How to Calculate Kepler Third Law
What is Kepler Third Law?
Kepler's third law relates orbital period to orbital distance. It explains why planets farther from the Sun take longer to orbit.
Formula
The calculator applies T² = (4π² / GM) × a³
- GM
- GM value — Variable used in the calculation
Step-by-Step Guide
- 1Enter orbital period and distance, or the central body's mass
- 2The calculator applies T² = (4π² / GM) × a³
- 3Results show orbital relationship
Worked Examples
Input
a = 1 AU (Earth orbit), M = 1.989 × 10³⁰ kg (Sun)
Result
T ≈ 1 year
By definition
Common Mistakes to Avoid
- ✕Using incorrect AU values or unit conversions
- ✕Confusing period with frequency
Frequently Asked Questions
Does Kepler's law apply to all objects?
Yes, it applies to any orbit around a massive central body, from planets around stars to satellites around planets.
Why is period proportional to distance to the 3/2 power?
Gravity weakens with distance, requiring slower speeds at greater distances, which more than compensates for longer path length.
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