Planetary Conjunctions: Alignments in the Sky
draft readiness: experimental EarthSky Orbits ASTR101 8 min
Core demo behavior is implemented, but parity and launch-gate signoff are still pending.
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This exhibit's copy was imported from the legacy ASTR101 SP26 demos and has not yet been
fully reviewed against the current instrument UI, units, and exports.
Predict
Predict
When Earth and a planet line up (a conjunction), will that planet stay near the Sun in our sky for long? Why or why not?
Play
Play
- Advance time to find a conjunction and an opposition.
- Compare where the planet is in space to how close it appears to the Sun in the sky.
- Measure the time between two conjunctions and describe the pattern you see.
Explain
Explain
Use relative motion to explain why the time between conjunctions is different from a planet’s orbital period.
Learning goals
- Define conjunction and opposition as seen from Earth.
- Explain why conjunctions repeat using Earth’s motion relative to another planet.
- Use the model to estimate the time between successive conjunctions (synodic period).
Misconceptions targeted
- A conjunction means the planets are physically close together in space.
Model notes
- The model is schematic (not to scale) and focuses on geometry and timing rather than precise ephemerides.
About this demo
Explore how conjunctions and oppositions are line-of-sight alignments caused by relative motion, and estimate how long it takes for the same alignment to repeat.
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