an artist's concept of the exoplanet WASP-43b Anyone who likes to exercise outside can tell you the sunrise side of the day is far cooler than the evening twilight. Here on Earth, with our rotating world, this is easy to understand. Throughout the night, our planet radiates away the heat of the day to outer space and that cooler part of the planet then rotates back toward day. This is an imperfect process, but it is efficient enough that I’m willing to bike ride in the early morning light even in the peak of an Illinois summer. For tidally locked worlds, this kind of a night time cooling...