starlight that had been traveling for just a few years from stars that are "only" a few trillion kilometers away. But it also saw really old, red-shifted starlight. Light from the farthest of these had been traveling for most of the 13.7 billion years that the universe has existed! So Galaxy Evolution Explorer saw galaxies as they were billions of years ago, as well as how the nearby galaxies looked just a few hundred thousand years ago.

GALEX image of spiral galaxy M81



Just as you look younger in a picture of you from several years ago, Galaxy Evolution Explorer observed galaxies as they looked when they were much younger, because that is when the light reaching the ultraviolet telescope was emitted. By comparing these "far" pictures with the "near" pictures, astronomers can see how galaxies and their stars are born, age, and die over time. They can learn how galaxies evolve.

Look at more pictures from Galaxy Evolution Explorer, and see how they are different from pictures taken by ordinary, visible light telescopes.

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