Monday
Monday: How Far Is Far?
Rocket stands at the Sky Deck corner with a ball under his arm. "If this is the Sun, where do I put Earth?"
"Guess first," Raven says. Rocket takes three big steps and sets down a pebble. "There."
"And Neptune?" Rocket walks to the far fence, about ten steps, and sets down another pebble. "There. Way out."
Raven checks the NASA fact sheet. "What do you notice? Neptune is about thirty times farther than Earth."
Rocket looks at his pebbles. "Thirty times three steps is ninety steps. That is past the fence. Past the street!"
Nova hovers over the Earth pebble. "Your Sun ball is fine," she says. "Your steps are the problem. Pick a better scale."
Distances too big to picture
For six weeks you have modeled the Sun, Earth and the Moon with a lamp and a ball. This week you ask how far apart they really are.
NASA says the Sun is about 150 million kilometers from Earth. That number is too big to picture, so astronomers gave it a name.
The average Earth to Sun distance is called one astronomical unit, or one AU. NASA says this unit gives an easy way to compare the planets' distances.
OpenStax Astronomy adds a comparison. The Sun is about 400 times as far from us as the Moon.
Why a scale matters
A scale is a rule for shrinking distances so a model fits where you are. Every distance shrinks by the same rule.
Rocket's mistake was using three steps for Earth. With Neptune about 30 times farther, his model needed 90 steps.
With one step for Earth, Neptune needs about 30 steps. That fits a yard or a long hallway.
The Next Generation Science Standards say that phenomena too large to see can be studied with models at various scales. This week you build one.
| Distance | In kilometers | In astronomical units |
|---|---|---|
| Earth to the Moon | about 384,000 | a small fraction of one |
| Earth to the Sun | about 150 million | 1 |
| Sun to Neptune | about 4515 million | about 30 |
- Read the question.
- Tap your answer.
| Statement | True or false? |
|---|---|
| One AU is about 150 million kilometers. | ? |
| A scale shrinks every distance by the same rule. | ? |
| Neptune is about three times farther from the Sun than Earth. | ? |
| The Moon is farther from Earth than the Sun is. | ? |
Did you run out of room? Write where you would need to walk to fit all 30 steps.
The facts this week come from the NASA Planetary Fact Sheet at nssdc.gsfc.nasa.gov, NASA at science.nasa.gov and OpenStax Astronomy at openstax.org.
Write whether 30 steps would fit, and what you could use instead of a step if not.
Good start. Tomorrow you meet the fastest traveler there is, and find out that sunlight is always old news.