Dear Jack,

If you have a look at the photo, you get a good indication of where the north celestial pole is by just observing all of those small arcs.

Each night of the year, if we point the camera at the same point, say 'A', in the sky as the camera is pointed at in the photo (centre of the image, but not labelled), 23h 56m 4s later than the previous night's image was started, then the star trails will be exactly the same. I.e., displaying rotation about the north celestial pole, not about 'A'. (The only restriction is that we will need to commence our experiment in the middle of the night such that this 4 minutes per day does not prevent us from getting a good nighttime exposure.)

Now assume that 'A' is in fact the north ecliptic pole and you will see the problem for the heliocentric model.

The north and south ecliptic poles rotate each night about the celestial polar axis, just like any other points on the celestial sphere do.

Regards,

Neville.

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