Did last Tuesday seem like a long day? It wasn't your imagination. Tabitha M. Powledge explains why an extra second was added to that day, and others from time to time: "Leap seconds have been inserted into our timekeeping 25 times, at first nearly annually. But, also for reasons not completely understood yet, it’s happened much less frequently since 1999." Also, New York Times science writer Gina Kolata wins praise for a series on new developments in cardio medicine.
July 4, 2015
