1. Starlight bends — but how much? Einstein performed a series of calculations to determine the size of the predicted shift but initially muffed the effort, arriving at a number that was half the correct value. Had the astronomers managed to test this number in their initial eclipse-viewing efforts, their observations wouldn’t have matched his prediction. But their attempts were stymied by weather in 1912 and by war in 1914. By the time they made the necessary observation, in the spring of 1919, Einstein had corrected his blunder — and astronomers saw exactly the shift that he had predicted. 2....