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When 8-10 p.m. Saturday • Where Gateway Arch National Park; meet at south Arch leg • How much Free • More info nps.gov/jeff

Volunteers from the St. Louis Astronomical Society will help visitors use telescopes to take a peek at moon craters, Venus and other celestial objects. And rangers will discuss the transformation of the grounds over the years — from French fur-trading post, to warehouse district, to national park. Rain or clouds may affect this event, so call 314-655-1750, ext. 472, before you go. Another Arch stargazing event is May 26.