Why do celestial bodies follow different laws of physics than terrestrial bodies? A non-rotating object has a point on its axis, or axle, continually aligned with a point on the object. An axis is virtual, or imaginary; an axle is real and we live in a real physical world. In a real physical world, there are two ways a non-rotating object can move in a circle: 1. A point on the axle is continually aligned with the direction of motion and a point on the object. This is similar to a horse on a merry-go-round (MGR). The horse is rotating about the center of the MGR, not about its pole. Observer at the center only sees one side of the horse. Distant observer sees all sides of the horse once/orbit. 2. A point on the axle continually faces the same direction and is always aligned with a point on the object. This is similar to a non-rotating wheel on a vertical axle continually facing the same direction while moving in a circle. Observer at the center sees all sides of the wheel once/orbit. Distant observer only sees one side of the wheel. In both scenarios the object is orbiting the center of the circle; not rotating on its axle. In both scenarios, if the object is rotating on its axle and orbiting the center of a circle, a point on the axle is aligned with a point on the object once per orbit. Rotating Object moving in a circle: 1. With the axle moving in the direction of motion and the object rotating once per orbit, the observer at the center sees all sides of the object once. A distant observer sees all sides twice. 2. With the axle continually facing the same direction and the object rotating once per orbit, the observer at the center only sees one side of the object. A distant observer sees all sides once. Now compare tidally locked celestial bodies with a plane flying in a circle, a train moving on a circular track, and a horse on a MGR. Every object's axis is imaginary. None have a real axle about which to rotate. All are orbiting the center of a circle. When the forward motion of the plane, train, or MGR is stopped, the objects are not rotating. Why do tidally locked bodies continue to rotate? Also, in the real world, it's impossible to fit the non-rotating plane, train, or horse into the scenario with an axis always facing the same direction. This can only be done virtually in your imagination.