| 13 | 13 | We then take the rotation sequence of exposures and perform this analysis for each of them. We now have a sequence of L,M for different rotator positions. If the telescope's knowledge of the rotator position were exactly right, these values should all be the same. If the rotator were rotating about a different location (ie, a different location on the sky than that expected by the telescope), then these positions should follow a circular path with the radius given by the offset between the telescope-expected location of the rotator center on the focal plane and the true location of the rotator center. An offset of the center of this circle (or the zero-radius circle) would imply that the telescope has a different focal plane coordinate as a reference from the psastro analysis. We fit a general ellipse to this measured path. Below are figures showing the path for a series of altitudes. The bottom set of panels in each figure gives the residuals to the elliptical fit. |
