Distances in Space | The Schools' Observatory

Distances to objects in space are very, very large. The nearest star (excluding the Sun), Alpha Centauri, is 41.23 trillion km, or 41,320,000,000,000 km!!

Therefore, astronomers use a unit called a light-year, which is the distance that light can travel in a year. Knowing the speed of light, we can calculate the distance of a light-year.

In this activity, you will use the speed/distance/time equation to calculate the length of a light-year in metres, then use this information to calculate how far away Alpha Centauri is in metres!

By the end of this resource you will:

Have used the speed/distance/time equation
Have rearranged an equation
Know that the speed of light is a constant
Have used the speed of light to determine astronomical distances

To complete this resource you will need:

To read the instructions on this page
The worksheet below
A calculator

Files or Documents

Distances in Space Worksheet

Distances in Space Worksheet Answers

A space image, with stars on one slide and a galaxy on the other, there is a cartoon tape measure being pulled between them.

Approx Duration

15 - 30 mins

Have a go!

Before you start:

Download the Distances in Space worksheet.

Follow the instructions in the worksheet to complete the questions

Remember to convert all of the numbers into the same unit for each equation!

Now follow the instructions on the worksheet:

Use the equation triangle to work out how to calculate the distance.
Use the equation on the sheet to calculate the number of seconds in a year (don’t forget leap years!)
Use the speed of light and the time you have just calculated to work out the distance of one light-year in metres.
Now convert the distance to Alpha Centauri into light years from metres.

You can check your answers using the answer sheet at the top of this page.

You may find that this number varies slightly from others found online. Remember that we have used an approximation of the speed of light.

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