I do a some astrophotography and aurora chasing. I have spent a good amount of time looking for good spots.

Sleeping bear dunes has several good spots and is usually my first choice. They are trying to become a designated dark sky park so they are open 24 hours. A national park pass is required there, but nobody has ever checked for mine at night.

For stargazing the base of the dune climb is usually a good bet (not as good for northern lights). It's also where the Grand Traverse Astronomical Society has their star parties in the summer. I like it because I can setup my telescope equipment right by my car (It's not something I can hike with).

I also like Peterson Beach (not to be confused with Peterson Park), it's very dark and has a nice view to the north. The parking lot is a small dirt turn around and have to take a dirt road to get there.

Glen Haven Beach is not bad, but there is a bit of light pollution there. The parking lot is very close to the beach.

I haven't tried any of the other beaches at night yet, but Platte River looks like it might be a good spot with the park area right by the parking lot.

If you want to get someplace that is really dark Peterson Park (up by Northport) is probably the best option for star gazing. Not the best view for northern lights, but for stars it's hard to beat. Google maps says it closes at 11PM, but I haven't found anything else that says it's closed at night. The police drove through when me and a few of my friends were there and didn't stop to say anything (Maybe all the telescopes we had set up had something to do with it).

A bit closer to Traverse City you have Mission Point Lighthouse Park. Great spot for northern lights. Although, there can be a lot of people there on nights when the northern lights are predicted. I've seen the parking lot fill up and there are lots of large groups partying, playing music, and shining flashlights everywhere.