Boston’s Museum of Science hosts a free drop-in activity, Astronomy After Hours, for Grades PreK-12 and adults. Weather permitting, it takes place in the Gilliland Observatory on the roof of the Museum’s parking garage (map). If the sky is clear, you can view stars and planets, and if it’s cloudy there will be tours and hands-on activities inside the observatory. It’s on Fridays in September (8-10:30PM) and October (7:30-9:30PM), returning again in mid-April through June, and on both Thursdays and Fridays in July and August. This popular program can get crowded, particularly in summer, and in this case time for attendees may be limited to about 20 minutes. Arrive at least 30 minutes before the scheduled end of the program to ensure a place in line. For more information and the impact of weather on the evening’s program (updated by 5:30PM on days of the program), call 617-589-0267.