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Particle Physics and Astronomy Research Council
Royal Greenwich Observatory
Special Information Leaflet No. 16: 'Comet C/1995 O1 Hale-Bopp'
The brightness of Comet Hale-Bopp
Predicting the future brightness of a comet is very difficult because comets are notorious for showing sudden changes in brightness as the surface layers crack open and sublime under the influence of the Sun. However, they do show some orderly behaviour as can be seen in Figure 1.
This shows the heliocentric brightness of Hale-Bopp plotted against the logarithm of the distance of the comet from the Sun. The heliocentric brightness is the brightness of the comet corrected for its changing distance from the Earth. The data points, all converted to heliocentric magnitudes, are taken from visual observations published in IAU Circulars.
We have taken the two straight lines that best fit the points in Figure 1, corrected them for the varying distance of the comet from the Earth to give the curve in Figure 2, which predicts the future brightness of Hale-Bopp. We have also plotted the original observations in Figure 2, using filled symbols, to show how they fit the curve.
These plots were made by Geoff Busswell and Robin Catchpole and predict the comet will reach 0.6 magnitude at the end of March.
How good is their prediction?
The open circles are observations reported in IAU Circulars since their work. Judge for yourself.
Produced by the Information Services Department of the Royal Greenwich Observatory.
MJP, 1997 February 11.
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Updated: February 28 '97, June 23 '14
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