Yes, anyone living on the Moon will experience night and day, but a lunar day and night would last almost an entire Earth month.

Earth’s gravity causes the Moon to elongate slightly on the sides nearest and farthest from us. The gravitational forces acting differently on the near and far side of the Moon’s ‘bulge’ creates a torque that acts to alter the Moon’s rotational period so that it matches its orbit period. This is known as ‘tidal locking’.

Because the Moon spins in the same time as it orbits Earth, it only ever presents the same face to us. But even though the Moon is ‘tidally locked’ to Earth, it’s still rotating with respect to the Sun. Its rotation period is 29 days, 12 hours and 44 minutes (also the length of the ‘lunar month’ on Earth). So, a lunar colonist would experience about two weeks of daylight, followed by about two weeks of night.

Of course, from the nearside of the Moon, Earth appears to stay in exactly the same position in the sky while the stars rise and set — although Earth’s exact position depends on where you are on the Moon. The phase of Earth will change, just like the Moon’s does, over a lunar month, but Earth itself will be seen spinning once in a little over 24 hours.

Earth would be fully illuminated (a ‘full Earth’) in the middle of the lunar night, while at ‘new Earth’ it would be almost hidden in the glare of the Sun and showing its unlit, night-time hemisphere. Since Earth is about four times the size of the Moon, solar eclipses visible on the Moon last much longer than on Earth. Every time people on Earth see a total lunar eclipse, anyone living on the Moon would see a total solar eclipse.

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Asked by: Fred Vernon, via email

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