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why do we only see one side of the moon

Why does the Earth only see one side of the Moon? (I know about sychronous orbit, I'm just asking why)
The Moon rotates exactly once per revolution of the Earth which is the reason why it shows only one face at the Earth. If you face a pole and move around the pole showing your face at the pole all the time, you will notice that you have rotated once per revolution around the pole. Why has this happened to the Moon? It is due to tidal forces of the Earth. You know that the Moon's tidal forces causes the high and low tides on the Earth. In the same way, the Earth exerts tidal forces on the Moon which are more powerful as the Earth is more massive than the Moon.


It turns out that these forces exert torques on the rotating system and tends to slow its rotation till it finally shows the same face towards the other body. Hence, it is the effect of tidal forces of the Earth on the Moon that have caused the Moon to show only one face to the Earth. Similarly, the tidal forces of the Sun on Mercury have slowed down its rotational period to once in 59 days. The Moon's tidal forces will have the same effect on Earth, so that some day in future (billions of years hence), the Earth may show the same face to the Moon.


This page was last updated on July 18, 2015. Since launching in 1990, the has captured some of our corner of the universe, from neighboring planets to distant nebulae. An updated picture released by the European Space Agency shows two galaxies colliding 350 million light-years away, a process the ESA has been tracking for 52 years, reports. Galaxies are constantly changing shape and creeping through space. When two of these massive networks cross paths, their stellar material begins to intermingle, and they eventually merge into one entity under the force of gravity.


In this image depicting two barred spiral galaxies in the Cetus constellation, the two nuclei are still separate, but the explosive merging process has already been set in motion. Long tidal tailsstreams of gas, dust, and starsfeather out from the top of the cluster. The bright blue patches indicate "stellar nurseries" where gas and dust stirred together by gravity are producing new stars. The photograph was first released in 2008, but this latest version has been updated using Hubble's Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3).


According to anPESAP, the galaxies "are like a natural experiment played out on a cosmic scale, and by cataloguing them, astronomers can better understand the physical processes that warp spiral and elliptical galaxies into new shapes. " Galactic mergers are a vital part of the evolution of the universe: Even the Milky Way is on course to crash into a neighboring galaxy 4 billion years down the road. But the process, though violent, is slow-moving. It will be millions of years before these two galaxies in Cetus settle down into one. [h/t ]

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