Listen&Learn: The speed of light

Learn how scientists use the speed of light to measure distances between stars.

Pre-listening vocabulary

• theory: a scientific explanation for something
• vacuum: a completely empty space
• constant: never changing or stopping
• exoplanet: a planet outside of our solar system
• visible: able to be seen

Listening activity

Podcast: Play in new window | Download (Duration: 1:19 — 1.2MB)

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Gapfill exercise

Einstein’s theory of special relativity states that it is for anything to travel faster than light. In a vacuum, light travels at a constant speed of 299,792,458 metres per second. Scientists use the speed of light to distances between stars in space. A light-year is a that represents the distance that light can travel in a year. Even the closest stars and exoplanets are removed from our system by several light-years. Proxima Centauri, the closest star to the Sun, is about 4.25 light-years away. Some visible stars are thousands of light-years away. This means that the night sky is an image of the . In fact, it is possible that some of the stars we can see no longer exist.

Comprehension questions

See answers below

1. Einstein’s theory of special relativity states that
   a. it is impossible for something to travel faster than light
   b. light travels at an accelerating speed
   c. the light from stars reaches Earth almost instantly
   
2. A light-year is a measure of
   a. time
   b. distance
   c. energy
   
3. The closest star to the Sun is about
   a. 4.25 light-years away
   b. 299 light-years away
   c. 1000 light-years away

Discussion/essay questions

1. Einstein’s theory of special relativity also states that speed can change the way we experience time. Do you think time travel will ever be possible? Why or why not?

Transcript

Einstein’s theory of special relativity states that it is impossible for anything to travel faster than light. In a vacuum, light travels at a constant speed of 299,792,458 metres per second. Scientists use the speed of light to measure distances between stars in space. A light-year is a unit that represents the distance that light can travel in a year. Even the closest stars and exoplanets are removed from our solar system by several light-years. Proxima Centauri, the closest star to the Sun, is about 4.25 light-years away. Some visible stars are thousands of light-years away. This means that the night sky is an image of the past. In fact, it is possible that some of the stars we can see no longer exist.

Answers to comprehension questions

1a 2b 3a