Central bearing measurement

The last measurement ( 981115 ), showed the empirical to be overcompensating by about 1".

The latest measurement tracked Uranus, using the SCUBA map16 method, and with the empirical corrections enabled, from (az,el) = (214/45) at 17:22 HST to (230/34) at 18:29 (thanks Jane) :

The del residuals show no baseline trend and have an rms of 0.3" - there is no record of the seeing during this period, but it must be as good as this. Taking account of the baseline trend in daz, the azimuth residuals show about a peak-to-peak error of 5.7" centered at (223.8,39.9). The residual effect at the horizon would then be 7.4" peak-to-peak, in the sense of being an overcompensation by tel_empircial. The current full amplitude of tel_empirical is 14.3" so the current peak-to-peak amplitude of the defect at the horizon is therefore 6.9".

While the location in azimuth is within 0.1 degrees of that expected, the trace above shows considerable broadening of the feature at earlier azimuths - it is (now, here) about 4 degrees wide on the approach.

The new data are added to the historical record .