A few notes

Wear appropriate clothing for standing inactive out of doors.
If you own a telescope or a good pair of binoculars, please bring one or more along.
Carry only necessities. We are gathering at night, and the world is an imperfect place.
Meeting outdoors late at night is logistically different than meeting indoors; sometimes an event ends early for any one of a few logical reasons. Sincere apologies, should you arrive to a gathering that has broken up early.
Guests are welcome. Hope to see you there!

Weather considerations

Star-gazing requires clear skies. Even a light fog can be sufficient to drive a sky watcher indoors. To determine whether it will be worth your trip to come, step outside, and look up into the sky. If you can see at least three or four sharp, bright points in the sky, the event is likely taking place. If not, go enjoy a movie or a good meal, and we'll see you next time.

Don't walk into the viewing area with a flashlight. It takes nearly a half an hour for vision to adjust to the dark. A single flashlight will quickly ruin everyone's night vision. If you need to see what you are doing, or where you are going, bring a low brightness, red-filtered flashlight, and keep it pointed down. The same precautions hold true for cigarette lighters.
Take a fair turn at the telescopes, and be generous with your own equipment. The point of gathering as a group is to enjoy the company as much as the sky.
If you can't bring a telescope, try to bring a snack, or cups and a thermos of hot drinks. Those carrying telescopes usually have their hands too full to also carry a hot beverage. Same goes when leaving. Offer to carry garbage out, so that those carrying telescopes aren't left with more to carry.
A step-stool will be available for children to stand on. It is inappropriate to lift a child up to a telescope, as it will almost certainly shift the scope off of the object being viewed. Similarly, if your child is not old enough to appropriately handle delicate equipment, he or she shouldn't be. With these caveats, children are warmly welcomed to attend.
The unwooded areas of Prospect Park are officially open until 1 a.m. A small gathering does not require a permit. However, park security or police may attempt to enforce laws that don't exist. Allow the gathering organizer to speak with officials questioning activity.