Why is only one side of the moon always visible from Earth?
People come and go in our lives. Usually, we say that there are no constants in life. But in reality, there are plenty of constants and one such constant is the side of the Moon that is always facing Earth.
We can for sure say that our grandparents, our grandkids, and their grandkids will see the same side of the Moon when they glance into the beauty of the sky. Ever wondered why it is so?
It is easy to think that Moon is stuck like that, out there in the void of space. But that is not the case. Just like Earth, Moon also rotates on its axis. Just like how Earth revolves around the Sun in 365 days, Moon revolves around Earth in 27.3 days. What is interesting is that it takes Moon the same 27.3 days to rotate on its own axis.
Because it this equality in time periods of Moon’s revolution and rotation, it feels as though Moon is stuck in its orbit, with the near side always facing us. Another name for this phenomenon is tidal locking. Gravitational forces exerted by the Moon gently warp Earth’s shape, creating a slight bulge from the center. This gives us the tides. Similar Earth’s gravity also affects Moon, slowing it down permanently locking the near side to face us.
It is believed that tidal locking happened around 4 billion years ago and ever since that Earth has only seen one side of the Moon. It is worthwhile to note that all of our manned missions to the Moon have been to the near side. The reason for this is that the line of sight provides ground for better communication. But we have explored the farther side of the Moon through various remote missions.
Soviet Luna 3 was the first man-made object to capture the far side back in 1959. It took us almost another decade from there to view the side through human eyes when Apollo 8 orbited the Moon in 1968. The farther side is referred to as the darker side of the Moon even though it receives almost the same amount of sunlight as the near side.
Highlands on the farther side is composed of a mineral called feldspar while the near side has basins filled with Mare deposits. Scientists believe that the Mare deposits have come earlier magma risings as the crust of the Moon is much thinner on the near side.