The Speed of Light

Light is the fastest thing in the universe. It travels at about 186,000 miles per second. At that speed, light could go around the Earth about 7.5 times in one second. Nothing can travel faster than light. Even at this incredible speed, light from distant stars takes years to reach us.

How Fast Is Light

Light travels at exactly 299,792,458 meters per second in a vacuum. It takes about 8 minutes for sunlight to reach Earth. Light from the nearest star beyond the Sun takes over 4 years to reach us. Light from distant galaxies has been traveling for billions of years to reach our telescopes.

Light Years

Distances in space are so enormous that scientists use light years to measure them. A light year is the distance light travels in one year, about 5.88 trillion miles. The nearest star to our Sun, Proxima Centauri, is about 4.24 light years away. The Milky Way galaxy is about 100,000 light years across.

Fun Facts

• It takes light about 1.3 seconds to travel from the Moon to Earth.
• If you could travel at the speed of light, time would appear to stop for you.
• The speed of light was first measured accurately in 1676 by studying Jupiter's moons.

Did You Know?

When you look at the stars, you are looking back in time. The light from some stars you see tonight left those stars hundreds or thousands of years ago. You are seeing what those stars looked like long ago!