Figure 6. The squares show the telescope defocus data from August 15 (Figure 5) plotted as a function of time. For the defocus data the y-axis is in units of µm. The circles show the telescope altitude in degrees as a function of time.

As expected from the good linear correlation seen in Figure 5, the data very much look like they are driven by altitude changes. This would be the natural explanation for these data accept for two other observations. First, if the data obtained on August 14 were plotted on the same scale, you would hardly notice the variation in altitude seen at that time. The August14 data would appear as a nearly horizontal line on this graph and are completely incompatible with the variations seen here. This is also true of the data taken on April 14! Second, notice that the defocus data consists of pairs of points which were taken at nearly the same telescope altitude. Altitude changes cannot explain why the second points in the first three data pairs drop with respect to the first measurement in each pair. The first six data points make it look as if the altitude change is temporal in nature rather than driven by altitude changes in the telescope. If this is true, then the strong correlation with altitude seen in Figure 5 is simply an unfortunate and very confusing coincidence! I present evidence later in this report supporting this idea.