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My questions are. How long does it take for the light from the sun to reach the Earth, and other planets in the Milky Way? How far does the sun's light travel beyond our solar system? How much larger is the sun compared to the planets in our solar system? Thank you for your time.

The sun's light takes about 8 minutes to reach the Earth after it has been emitted from the sun's surface. The time it takes for light to reach planets in our Solar System (not the Milky Way, which is our galaxy) varies from about 3 minutes for Mercury, to about 5.3 hours for Pluto. There is nothing out in space to prevent the sun's light from going infinitely far, in principle. In practice, the sun is only 4.5 billion years old, so its light can only extend 4.5 billion light years away from us right now. But there's nothing to stop that light from expanding outwards forever, as time goes on. The sun's radius is about 100 times that of the Earth, meaning that about 1.12 million Earths could fit inside it, as could about 930 Jupiter's.

If it takes just over 8 minutes for the Sun's light to reach Earth, then if the sun were to suddenly extinguish, would we not know it until just over 8 minutes later?

This is correct. There's no reason for the Sun to suddenly turn off, but more generally, the light from flares or other stellar "weather" also takes 8 minutes to reach us.

This page was last updated June 28, 2015.

About the Author

Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.

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