Coffee & Cosmos: What’s a Light-Year Anyway?

A light-year is a way to measure distance in space. It is the distance light travels in one year, which is about 9.46 trillion kilometers.

If a star is 10 light-years away from Earth, what does that mean?

It means it takes 10 years for the light from that star to reach our eyes.

When we look at a star that is 50 light-years away, we are seeing the star as it looked 50 years ago.

FACTS:

It takes about 8 minutes for light to travel from the Sun to Earth.
Proxima Centauri is the closest star to Earth. It is 4.24 light-years away!

The distance across the Milky Way galaxy is about 100,000 light-years.

Scientists use light-years because miles and kilometers are too small to measure the huge distances in space.

The distance across the solar system is about 1 to 1.5 light-years.

3

Light-years

Good Luck!

1 / 7

What does a light-year measure?

Time

Speed

Distance

Brightness

2 / 7

Approximately how far does light travel in one year?

300,000 kilometers

9.46 million kilometers

9.46 billion kilometers

9.46 trillion kilometers

3 / 7

Why do astronomers use light-years to measure distances in space instead of units like miles or kilometers?

Miles and kilometers are too small to be practical for the vastness of space.

Light-years are a unit of time, which is more relevant to astronomy.

It is impossible to calculate distance in space using standard metric units.

Using light-years helps scientists measure the speed of light more accurately.

4 / 7

Which of the following distances is the greatest?

The distance across our solar system

1 light-year

The distance to the nearest star (Proxima Centauri)

The distance across the Milky Way galaxy

5 / 7

Approximately how long does it take light to travel from the Sun to Earth?

1 second

1 minute

1 hour

8 minutes

6 / 7

When we look at a star that is 50 light-years away, we are seeing the star as it was:

as it is right now.

50 years ago.

50 years in the future.

100 years ago.

7 / 7

If a star is 10 light-years away from Earth, what does that mean?

The star will reach Earth in 10 years.

It takes 10 years for light from that star to reach our eyes.

The star is moving away from Earth at 10 times the speed of light.

The star is 10 years old.

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