Planetary Motion
Elementary School
Definition
The movement of planets as they orbit the Sun and rotate on their axes. Orbits are shaped by gravity, and a planet's rotation produces day and night while its revolution around the Sun produces its year.
Worked examples
Earth rotates once every 24 hours, giving us day and night, while it revolves around the Sun once every 365.25 days, giving us a year.
Rotation creates the daily cycle; revolution determines the length of a year.
Mars takes 687 Earth days to complete one orbit around the Sun because it is farther from the Sun than Earth.
Planets farther from the Sun have longer orbital periods due to the greater distance they must travel.
Common mistakes
- The Sun orbits Earth → Earth and other planets orbit the Sun Gravity from the Sun's large mass keeps planets in orbit around it, not the reverse.
- Rotation and revolution are the same thing → Rotation is spinning on an axis; revolution is orbiting the Sun Rotation produces day/night; revolution produces the year.
- All planets take the same time to orbit the Sun → Each planet has a different orbital period depending on its distance from the Sun Farther planets travel longer paths and move slower, so their years are longer.
Where you'll use it next
Planetary motion is foundational for studying Kepler's laws, gravitational forces, satellite orbits, and understanding seasons, eclipses, and how we measure time and navigate in space.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026