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How Astronomers Know — Evidence Lab

Modeling an Orbit with Mathematics

Estimated time
~30 min
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Learning goals
  • For any object orbiting the Sun, T² = a³ (T in years, a in AU). This mathematical model applies from Mercury to Neptune to newly discovered dwarf planets.
  • HS-ESS1-4 — Students apply Kepler's laws to solar-system data.
Help & glossary
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Question 1 of 3

Mars orbits the Sun at a semi-major axis of about 1.524 AU. Using T² = a³, estimate Mars's orbital period in Earth years.

Kepler's third law lets us convert between orbital distance and orbital period using very simple math when we use AU and years.

years

    Sources