A day on Moon is approximately 29 and half day on Earth. We only see 59% of the Moon’s surface. When the Moon was formed, its rotation speed and orbit was much more different than it is now. Over time, due to Earth’s gravitational force, the rotation speed of the Moon got decreased. We are familiar with the fact that rotation of Moon causes tidal effects on the Earth. So, imagine what effect Earth’s gravitational field could have on Moon if the Earth is 81 times more massive than the Moon!
The Earth tends to pull all the mass of the Moon to one side. Also, the effect of Earth’s gravitational field is stronger on the side facing the Earth as compared to the other side. The Moon’s gravitational field also affects the surface of the Earth. This causes stretches, resulting in tidal effects on both the bodies.
Moon Surface – Why Fifty-nine Percent?
The fact that we get to see only 59% of the Moon’s surface and not exactly 50% is that the Moon’s orbit around the Earth is not perfectly circular. It is more of an ellipse, and as the Moon rotates around the Earth, it’s gular speed varies, but the rotational speed remains the same.
Due to Earth being larger than the Moon, some part of Earth’s momentum gets shifted to the Moon to maintain the law of conservation of momentum. This causes Moon’s orbital radius to increase up to 3.8 centimeters every year. Some significant geological changes are taking place because of this phenomenon.
According to theories, some billions of years later, the same side of Earth will always face the Moon. The Moon’s rotational speed will reduce down further that one day on Moon will be approximately equal to 57 days on the Earth. But also according to theories, billions of years later, Sun will consume both Earth and Moon. Also, the residents of Earth will have to find a new home!
