Summer is great for milky way viewing, a night when the moon is not full or is absent during some of the period between sunset and sunrise is best. Even in summer if you check the weather patterns and moonrise, moonset you can find great dark skies. If you arr trying to come out for meteor shower viewing, if a campspot is not abailable on the peak of the shower, then try for a spot within a couple days before or after. You need to have a camping spot in order to be in the park after sunset for all night astronomy viewing. Reserve it ahead of time, even in August the campgrounds are filling up during a new moon. Check the parks official website or call for more information.
The closer to a new moon it is, the better, but the park has some of the darkest skies in the state, so there's no bad time to go.
You can check out this calendar to see what cool stuff is happening with the stars and decide on the best time to visit. If your schedule allows you to camp on the night of a meteor shower, you’ll have a great time! http://www.seasky.org/astronomy/astronomy-calendar-current.html Otherwise
I went there a few months ago and it was perfect. I believe anytime you go would be great.
Best time close if not on a New Moon and cooler nights.
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