A lunar day is the time it takes for the Moon to complete one rotation on its axis. This is about 27.3 Earth days. However, the Moon also orbits the Earth every 27.3 Earth days. This means that the time it takes for the Moon to return to the same phase in the sky is about 29.5 Earth days. This is what is called a synodic month.

 A lunar day is the time it takes for the Moon to complete one rotation on its axis. This is about 27.3 Earth days. However, the Moon also orbits the Earth every 27.3 Earth days. This means that the time it takes for the Moon to return to the same phase in the sky is about 29.5 Earth days. This is what is called a synodic month.

So, why do people say that one moon day is 14 Earth days? It's because the Moon's day and night are each about 14 Earth days long. This is because the Moon's rotation is tidally locked to the Earth. This means that the same side of the Moon always faces the Earth. As the Moon orbits the Earth, the side that faces the Earth is exposed to sunlight for about 14 Earth days, and then the other side is exposed to sunlight for the next 14 Earth days.

So, while a lunar day is not 14 Earth days long, the Moon does experience days and nights that are each about 14 Earth days long.

A lunar day is the time it takes for the Moon to rotate once on its axis. However, because the Moon is also orbiting the Earth, the time it takes for the same point on the Moon to face the Sun is slightly longer. This is called a synodic day, and it lasts about 29.53 days.

The reason why the synodic day is longer than the sidereal day is because the Moon is moving around the Earth as it rotates on its axis. So, even though the Moon rotates once on its axis every 27.3 days, it takes about 2.2 days longer for the same point on the Moon to face the Sun again.

This difference in time is what causes the lunar phases. As the Moon orbits the Earth, different amounts of the Moon's surface are illuminated by the Sun. This is what creates the waxing and waning of the Moon that we see from Earth.

So, to answer your question, one moon day is not actually 14 Earth days. A lunar day is 27.3 days, but a synodic day, which is the time it takes for the same point on the Moon to face the Sun, is about 29.53 days.

The Moon's rotation and orbit are both very slow. The Moon takes about 27.3 days to complete one rotation on its axis, and it takes about 27.3 days to complete one orbit around Earth. This means that the same side of the Moon always faces Earth.

A lunar day is the amount of time it takes for the Moon to rotate once on its axis. Because the Moon's rotation is so slow, a lunar day is actually about 29.5 Earth days long. This is because the Moon takes about 2.2 days to move around Earth enough to be in the same position relative to the Sun.

So, why do people say that one Moon day is 14 Earth days? It's because the Moon's rotation and orbit are so closely linked. The Moon's rotation is tidally locked to Earth, which means that the Moon's rotation rate is synchronized with its orbital rate. This means that the same side of the Moon always faces Earth, and it also means that the Moon's day and night cycle are the same length as its orbital period.

In other words, the Moon's day and night cycle are 29.5 Earth days long. So, when people say that one Moon day is 14 Earth days, they're really talking about the length of the Moon's day and night cycle.

Here's a diagram that might help to make this a little clearer:

[Diagram of the Moon's rotation and orbit]

The Moon's rotation (red arrow) is very slow, and it takes about 27.3 days to complete one rotation on its axis. The Moon's orbit (blue arrow) is also very slow, and it takes about 27.3 days to complete one orbit around Earth.

The Moon's rotation and orbit are closely linked, which is why the Moon's rotation rate is synchronized with its orbital rate. This means that the same side of the Moon always faces Earth, and it also means that the Moon's day and night cycle are the same length as its orbital period.

In other words, the Moon's day and night cycle are 29.5 Earth days long. So, when people say that one Moon day is 14 Earth days, they're really talking about the length of the Moon's day and night cycle.