Observations
What is the relationship between the speed of planets and their distance from the Sun?
The closer the planet is to the sun, the faster it moves around the sun
| Month | Day | Year | |
| Starting time | 9 | 22 | 2019 |
| Ending time | 9 | 22 | 2020 |
Use the starting and ending times recorded above, what is Earth’s orbital period (in Earth years)?
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365 days
The distance units shown on the grid are called astronomical units (AU). Look at Earth’s orbit. How far is Earth from the Sun in AU?
1 AU
| Planet | Mean orbital radius (AU) | Period (Earth years) | R 3 | T 2 |
| Mercury | 0.387 | 0.24 | 0.058 | 0.058 |
| Venus | 0.723 | 0.62 | 0.378 | 0.384 |
| Earth | 1.0 | 1.0 | 1 | 1 |
| Mars | 1.52 | 1.88 | 3.51 | 3.53 |
| Jupiter | 5.2 | 11.86 | 140.6 | 140.66 |
| Saturn | 9.55 | 29.46 | 870.98 | 867.89 |
| Uranus | 19.2 | 84.01 | 7,077.9 | 7,057.68 |
| Neptune | 30.1 | 164.79 | 27,270.9 | 27,155.74 |
What happens to the period as the orbital radius increases?
The periods lengthened.
Look up Kepler’s 3 rd Law and relate it back to your calculations of R 3 and T 2 for each planet. Did you prove the law? Explain why or why not.
The calculations proved Kepler’s 3 rd law because as the distance from the sun increased, the period taken to orbit around the sun increased.
A new planet was discovered! It has an orbital radius of 45.529 AU. Based on Kepler’s 3 rd law, what is the approximate period of its orbit? Show your work and include units with your answer for full credit!
R 3 = T 2
94,379.6 = T 2
T = 307.2 Earth years
| Object | Mean Orbital Radius (AU) | Circumference of Orbit (AU) | Period (Earth Years) | Orbital Speed (AU/year) | Orbital Speed (miles/hour) |
| Mercury | 0.387 | 2.431593 | 0.24 | 10.13 | 107,418.52 |
| Venus | 0.723 | 4.54274 | 0.62 | 7.33 | 77,727.32 |
| Earth | 1.0 | 6.28319 | 1.0 | 6.28 | 66,593.12 |
| Mars | 1.52 | 9.55044 | 1.88 | 5.08 | 53,868.32 |
| Jupiter | 5.2 | 32.67256 | 11.86 | 2.75 | 29,161 |
| Saturn | 9.55 | 60.0044 | 29.46 | 2.04 | 21,632.16 |
| Uranus | 19.2 | 120.6372 | 84.01 | 1.44 | 15,269.76 |
| Neptune | 30.1 | 189.124 | 164.79 | 1.15 | 12,194.6 |
How does an increase in orbital radius affect average orbital speed?
An increase in orbital radius resulted in an increase in orbital speed.
