How long is a day on the moon?
A day on the Moon is 27 days, 7 hours, and 43.2 minutes long (in Earth time). This is how long the Moon takes to complete one full rotation on its axis. The reason why a day on the Moon is so long is because the gravitational forces between Earth and the Moon slowed the Moon’s rotation until the same side of the Moon always faced the Earth. This means that one day on the Moon lasts for the same amount of time that it takes for the Moon to make one complete orbit around Earth.
on its axis, then one lunar day is about 27.32 Earth days long. However, if we consider the perspective of an observer standing on the moon, then a day is the amount of time between two sunrises (or sunsets, or noons; from any point, around and back to the same point). In this case, a lunar day lasts about 29.5 Earth days. This is usually the definition that astronomers prefer.
