Ever wonder why we can only see one side of the moon? That's because the moon is so close to the earth that the side of the moon facing us is subject to the earth's stronger gravitational pull, and the moon's rotation takes as long as the earth's revolution, which makes the moon tidally locked by the earth.

In fact, many of the exoplanets we've discovered appear to be tidally locked by their parent stars. Some of them are even in the habitable zone within their star system. These exoplanets are not without the potential for life, but unable to support life.

Just imagine if Earth was tidally locked by the sun, how long could you live before extreme weather made Earth uninhabitable? When one side of the planet begins to be exposed to the sun and the other enters perpetual night, everything on Earth will change – from climate patterns to the makeup of water, the most immediate effect of tidal locking is the disappearance of day and night. Have you ever had the experience of burning your skin after staying in the sun for a long time? This is what happens every day on the sunny side. The sun will continue to scorch the sun-facing side of the earth until the temperature is so high that no life can survive.

How high will the temperature be? Depending on how close we are to the sun, it will most likely be above 100 degrees Celsius (212 degrees Fahrenheit) – the temperature that boils water. Such high temperatures would evaporate all the water in the hottest regions of the planet. On the other hand, the temperature on the far side of the Earth will be well below 0 degrees Celsius (32 degrees Fahrenheit), making all the water freeze.

Even if the atmosphere on the cold side is not completely frozen, the cold air will sink, causing the air pressure to rise.

The atmosphere on the other side would be constantly exposed to sunlight, continuously heated and dissipated, causing the pressure to drop.

The dramatic difference in air pressure between the two sides will result in nasty storms all over the planet, and you'd better grab something if you don't want to be blown away.

We should be thankful that the atmosphere was not completely lost in such a harsh environment. Without the atmosphere, human beings would have ceased to exist. The atmosphere is an important part of sustaining life on Earth because it regulates the distribution of heat on the planet.

The only place on Earth's surface where life could exist would be at the edge where day and night meet. But considering that 71% of the Earth's surface is covered by water, it's unlikely that some habitable land will emerge from this edge meeting.

Humans should feel lucky that the Earth will not be tidally locked by the sun for a short period of time, and we are far enough away from the sun that the sun's gravity will not capture one side of the earth.

But the rotation of the earth is slowing down. What if the earth stops rotating completely one day?

related information

Tidal locking occurs when a gravitational gradient keeps celestial bodies always facing the same side of another celestial body; for example, the Moon always faces the same side towards Earth. A tidally locked body takes the same amount of time to revolve around its own axis as it does to revolve around its companion. This synchronous rotation results in a constant hemisphere orientation toward the partner.

The result of tidal locking is that the period in which the moon rotates on its axis is about the same time as the period in which it orbits the planet. Excluding the influence of Libra, the Moon would always face the Earth with the same side as in the image on the left (a bird's-eye view from above the Moon's axis of rotation and not drawn to scale). If the Moon had no rotation, as it orbited the Earth, as shown on the right, its front and back would alternately face the Earth.