# rotation and revolution.Can anybody make it clear to me what reason lies behind rotation and revolution of a celestial body?

enotechris | Certified Educator

Although these terms may be used interchangeably, in referencing celestial bodies they may have different meanings.  Rotation means a body spinning about its own axis, whereas revolution means a body moving around a central point, or orbiting.  So Earth rotates in 24 hours, and revolves or orbits around the Sun in a year. However, it is still correct to say the Earth revolves in 24 hours and rotates around the Sun in a year.  Better to use the term orbit and minimize confusion!

The cause of these motions is due to how the body was first formed from the swirling gases and debris that moved around the primeval Sun.

astrosonuthird | Student

Rotation means rotating on its own axis and revolution means revolve around something. For ex =  the earth spinning on its own axis and revolving around the sun.

astrosonu | Student

Hello! Sudhansu. These are very simple topics. Rotation means moving round in its own axis and revolution means moving around a point. For eg - Days and nights happens because of the rotation of the earth and the seasons change because of the revolution of the earth.

gracious15 | Student

Rotation means a body spinning about on its own axis, where revolution means a body moving around a central point, or orbiting.  So Earth rotates and revolves or orbits around the Sun .

giorgiana1976 | Student

Movements of celestial bodies in the solar system can be deduced from the laws of motion and the law of universal gravitation. As Kepler showed, all planets are moving in elliptical orbits and the Sun is in one of the outbreaks. We can learn a lot about planetary motion considering the particular case of circular orbits. We neglect the forces between planets, considering only the interaction between the Sun and a given planet.These considerations apply equally well the movement of a satellite (natural or artificial) around a planet.
Two bodies which are moving on circular orbits under the influence of universal mutual attraction.

F=G*m1*m2/r^2

Both bodies have the same angular velocity ω. There are two spherical bodies of masses m and M, moving in circular orbits under the influence of mutual gravitational attraction. Center of mass of this two bodies system is  on the line joining them,in a point C so that: m*r=M*R If there are not external forces that act on this system, the center of mass has no acceleration. In this case,  C is chosen as the origin of reference system.Large body of mass M is moving in an orbit of constant radius R and small body of mass m is moving in an orbit of constant radius r, both bodies having the same angular velocity ω. For this to occur, the gravitational force acting on each body has to ensure the necessary centripetal acceleration. Since the gravitational force is an action-reaction pair, centripetal forces must be equal in absolute value and have an opposite sense. Specific condition is: the gravitational force exerted on each body is equal to the centripetal force needed to keep moving on circular orbit, ie: (G*M*m)/(r+R)^2=m*ω^2*r. If a body has a mass larger than the other, as if the Sun and a planet, its distance from the center of mass is much smaller than the distance of the other body. It is assumed that R is negligible compared to r. Above equation becomes: GM=ω^2*r^3 This is a fundamental equation for planetary motion, it is also valid for elliptical orbits if we define the r as large semiaxis  ellipse. An immediate consequence of the equation is that it predicts Kepler's third law for planetary motion in the particular case of circular orbits.

epollock | Student

Rotation concerns movement on its own axis and revolution means rotation around another object.

neela | Student

I think the answer to this in  lies in the laws of motion  of Newton.

Have you seen  a thrown away stone spins but not stopping the spinnng  in the middle before it reaches earth?

Nothing can move from without external force.Moving things can never stop without external force. The spinning of the plannet is due to its the initial conditions inherited from its mother. It cannot stop movement because there is no external force to stop it. It is free enough and big enough with huge moment of inertia  in space conduct this rotation by conserving its angular momentum.

Revolution is a result of  thrown away from  its mother in an exeeding speed when she herself was spinning. Even we send satellites which revolve around the earth with a determined velocity to go to a predetermined altitude. If you send the satellite spinning it will spin till its end. The revolution is the dynamical play as a resultant gravitational pull and the centrepetal force which is again a result of initial velocity.

Thus both cause of rotation and revolution is due to inherited initial condition and nothing else. Regarding the terminology  it is the language an its freedom. One terminolgy denotes rotation about an internal and the other about the external axis(  through the sun).

krishna-agrawala | Student

Rotation of a celestial body refers to its movement around its own axis. It is a movement like spinning of a top. Revolution of a celestial body refers to its movement around another larger celestial body. For example, Earth and other planets revolve around the Sun, and the Moon revolves around the Earth.

Original celestial bodies like sun were formed by accretion of less dense or rarer material into masses of denser material. During the process of accretion these bodies started rotating due to uneven accretion. This rotation movement increased as these bodies became denser.

The revolution of the celestial bodies is the result of how parts of larger bodies got separated to form smaller bodies. For example, the Earth was formed by separation odd part of the Sun from it, and the Moon was formed by part of Earth separating from it. When these parts separating from the mother body they have a circular motion because of the rotation the mother body. However these separated body are not able to move away from the mother bodies indefinitely due to gravitational force and thus they continue to rotate around them.