# Midterm Problem 108-1

#### [Back to Introduction to Astronomy](https://hackmd.io/@sophie8909/Hkhh8G1vH)
###### tags: `NTNU` `通識` `Science and Life` `Introduction to Astronomy`

## Hint
- How long does it take to rotate around the sun if the planet is at 9AU?
- a=9AU
- P^2^ ~ 9x9x9
- P ~ $\sqrt{729}$ ~ 27 yrs
- $P^2=\dfrac{4\pi^2}{GM}a^3$