Rotating Question Curious About Astronomy? Ask an Astronomer

How long does it take for the Sun's light to reach us?

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.

January 1999, Laura Spitler (more by Laura Spitler) (Like this Answer), Dave Kornreich (more by Dave Kornreich) (Like this Answer)

Still Curious?

Get More 'Curious?' with Our New PODCAST:

Related questions:

More questions about The Sun: Previous | Next

How to ask a question:

If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.

Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist

This page has been accessed 369419 times since September 6, 2002.
Last modified: June 18, 2010 10:01:47 AM

Legal questions? See our copyright, disclaimer and privacy policy.
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.

Warning: Your browser is misbehaving! This page might look ugly. (Details)