Phil, I think your confusing the termonology with the geometry......sidreal days are identical in GC or HC. The reasons are different due to the motions. However, in any case no matter what you call it........24 hours from midnight point will be always be midnight again by defiinition of 24 hours. Further, the camera will be in a radial position to the sun(annual axis) we are looking for rotaion around the annual axis. If the rotaion exist, then regaurless of what ever else is happining and the reason why in the universe, the rotation would manifest itself for the same exact reasons it does nightly. we ar in radial rotation about that axis. The mehcanics of Sidreal days are irrelevant and the real cause/mechanics of sidreal days is a point in question. philip madsen <pma15027@xxxxxxxxxxxxxx> wrote: This is no win for HC over GC but, Since Regner caused me to utilize an old word "translation" in a new application, it sure makes these descriptions simpler. Sure enough I have awakened this morning with the certain conviction that there is only one rotation, and only one axis of rotation. I am a little embarrassed it took so much unnecessary mental and written wrangling to arrive. We have already agreed that the 2AU translational movement was far too small relatively to read any effect due to parallax. (i.e.make trails) . For there to be an annual increment or circle, we needed and assumed there to be a spin of the world due to its orbit, in addition to the daily spin. This would only occur if the orbit was liken to a rigid wheel and the globe rotated inside a frame that was fixed solidly on the rim And it isn't. There is no applied force of "rigidity" to insist on it. If it was, then I can see the precessional force due to the daily rotation. It doesn't happen. Therefore we must accept the conclusion that we cannot disprove HC simply because of the absence of an annual star trail. There is no rotational spin element given to the world in its translation around the sun. The only spin is the daily sidereal spin. Lets put it differently. There is no physical reason for this orbital translation to cause a spin. It is necessary to avoid any misconceptions which the geocentric view creates that tends to bias our minds.. Both mathmatically and geometrically it is proven by simple proportion, and it is in accord with what is observed. Lets draw it. Under HC. Fact 1. The planet has a fixed incline to the ecliptic. It always faces the same direction throughout the orbit. Fact 2. It has one revolution/spin per sidereal day. and 366 rotations for a 365 solar day year. Reqd to prove: That geometrically the world does not need to gain spin due to its translation around the sun. For simplicity we will assume that the body "earth" has two sidereal day spins per orbit of the sun. For visualisation. let the object be the typical classroom globe, and start our orbit with the tilted N pole pointing outwards on the enclined axis and the international date line of the globe is at noon pointing at the sun. Keeping the tilt always in the same orientation, move the entire unit 180 degrees around its orbital path, and at the same time rotate the globe one full turn. This is one sidereal day. But note, the date line is now only at midnight. This is not due to any extra spin of the earth, but merely because its "frame" has been translated in position relative to the sun. You have to complete one more complete sideral day whilst returning to the start point to complete a solar day. Note that the same geometrical relationships occur no matter which direction of either rotation ,orbit or spin, is taken. In the real world, one sidereal day or one rotation of the earth is not going to complete a solar day because the orbital translation moved the world to another location relative to the sun. Sorry for the long wind, but I must say in conclusion, the exact same observations would be made if the world was stationary, and the sun and Stars rotated the earth in the same angular proportions. I am grateful for the very good graphic video available in GWW showing the two planetary systems in action.. Philip.