Why Do We Only See One Side Of The Moon? Astronomy Facts For Kids

There have been six crewed missions to the Moon, and none have landed on the far side.

The Moon takes one lunar month to orbit the Earth and plays a vital role in stabilizing our planet’s environment. It also moderates Earth’s climate and causes oceanic tides.

It is the only celestial body besides our home planet where humans have set foot. It is the brightest and the largest shining object in our night sky. The distance between the Earth and the Moon is accurately measured with the help of a laser beam. How does that work you may ask? Well, during the Apollo mission, the astronauts placed reflectors on the Moon's surface which can reflect laser beams back toward the Earth's surface. The time it takes the beam to travel back is used to calculate the distance. The Moon is tidally locked to the Earth and causes synchronous rotation despite its elliptical (oval-shaped) orbit. Humans have only remotely explored both sides of the Moon through various satellites.

If you enjoy learning fun facts with Kidadl, why not check out some more articles such as winter facts and why do seasons change?

What is the synchronous rotation of the Moon?

Did you know that the Moon used to rotate much faster than it does today? So, what caused it to slow down? Why is the Moon's rotation axis not at a right angle to its orbit? And is it just a coincidence that the moon’s rotational and orbital period is the same?

The phenomenon in which only one side of a celestial object is visible as it orbits around another celestial object is known as synchronous rotation or tidal locking. The Moon’s rotational period and orbital period are synchronized, which means that the Moon orbits around the Earth every 27.3 days and spins once on its axis during this period.

A billion years ago, when the moon’s rotational pace was much faster, these forces would cause constant stretching and squeezing on the Earth and the Moon due to tidal friction. While this causes high and low tides on the Earth, a similar effect on the Moon led it to slow down its speed over time. The orbital time became the same and the tidal friction on the Moon came down to zero. Today it revolves and rotates on its axis at exactly the same time. This stabilization of the Moon's rotation speed has led to the synchronous rotation of the Moon around the Earth.

Why is only one side of the Moon visible from the Earth?

The Moon never turns its back on the Earth and we don’t ever see its far side, which may make you wonder if the Moon rotates at all! Well, if the Moon was fixed at one place without any rotation, we would see all of its sides as it orbited us. When viewed from Earth, the far side of the Moon is not visible because of how the Moon spins. Only the near side faces towards the Earth at all times. Hence, we only get to see the same half of the Moon.

The only reason celestial objects stay in their orbit is because gravitational forces are acting between them. For example, all the planets revolve around the sun due to its gravitational pull. A similar force is at work between the Moon and the Earth and is strongest at the point on Earth closest to the Moon and weakest at the farthest point. While the Moon’s gravitational pull on the Earth causes high and low tides, Earth’s gravitational pull on the Moon causes a distortion in the Moon’s shape which leads to a small lunar oscillation known as lunar liberation. This means that the Moon takes the exact same time to orbit around the Earth and rotate on its axis. Over time, this force led to the synchronous rotation of the Moon, which is the reason why only one side of the Moon is visible from Earth.

How many sides does the Moon have?

Did you know that a day on Earth is 24 hours because of the Moon? The Moon has two sides, the nearside that is visible from the Earth and the unseen and lesser-explored far side also known as the dark side of the Moon. We only see one side of the Moon as it is tidally locked to the Earth.

The near side is the side facing the Earth, which is ironically slightly darker than the far side (dark side) of the Moon. No one has ever been to the far side of the Moon due to communication requirements. However, we have been able to capture it in image. The Soviet spacecraft Luna 3 was the first to click the grainy image of the far side. Ever since then a lot of detailed information has been gathered and scientists have made detailed maps and images of the other side of the Moon. You’ll be shocked to know that both sides look very different in these images!

While the near side of the Moon is darker due to large basins filled with dark basalt, the far side is made up of a lighter colored element known as feldspar. Another major difference in the appearance of the two sides is the difference in the crust density. The crust is thinner on the near side which means that the mantle of the near side is closer to the surface. Therefore that side is more crated due to asteroids from space.

What part of the Moon is visible from the Earth?

The nearside is the lunar hemisphere of the Moon that is visible from the Earth. It is the more explored and visited side. If we only see one side then you may wonder why the Moon appears to be different throughout the month.

As we briefly discussed earlier, the Earth’s gravity causes a distortion in the Moon’s shape which leads to a torque that causes the Moon to incline towards the Earth. This causes a wagging of the Moon that can be seen from the Earth over the course of a month. This leads to the phenomenon known as lunar liberation. Due to these liberations, we can see more than 50% of the Moon during one lunar cycle. We can see the North pole and the South pole of the Moon from the same angle during different points of time. Due to these liberations, we are able to view about 59% of the Moon’s surface despite the tidal locking. There are two major types of liberations. There is the diurnal (daily) liberations in which the Moon appears to be turning from west to east, and then there's the longitudinal liberations in which the Moon seems to be turning from east to west.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for why do we only see one side of the Moon then why not take a look at why do we have day and night, or zodiac facts.