Tracking data confirms central bearing behaviour

Saturn was tracked for 1.25 hours from (az,el) = (248,58) to (260,41). Despite CfA seeing monitor reports of seeing of about 1" or greater, the 32 elevation pointing residuals showed an rms of only 1.1". That for the azimuth residuals was 1.7", but the impact of the glitch at azimuth 256 is clear :

By comparison with the original data upon which the empirical correction was based, there is little evidence for any change; the peak of this profile appears this time at azimuth 256.0, whereas in the earlier figure it was perhaps 255.8, while the position of the trough is about 256.8 compared with 257.2, earlier. This gives a mean position of 256.4 c.f. 256.5 originally. (All this assumes modest azimuth corrections for the time lag between the mid-point of the pointing measurement and that at which each datum is logged).

The full amplitude is 7", which, being at an elevation of 46.7 degrees, implies a full amplitude at the horizon of 10.2" - compared with the original estimate of 11.2" and the 970409 estimate of 9.8".

Although we have been unable this time to confirm the periodicity of the problem, the details of this one `glitch' suggest that the characteristics of the problem are as they were previously.

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imc 970712