Cube3D 立方体数理Space · Primary school / Middle school
Why is a year different on each planet?
A year is the time a planet takes to complete one orbit around its star. It is not a fixed duration shared by every planet. Earth takes about 365.25 days to orbit the Sun, while Mercury takes about 88 Earth days. A single classroom clock helps make that contrast visible.
Watch two planets on the same clock
Open the planetary-orbit lab. Its current controls are in Chinese; the model can still be used alongside this English guide. Locate Earth and Mercury, choose a comfortable viewing angle, and start the same simulation clock for both planets.
Predict how many circuits Mercury will complete while Earth completes one. Speeding up time changes how quickly both move on screen; it does not give each planet a different clock. Count Mercury’s circuits while following Earth back to its starting position.
Turn an observation into a ratio
Divide Earth’s approximate orbital period by Mercury’s: 365.25 ÷ 88 ≈ 4.15. Mercury completes just over four orbits during one Earth year. The result compares durations; it does not tell you the ratio of the planets’ physical sizes.
A planet’s orbital period depends on its orbit and the central mass. For planets orbiting the Sun, the more distant planets generally take longer. This model is useful for comparing that timing, but its visible sizes and orbital spacing should not be used as a scale drawing.
Check your understanding
A visitor increases the simulation speed. Does Mercury now have a shorter year relative to Earth, or do both years simply pass faster on the screen? Explain using the shared clock.
Show the explanation
Both years pass faster on screen. The ratio of the orbital periods remains the same because the same time multiplier applies to both planets.
What the model assumes
The model compares approximate orbital periods, not live sky positions or spacecraft navigation. Displayed planet sizes and spacing are adjusted for visibility.