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The Solar System Cheat Sheet
A printable reference covering planet order, orbits, gravity, rotation, revolution, moons, asteroids, comets, and scale for grades 6-9.
The solar system includes the Sun, eight planets, dwarf planets, moons, asteroids, comets, and smaller objects held together by gravity. Students need this cheat sheet to remember planet order, compare object types, and understand how motion in space works. It also helps connect everyday patterns, such as day and year length, to rotation and revolution. Clear formulas and definitions make solar system questions easier to solve and explain. The most important ideas are that planets orbit the Sun in elliptical paths, gravity controls orbital motion, and distance affects how strong gravity is. Rotation is spinning on an axis, while revolution is movement around another object. The planets are grouped into rocky inner planets and gas or ice giant outer planets. Scale is also important because the solar system is much larger than classroom diagrams usually show.
Key Facts
- The eight planets in order from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
- A mnemonic for planet order is My Very Educated Mother Just Served Us Noodles.
- Rotation means an object spins on its axis, and one full rotation of Earth takes about 24 hours.
- Revolution means an object orbits another object, and one full revolution of Earth around the Sun takes about 365.25 days.
- Average speed equals distance divided by time, so speed = distance / time.
- Gravity gets weaker as distance increases, and the relationship is gravity strength is proportional to 1 / distance squared.
- The inner planets, Mercury through Mars, are small rocky planets, while Jupiter through Neptune are large outer planets made mostly of gas or ice.
- One astronomical unit, 1 AU, is the average distance from Earth to the Sun, about 150 million kilometers.
Vocabulary
- Solar system
- The solar system is the Sun and all objects that orbit it, including planets, moons, dwarf planets, asteroids, and comets.
- Orbit
- An orbit is the curved path one object follows around another object because of gravity.
- Astronomical unit
- An astronomical unit, or AU, is the average Earth-Sun distance, about 150 million kilometers.
- Rotation
- Rotation is the spinning motion of an object around its own axis.
- Revolution
- Revolution is the motion of one object traveling around another object.
- Dwarf planet
- A dwarf planet is a nearly round object that orbits the Sun but has not cleared its orbital path of other objects.
Common Mistakes to Avoid
- Confusing rotation with revolution is wrong because rotation causes day and night, while revolution around the Sun helps define a year.
- Listing Pluto as one of the eight planets is wrong because Pluto is classified as a dwarf planet, not a major planet.
- Drawing planets evenly spaced is misleading because the distances between planets grow much larger in the outer solar system.
- Thinking seasons happen because Earth is closer to or farther from the Sun is wrong because seasons are mainly caused by Earth's tilted axis.
- Assuming larger planets are always closer to the Sun is wrong because planet size and distance from the Sun are separate properties.
Practice Questions
- 1 List the eight planets in order from the Sun.
- 2 If a spacecraft travels 600 million kilometers in 300 days, what is its average speed in million kilometers per day?
- 3 Earth is about 1 AU from the Sun and Mars is about 1.5 AU from the Sun. About how many million kilometers from the Sun is Mars if 1 AU is 150 million kilometers?
- 4 Explain why a classroom diagram of the solar system usually cannot show both planet sizes and planet distances accurately at the same scale.