Rocket wants to design a ship to visit the nearest star. He starts with a ruler.
"First, how far is the Sun?" he asks.
Raven reads from her wrist computer. "About 93 million miles," she says. "And the next nearest star is much, much farther."
Rocket puts the ruler down slowly. "I am going to need a bigger ruler."
Nova laughs. "Astronomers have one," she says. "Would you like a hint? It is measured with light."
The Sun is about 93 million miles from Earth.
Light from the Sun takes about eight minutes to travel that far and reach Earth.
For stars, miles get too big to use. So astronomers use light-years.
A light-year is how far light can travel in one year. That is about 5.88 trillion miles.
After the Sun, the nearest star is Proxima Centauri. It is about 4.24 light-years away.
Light from the Sun reaches us in about eight minutes. Light from Proxima Centauri takes more than four years.
| Star | Distance from Earth | Time for its light to reach us |
|---|---|---|
| The Sun | About 93 million miles | About 8 minutes |
| Proxima Centauri | About 4.24 light-years | About 4.24 years |
Space is so big that miles are not a handy ruler.
So astronomers measure with light. Light travels very fast.
Even so, light from the nearest star after the Sun takes more than four years to reach us.
| Statement | True or false? |
|---|---|
| A light-year measures distance. | ? |
| Proxima Centauri is about 4.24 light-years away. | ? |
| Light from the Sun takes about eight years to reach Earth. | ? |
| A light-year is about 5.88 trillion miles. | ? |
Huge numbers, handled like a scientist. Tomorrow you will use the Sun to make a shadow clock.