When we look at distant stars, we are looking back in time. What is a light year, how is it measured and why do we measure distance in terms of time?
- Light travels through space at 300 million meters per second.
- A light year is the distance that light travels in one year.
- Although light travels very quickly, distances in space are vast.
- Light from the Sun takes 8.3 minutes to reach Earth.
Nothing can travel faster than the speed of light.
It moves through space at 300 million meters per second.Light travels 300,000,000 meters per second
About the distance from the Earth to the Moon
Astronomers use light years to measure the enormous distances in space.
Using meters, or even kilometers, just isn't practical.
In one year, light travels:
Although light travels very quickly, distances in space are vast.
It takes 8.3 minutes for light to travel from the Sun to the Earth.
This means we don't see things as they happen - a sudden change in the Sun's brightness would take 8.3 minutes to be visible on Earth.
Our nearest star after the Sun is Proxima Centauri, which is 4.2 light years away.
4.2 light years from Earth
When we see it at night, the light we see actually left the star 4.2 years ago.
Despite the speed of light, the vast scale of our Solar System means that when we look into space, we are actually looking back in time.