The Swift-Tuttle comet, the largest comet known to repeatedly pass by Earth, will be visible. Bring an item for the snack/dessert potluck. Registration required. Event: free. Parking: $7. 6:30–9:30 p.m. North Sonoma Mountain Regional Park & Open Space Preserve. 5297 Sonoma Mountain Rd., Santa Rosa. Register online: tinyurl.com/yy9fxk2a.