On May 10, 4:30-9PM, the Clay Center at Dexter Southfield School and the Amateur Telescope Makers of Boston will celebrate National Astronomy Day with a public festival of science that includes a schedule of over 50 fun activities such as solar and night telescope viewing, observatory tours, planetarium shows, laser light shows, kite flying, model rocketry, guest lecturers including “Galileo,” NASA/JPL ambassadors, telescope clinic, and hands-on activities.   Most activities are free, but the laser light show and planetarium require purchased tickets.  Register for the festival — and purchase tickets for the ticketed events — online.  The festival is open to all ages (those under 12 must be supervised) and will take place at the Clay Center, 20 Newton Street, Brookline.