The Bortle Scale measures how dark a sky is, and it's one of the most important factors for considering whether or not you'll be able to observe stars in the night sky. If you're planning a trip to Joshua Tree National Park for stargazing, you may be wondering what the Bortle Scale rating is in the Park. The good news is that Joshua Tree National Park has an incredibly dark sky, with a Bortle Scale rating of 2 on the Dark Sky Scale!