The solar system (age 11+)
Describe the detailed structure of the solar system, including moons, asteroids, and comets, compare orbital periods and distances of the planets, and distinguish between planets, dwarf planets, and other bodies
What a learner can do afterwards
- Names the eight planets in order and gives one distinguishing fact about each
- Describes the difference between a planet, a dwarf planet, an asteroid, and a comet
- Explains the relationship between distance from the Sun and orbital period (planets further out take longer)
The lesson
You already know the eight planets and their order from the Sun. But planets are not the only things orbiting out there. Moons circle planets. Asteroids and comets travel their own paths. Round worlds called dwarf planets orbit too, out past Neptune.
A planet is a large, round object that orbits the Sun and has cleared other objects out of its path. A dwarf planet, like Pluto, is also round and orbits the Sun, but it has not cleared its neighborhood of other debris. Asteroids are smaller, rocky objects, often oddly shaped, that never grew round. Comets are balls of ice and dust. When a comet gets close to the Sun, some of its ice turns to gas and forms a glowing tail.
Mia compares two neighbors. Mars, the fourth planet, finishes one orbit in about two Earth years. Neptune, the eighth planet, takes about 165 Earth years for a single orbit. Neptune sits far more distant from the Sun, so it has a much longer path to travel.
To tell a planet from a dwarf planet, ask one question: has it cleared its neighborhood of other objects? If yes, it's a planet. If no, it's a dwarf planet, even if it's round.
Beyond the eight planets, the solar system holds moons, dwarf planets, asteroids, and comets, and the farther an object orbits from the Sun, the longer its year takes.
Watch it
Where it sits
Learn first
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.