Objects rotate relative to the box we put them in.
If you paint an arrow on an orange, and sit it in the middle of a mat, the orange is not rotating WRT the mat, because the arrow doesn't change direction wrt the mat.
If I pick up that Orange, hold it at arms length, and start spinning on the spot, then the orange is spinning WRT the mat, because the orientation of the arrow painted on the orange is changing WRT the mat.
If we tie a string to the orange, and I stand there, swinging the orange around my head, after painting an arrow on it, and I happen to be standing facing the same direction as another arrow, painted on a mat, than the orange is still rotating wrt me, because sometimes the arrow on the orange is paralell to the arrow shaved into my head, and sometimes it's anti paralell.
So all that argument goes to prove is how wrong people claiming the moon doesn't spin are.
In the case of the earth-moon system, if we define a meridian, and give that meridian a direction, and paint the lines in place on the earth and the moon, than sometimes the meridians will be aligned paralell, sometimes they will be aligned anti paralell.
Therefore using ONLY THE EARTH AND MOON we can determine that the moon must be rotating as it orbits the earth.
If you paint an arrow on an orange, and sit it in the middle of a mat, the orange is not rotating WRT the mat, because the arrow doesn't change direction wrt the mat.
If I pick up that Orange, hold it at arms length, and start spinning on the spot, then the orange is spinning WRT the mat, because the orientation of the arrow painted on the orange is changing WRT the mat.
If we tie a string to the orange, and I stand there, swinging the orange around my head, after painting an arrow on it, and I happen to be standing facing the same direction as another arrow, painted on a mat, than the orange is still rotating wrt me, because sometimes the arrow on the orange is paralell to the arrow shaved into my head, and sometimes it's anti paralell.
So all that argument goes to prove is how wrong people claiming the moon doesn't spin are.
In the case of the earth-moon system, if we define a meridian, and give that meridian a direction, and paint the lines in place on the earth and the moon, than sometimes the meridians will be aligned paralell, sometimes they will be aligned anti paralell.
Therefore using ONLY THE EARTH AND MOON we can determine that the moon must be rotating as it orbits the earth.