Light Years
Science: KS3, topic 3.6.9
Light Years
A light year is a distance, not a length of time. Light years were first used by the German astronomer Friederich Bassel in 1831.
Speed of light
- The light we see from Earth comes from the Sun.
- Light takes 8 minutes 20 seconds to travel from the Sun to Earth.
- So the sunset we see happened 8 minutes 20 seconds earlier.
Earth-Sun distance
- The Earth and Sun are 93 million miles apart.
Light and sound speed
- Light travels at 300,000,000 m/s (sound only travels at 340 m/s!).
Light years
- A light year is the distance light travels in 1 year.
- A light year is 9.5 trillion km.
- Our second nearest star is Alpha Centauri.
- Light from Alpha Centauri takes over 4 years to reach us.
Test yourself on Light Years
What do light years measure?
What is the speed of light?
Which of the following are true of light years?
How long does it take light to reach the Earth from the Sun?