A day on the moon is the same as a year on the moon.
“A lunar year is actually defined by the time it takes the moon to travel around the earth…. Now, the moon only rotates once on its axis as it rotates around the earth. It takes 27-1/2 earth days for the moon to rotate around its axis one time. So a moon day is 27-1/2 earth days. That is also how long it takes for the moon to rotate around the earth. That’s a moon year. So the length of time it takes for the moon to spin around on its axis once is the same amount of time it takes the moon to spin around the earth once. A day is defined by the amount of time it takes a satellite to spin around on its axis. For the moon, that’s 27-1/2 days. A year is defined by the amount of time it takes a planet to spin around the celestial body that is holding it in its orbit. For the earth, that’s the sun; for the moon, that would be the planet Earth. It also takes 27-1/2 days for the moon to rotate around the Earth. 27-1/2 days to spin around on its axis (one day has passed) and 27-1/2 days to rotate around the Earth (one year has passed). It’s why we only see one side of the moon.”