The Moon Doctor

I  worked all the way through my lunch break getting stuff ready for a short tripette that I have to make next week. My regular post-prandial blogpost  is consequently a bit later than usual, and also a bit shorter.

Anyway, the little orbital dynamics question I posted a couple of days ago, which seems to have attracted quite a number of responses, also reminded me of something that happened about 12 years ago,  just after I had moved to Nottingham to take up the position of Professor of Astrophysics at the University of Nottingham. I was sitting in my office, working – blogs hadn’t been invented then – when the phone rang and the voice at the other end said May I speak to Professor Coles please? When I replied that I was he, the caller went on to explain that he was a surgeon who worked at Queen’s Medical Centre, a hospital located right next to the University of Nottingham, with teaching staff working for the University.

It turned out that news of the setting up of the new Astronomy group there had made it into the University newsletter which my caller had seen. He asked if I had a few moments to answer a question about astrophysics which had been bothering him for some time and which he had just been discussing with some of his colleagues.  I said yes, and he asked: Does the Moon rotate?

I paused a bit, thinking how best to explain, and he went on to clarify his point, which was that if the Moon always has the same face towards the Earth does that mean it’s not rotating.

Understanding his question, I went on to explain that, yes, the Moon does rotate and that the reason it always shows the same face to the Earth (more-or-less, ignoring libration) is that the period of its rotation is the same as the Moon’s orbital period around the Earth. I also explained how to demonstrate this with two coffee mugs, moving one in a circle around the other and rotating the outer one so as to keep the handle pointing towards the central mug. Moreover, I explained the physics of this phenomenon, which is called tidal locking, and pointed out other examples in astrophysics.

After this spiel the caller said that was all very interesting but he had to go  now. Assuming I had bored him, as I fear I tend to do rather a lot, I apologized for going on about it for too long. He said no he wasn’t at all bored by the detail I had put in, he found it all absolutely fascinating. The reason for him needing to go was that he had to go back to tell the answer to the colleagues he had been discussing it with  just before phoning me.  They were all  in the operating theatre,  standing around a patient lying on the operating table, waiting  for him to return and complete the operation he had left in order to make the call…

10 Responses to “The Moon Doctor”

  1. Rhodri Evans Says:

    Did the patient die due to the length of your explanation? Manslaughter due to verbosity?

  2. Surgical lunacy !

  3. If there were no other celestial bodies other than the Earth and the Moon, what would be the easiest experimental proof that they did rotate?

    • – I mean, that the Moon did? Earth rotation is easy, just get a pendulum…

    • Anton Garrett Says:

      Relative to what, if there were no other celestial bodies?

    • Has anyone ever solved this problem of Mach’s Principle? In other words, if there is only one object in the universe, can one experience a centrifugal force?

      • This is the first thing I’ve read by you. “Moon Doctor” is very likeable…I follow Ken Rice on Twitter and that is how I found your writing. You received two very clever comments about this story. Look forward to reading more of your stories and comments. Brevity is the soul of wit, I am still working on that one. RHIC2011 on Twitter

  4. You know that the motion of bodies in a rotating reference frame is not the same as in a non-rotating one. Witness the fact that the Moon doesn’t accelerate directly towards the Earth and crash into it. Witness the Kerr metric being measurably different from Schwarzschild. And witness Foucault’s pendulum.

    That is the very simplest refutation of the nonsense known as ‘Mach’s Principle’. You can know about rotation without looking higher than the rooftops – distant galaxies have no say at all in the matter.

    Anyway, if one determined the Earth’s rotation sufficiently accurately, the orbital angular speed of the Moon follows by subtraction.

    • Anton Garrett Says:

      “You can know about rotation without looking higher than the rooftops – distant galaxies have no say at all in the matter.”

      Aren’t they what the rotation is relative to?

      • Right, that’s the whole point. Why are centrifugal forces felt only if there is rotation relative to distant parts of the universe? One cannot be sure that “distant galaxies have no say at all in the matter” unless one has done such an experiment.

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