As the sun dipped below the horizon on a late summer weekend in 1924, anticipation hung thick in the air. On August 23, in cities across the globe, people gathered eagerly around curbside telescopes, their eyes fixed on the red planet that had captivated imaginations for decades. Mars, closer to Earth than it had been in a century, promised an unprecedented view of its enigmatic surface. “Witness the wonders of Mars!” proclaimed sidewalk astronomers in New York City. “This is your once-in-a-lif...