In describing his upcoming trip to the Moon, and as portrayed in the movie Apollo 13 (Universal, 1995), astronaut Jim Lovell said, “I’ll be walking in a place where there’s a 400-degree difference between sunlight and shadow.” What is it that is hot in sunlight and cold in shadow? Suppose an astronaut standing on the Moon holds a thermometer in his gloved hand. Is it reading the temperature of the vacuum at the Moon’s surface? Does it read any temperature? If so, what object or substance has that temperature?