You don't need a time machine to see the past -- just your eyes and a clear sky full of stars. As darkness falls tonight, for example, look high in the sky for yellow-orange Arcturus. It's 37 light-years away, which means we see it as it looked 37 years ago. And low in the southeast, you can see even farther into the past -- about 600 years, to the orange star Antares.
But if you'd been looking at just the right spot on the night of March 19th, you could have gazed back to a time before the birth of our planet.
On that night, an orbiting telescope detected the most powerful explosion ever measured. For a little while, it was bright enough to see with the unaided eye. Telescopes on the ground, including the Hobby-Eberly Telescope at McDonald Observatory, measured its distance at 7.5 billion light-years. That means the explosion took place about three billion years before the birth of the solar system. That made it by far the most-distant object visible to the unaided eye ever recorded.
The explosion was a gamma-ray burst. It probably marked the destruction of a massive star. The star's core may have collapsed to form a black hole, while its outer layers were blasted to bits. "Jets" of gamma rays may have been beamed from the poles of the star, with one of the jets aiming at Earth.
The blast faded quickly. But for a while, it offered a glimpse at the distant past -- a time capsule from seven and a half billion years ago.
Script by Damond Benningfield, Copyright 2008
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