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June 13

Synchronous orbit

I think I understand the different poles (near pole, far pole, leading pole, trailing pole) and associated hemispheres of a body with a synchronous orbit, but I'd like to double-check. I've drawn (badly) a diagram showing my understanding of these things (see right), and I've given a shot at explaining it at Rhea (moon):

Rhea is tidally locked and rotates synchronously; that is, it rotates at the same speed it revolves (orbits), so one hemisphere is always facing towards Saturn. This is called the near pole. Equally, one hemisphere always faces forward, relative to the direction of movement; this is called the leading hemisphere; the other side is the trailing hemisphere, which faces backwards relative to the moon's motion.

Is this right, or am I missing something? Cheers, Cremastra (talk) 21:35, 13 June 2024 (UTC)[reply]

I have the impression some assumptions are missing from the definitions in our articles Poles of astronomical bodies and/or Synchronous rotation. Without additional assumptions, the aspect of the satellite as seen from the body it circles is subject to possibly significant libration. One assumption is that the orbit of the satellite is circular. The other is that its axis of rotation is aligned with the normal to the orbital plane – in other words, its poles of rotation and orbital poles coincide. Under these assumptions, your diagram corresponds with the definitions given. The intersection of the green–yellow band and the red–blue band is a pole of rotation and the three axes defined by the various kinds of pairs of opposite poles are at right angles to each other. --Lambiam 18:35, 14 June 2024 (UTC)[reply]

Because of the curve of the orbit, the line between the true rearmost and forward-most points is inward from the geometric center of the satellite. The article implies that this difference is ignored in practice. —Tamfang (talk) 20:23, 18 June 2024 (UTC)[reply]