The Speed of Light as a Limit

Lab Brief #6

🎯 Your mission

Master the concept. Use it tomorrow.

⚡ The twist

The light you see now started its trip a long time ago.

What you'll learn

Light travels at 3 × 10⁸ m/s in a vacuum, and nothing carrying information can exceed it. That finite speed means looking further away is looking further back in time: the Sun you see is eight minutes old, and distant galaxies appear as they were billions of years ago.

Key words

light-year
The distance light travels in one year, about 9.5 × 10¹² km.
lookback time
The time light has taken to reach us, so distant objects are seen as they once were.

Make a hypothesis first

Guess: how big does that look from here vs. from there?

Say your guess out loud — then find out if you were right.

Step 1 of 4 · Read

Think about what you just learned: say what "light-year" and "lookback time" mean in your own words before you start.

Step 2 of 4 · Do

Calculate the light travel time from the Moon, the Sun, Proxima Centauri and the Andromeda galaxy. Present them on a single timeline showing what era of Earth history each image left during.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

Light from the Sun takes about how long to reach Earth?

How sure are you?😐 maybe

Question 2 of 2

A light-year is a unit of:

How sure are you?😐 maybe

Mind = blown

🌌 If you could drive a car straight up at highway speed, you'd reach space in under an hour.

Nice work!

You got 0 of 2 right.

All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: GPS, weather forecasts, and the seasons all rely on this.

🏆 Stretch challenge (try it this week): Find a constellation in the sky. Look it up. Tell someone its story.

👨‍👩‍👧 For the dinner table: “If you could visit any planet, which would you pick and why?”

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