Scale of the Solar System
Use scale models, diagrams, or calculations to represent the relative sizes and distances of objects in the solar system, understanding that the distances between planets are enormously larger than the planets themselves
What a learner can do afterwards
- Explain that if the Sun were the size of a beach ball, Earth would be a pea about 26 metres away
- State that the distances between planets are much greater than the sizes of the planets themselves
- Create or interpret a scale model showing both relative sizes and distances
1 · Read
You know space is huge, and you know the eight planets circle the Sun. But if you tried to draw the whole solar system on one page with the planets at the right size, the distances between them would not fit at all. A scale model fixes this: it shrinks every size and every distance by the same amount, so the true proportions still show up.
Picture the Sun shrunk down to a beach ball, about 30 centimetres across. On that same scale, Earth shrinks to a pea, just a few millimetres wide. That pea sits about 26 metres from the beach ball, roughly as long as two school buses parked end to end.
A scale model only works if you shrink sizes and distances by the exact same amount. If you shrank the sizes enough to fit the planets on your desk, the distances would need to stretch across a football field, and the planets themselves would shrink to invisible specks of dust.
One scale for both size and distance shows that planets are tiny points scattered across huge stretches of empty space.
More to read
Solar distance
The solar system is mostly empty space. The Sun is about 150 million kilometers from Earth. That distance is called one astronomical unit (AU). Mercury orbits at 0.4 AU. Venus at 0.7 AU. Earth at 1 AU. Mars at 1.5 AU. But then there is a huge gap. Jupiter orbits at 5.2 AU. Saturn at 9.5 AU. Uranus at 19.2 AU. Neptune at 30 AU. The distances between planets are much greater than the sizes of the planets themselves. If the Sun were a beach ball, Earth would be a pea about 26 meters away. Neptune would be a marble nearly a kilometer away.
Circular orbits
Planets do not orbit in perfect circles. Their paths are stretched circles called ellipses. The Sun sits at one focus of the ellipse, not the center. This means planets speed up when closer to the Sun and slow down when farther away. Johannes Kepler discovered this in the early 1600s. His first law says orbits are ellipses. His second law says planets sweep out equal areas in equal times. His third law connects orbital period to distance. The farther a planet, the longer its year. Mercury's year is 88 days. Neptune's year is 165 Earth years.
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2 · Watch
به انگلیسیTake it off screen
Where it sits
Learn first
Optional connections
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.