Most of northern Europe was clouded out for this rare event but observations
were possible from Dorset after the sky cleared minutes before the observing
window was due to open. A time-series of CCD images was taken +/-4 minutes
centred on the predicted time of the occultation.

My location was nominally 370 km from the centre of the JPL ephemeris track,
but more recent high-precision astrometry based on >550 images (mean
residual 0.09") taken with the two 2.0-m Faulkes Telescopes over 12 years,
analysed by Mike Kretlow of CORA, indicated a shift in the track of some 470
km further northwards which means that the shadow probably missed my
location by ~800 km. N.B. The JPL ephemeris uses approx 24,000 observations
but many reports to the MPC are subject to measurement bias where outbursts
of the comet shift the photocentre away from the apparent position of the
nucleus. The high-precision astrometry avoids use of images taken soon after
such outbursts.

The lightcurve attached shows no significant deviation of >15% on a 2.25-sec
time resolution (=27 km at the comet) that would be indicative of obscuring
matter along the line of sight of the star. A 1-minute moving average shows
no evidence for coma extinction greater than 1.5% in the region down to
about 800 km from the nucleus. The photometry uses weighted-mean zeropoints
based on 4 comparison stars (see attached chart).

Richard Miles
BAA

See also: https://britastro.org/node/25237