Mon Prof Augmenté
Looking Back in Time
Age 12 · Astronomy
Light needs time to travel across space, so the light from a faraway galaxy left it long ago. The farther away something is, the older the light we see, so telescopes show us the past.
This picture is part of the full library
Every lesson is open to everyone for 7 days after it is published. This one came out on October 25, 2026: its text stays readable here, and its picture opens with a subscription.
The app is free. A subscription opens every lesson, in every school year.
In the picture
- Telescope on Earth: catches light that is only arriving today
- Nearby galaxy: its light left about 2.5 million years ago, when early human ancestors walked the Earth
- Distant galaxy: its light set out about 100 million years ago, when dinosaurs lived
- Faint glowing haze: the oldest light, from when the young universe was a hot, glowing fog
Examples
- When you look at the Sun, you see it as it was about 8 minutes ago, because that is how long its light takes to reach us.
- Thunder reaches you after the lightning flash because sound travels more slowly, just as distant light arrives late.
Key takeaways
- Light is very fast, but it still takes time to cross the huge distances of space.
- The farther away we look, the further back in time we see.
Quiz: Looking Back in Time (Age 12)
-
Why does looking at a faraway galaxy show us the past?
-
Two galaxies can be seen through a telescope: one is close, the other is much farther away. Which one sends us older light?
-
Light arriving today from a nearby galaxy left it about 2.5 million years ago. What does a telescope show us?
The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.
Free app, optional subscription
App Store Google Play
Carry on in the app
At least one new illustrated lesson every weekday for your child’s year, with its quiz and a reminder at 6:15 pm.
Your child’s teacher does not use My Enhanced Teacher yet?
Tell them about it
