# Rotation of Heavenly Bodies

by jtban
Tags: bodies, heavenly, rotation
Mentor
P: 11,618
 Quote by jtban Sorry if I wasn't clear. For the horse to move around the oval track and continually face the same direction, is a real problem. The horse is not stationary.
Oh, I thought we were talking about the merry go round.

 An example of an axis always facing the direction of circular motion would be a point on the pole of a MGR horse always facing the forward motion of the MGR.
A point on the pole is not the axis itself. The axis remains perpendicular to the direction the object is moving in its orbit. Remember that the axis is a 1d line and cannot have a direction along any dimension but the 1 it is in. For example, a standard Y axis is aligned vertically and has no other facing in any other direction.
P: 10
 On a Ferris Wheel, the cars revolve about the center axis without rorating.
Thanks for the example. I wish I thought of it.

Keep in mind that an axis is an imaginary axle.

The ferris wheel cars are mounted on axles (axis) that are physically attached (through bearings) to a central axle (axis). Each car is rotating about its axis once per orbit (thank God). All the cars are rotating about the central axis. Also, a point on each axle is continually facing the same direction; not the direction of motion.

Distant observer only sees one side of the cars; the observer at the center all sides once.

This scenario is only possible with the cars mounted on real axles.

Convention would classify the cars as non-rotating celestial bodies.
 Mentor P: 11,618 Jtban, have you been listening to anything going on in this thread? Looking at your latest post, it doesn't look like you've learned anything since we started. I don't mind helping you, but I feel like I keep correcting the exact same errors.
 P: 10 An axis can be imaginary or real. A real axis is an axle. A point on an axle continually faces the direction of motion of the object to which it is physically attached, like the axle of a car on a ferris wheel. The axle rotates with the object to which it is physically attached. The car rotates independently on bearings and always faces the same direction. An object moving in a circle has 2 virtual axes: the stationary center of the circle and the center of the orbiting object. Since an axis is imaginary, a point on the axis can be imagined to: 1) always face the same direction, or, to 2) always face the direction of motion. With the former 1), a non-rotating object orbiting the center of a circle and one rotating twice per orbit are indistinguishable. The center sees all sides of the object once per orbit; distant observer sees all sides twice. The latter 2) view doesn't have this anomaly. It just occurred to me while experimenting that a non-rotating object moving in a circle on an axis always pointing in the same direction is impossible. I couldn't duplicate it. A non-rotating object always looked like one rotating twice per orbit, either pro-grade or retrograde. When researching the subject I became confused because I ran across a blog stating that a non-rotating object is theoretically possible, but that there were no known celestial occurrences. Now I understand why. Took me a while to get to the obvious. Thanks for putting up with me.

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