Practice using light years to describe distance, compare space scales, and understand how long light takes to travel across the universe.
Read each problem carefully. Show your work in the space provided. Use complete sentences when explaining your thinking.
Understanding how astronomers measure enormous distances
Astronomy - Grade 6-8
- 1
A light year is the distance light travels in one year. Explain why a light year measures distance, not time.
- 2
Light from the Sun takes about 8 minutes to reach Earth. Is the Sun 8 light minutes away or 8 light years away from Earth? Explain your answer.
- 3
Proxima Centauri is about 4.2 light years from Earth. How long does light from Proxima Centauri take to reach Earth?
- 4
Sirius is about 8.6 light years from Earth. If you see Sirius tonight, how old is the light that reaches your eyes?
- 5
One light year is about 9.5 trillion kilometers. Estimate the distance to a star that is 3 light years away in kilometers.
- 6
The Milky Way galaxy is about 100,000 light years across. Explain what this means about light traveling from one side of the galaxy to the other.
- 7
Put these distances in order from smallest to largest: 8 light minutes, 4.2 light years, 100,000 light years, 1 light second.
- 8
A spacecraft travels much slower than light. Explain why even nearby stars are very difficult for spacecraft to reach.
- 9
If a galaxy is 2 million light years away, what does it mean when we look at that galaxy through a telescope?
- 10
Two stars are at different distances from Earth. Star A is 10 light years away, and Star B is 25 light years away. Which star's light has traveled longer to reach Earth, and by how many years?
- 11
A scale model uses 1 centimeter to represent 1 light year. In this model, how far from Earth would you place a star that is 12 light years away?
- 12
Explain why kilometers are useful for measuring distances on Earth, but light years are more useful for measuring distances between stars.