September 12 is the second-ever International Night of Skyglow Observation, an official event of UNESCO's "International Year of Light". Around the world, citizen scientists will observe how much light pollution is in their community by looking at the stars. The link above is a very short tip on how to do it.
In Berlin we'll be holding a special event that night, a Flashmob for Science, in which many people will show up to make observations simultaneously at a single location. The flashmob will take place in Park am Gleisdreieck at 21:30 on September 12. More details will be on the Facebook Event page. If you plan to come, please sign up there so that we can communicate with you (e.g. in case of cancellation due to rain).
Here's a map, we will do the observation right on the spot marked by the pine tree.
Hope to see you there!