Cosmology

Why does Earth’s moon has same rotation and revolution period ?

Earth has only one natural satellite which revolves around “barycentre” of Earth-Moon system . But you will  amaze to know that Earth’s moon has same rotation and revolution period .It takes about 27.32  days to revolve around Earth and also  it takes same days to make rotation on its axis . That is why , moon always shows one   face  towards Earth . So we can’t see other face of moon. Such coincidence of rotational and revolution period of moon might exist billions year ago when  it was young .   No one knows exact reason but planetary scientists try to explain it in different way .

 

According to them , billions years ago , when moon was young , it was nearer to Earth than today . It used to rotate faster but Earth’s tidal force tried to stretch moon’s geometry gradually  since it was nearer to Earth . Farther point of moon experienced  lesser force than nearer point of moon . It made “bulge” at  moon that was nearer to Earth . This was result that moon  became “egg-shaped” in geometry and that distortion was caused by   experiencing unevenly Earth’s tidal  force over its mass . It was   great impact of Earth’s gravity on the bulge point of moon that was nearer to Earth so when it try to rotate , it feels earth’s gravity ( torque at tip of bulge part)  which resists  rotation  until its rotation period synchronizes with its revolution period . It is called ” tidally locked ”  . Since at this equilibrium , resistance of Earth’s gravity on rotation would be very less.

Vice versa is also true . Moon’s tidal force also affects Earth’s geometry and slows the Earth’s rotation . Therefore , period of day on Earth is increasing at rate of thousand part of second every year .That’s why it is not perceptible .

Do all moons in solar system have same their rotation and revolution period ? 

That is amazing to know that , not only Earth’s moon but all moons in solar system have same rotation and revolution period . They are at same equilibrium . For instance , moons of Jupiter like Ganymede , Europa , Io , Thebe etc . always keep their one half face towards Jupiter . Their rotation and revolution period are coincidence . This is because geometry of moons play a important role in slowing down their rotation . There is exception also . Hypersion , moon of Saturn don’t have such equilibrium .

I am science enthusiast and I love to write blogs for students and youths who love science. I have deep interest in astronomy and cosmology. I believe that science is most effective tool to serve humankind. .