One Day on Mercury Lasts Two Mercury Years

Mercury races around the Sun but turns slowly on its axis, and the combination produces a very strange calendar. NASA states that Mercury completes one rotation every 59 Earth days. Because it is also moving quickly along its orbit, one Mercury solar day, meaning one full day-night cycle, equals 176 Earth days. That is just over two years on Mercury, since the planet circles the Sun every 88 Earth days. A long day means long heat and long cold. NASA says daytime temperatures on Mercury can reach 800 degrees Fahrenheit, or 430 degrees Celsius, while nights, with no atmosphere to hold the heat, can drop to minus 290 degrees Fahrenheit. Mercury may even have water ice. NASA says it could survive at the poles, inside deep craters that stay in permanent shadow.