When you look at the stars, you travel through time!

Light is a Super Fast Rocket!

Did you know that light is the fastest thing in the entire universe? It travels at an incredible speed of 300,000 kilometers per second. It's so fast that it could go around the Earth 7 times in just one second!

Why Does Seeing the Stars Mean Traveling Through Time?

The stars are so far away from us that their light takes a long time to reach us. When you look at a star in the sky, you don't see it as it is now, but as it was at the moment its light began its journey toward Earth.

Our Eyes Are Time Machines

Every night, you can take little trips through time just by looking at the sky:

• The Moon: you see it as it was 1.3 seconds ago.
• The Sun: you see it as it was 8 minutes ago.
• Sirius (the brightest star): you see it as it was 8.6 years ago.
• Betelgeuse (in Orion): you see it as it was 640 years ago.
• The Andromeda Galaxy: you see it as it was 2.5 million years ago, long before modern humans appeared.

Telescopes Are Also Time Machines

Astronomers use very powerful telescopes like Hubble (Hubble Space Telescope) or James Webb (James Webb Space Telescope) to look ever farther into the universe. And the farther we look, the further into the past we see! Some galaxies we observe today may not even exist anymore.

A Light from the Age of the Dinosaurs

When you observe certain very distant stars, their light began its journey toward Earth at the time when dinosaurs walked on our planet. This light traveled for millions of years through space to finally arrive in your eyes tonight!

How Does It Work? The Speed of Light

The speed of light is represented by the letter c. It's a symbol used by scientists to talk about this incredible speed. Nothing can go faster than light. We simply write this: \(v <c\).

N.B.:

A light-year is a unit of distance, not of time! It's the distance light travels in one year, about 9,460 billion kilometers. For example, if a star is 100 light-years away, that means its light takes 100 years to reach us.