Why does light take time to reach us from distant stars?
Quick Answer
Because light travels at a finite speed, about 299,792 kilometers per second, so looking far away means looking into the past.
The Full Story
Light does not travel instantaneously; in a vacuum it moves at about 299,792 kilometers per second. That means light from the Moon takes about 1.3 seconds to reach Earth, sunlight takes about 8 minutes, and light from many stars can take years or even thousands of years. When astronomers observe a distant galaxy, they are seeing it as it was long ago. This is why telescopes are sometimes described as time machines. The farther out we look, the deeper we see into cosmic history.
Key Facts
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Suggested video title for this topic:
"Look at a star, and you’re literally looking back in time."
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