“What is a Vernal Pond?”  at Thacher Park. 10 a.m. Vernal ponds are ephemeral wetlands that fill with water from winter and spring rains, and usually dry out by the end of summer. Come try your hand at citizen science, and discover why vernal pools are known to be the coral reefs of the northeastern forest. Appropriate for ages 8 and older. Call 518-872-0800 to register and for meeting place. Park entrance fee is $6 per vehicle.