AAO Press Releases
14 January 1998
Comet Hale Bopp's Elegant Neckline
Comet Hale-Bopp, which provided sensational viewing in
the northern hemisphere last year, is again attracting
attention as it recedes from the inner Solar System.
In early January 1998, the Earth passed through the plane
of the comet's orbit (the flat slice of space in which
Hale-Bopp moves). Dust particles ejected from the comet
during its passage around the Sun accumulate in this
plane, suggesting that a thin, flat dust-cloud might be
seen faintly by scattered sunlight as the Earth passes
A group of Italian astronomers, led by Marco Fulle
(Trieste) and Gabriele Cremonese (Padua), predicted the
appearance of a bright line, or spike (Neck-Line) in
addition to Hale-Bopp's normal tail. Observations of the
Neck-Line will provide important data on the comet\rquote
s structure and activity.
The Italian astronomers requested the Anglo-Australian
Observatory to photograph the event using its UK Schmidt
Telescope near Coonabarabran in New South Wales. In
making their request, they pointed out that this was the
only instrument in the world capable of producing the
deep, wide-field images required.
During the first week in January, three wide-angle
photographs of comet Hale-Bopp were obtained. At the
time, the comet's distance was almost 600 million
kilometres. All three photographs show a well-developed
Neck-Line structure, and one of them, taken on the night
of January 2/3, is shown here.
The slender Neck-Line, in reality composed of dust and
small stones, seems to pierce the heart of the comet and
its tail---although most of the material visible in the
Neck-Line actually lies between Earth and the comet.
The three photographs will be sent to Italy for analysis,
and it is expected that they will reveal much about dust
ejection and dust/gas interaction in Comet Hale-Bopp.
These observations have significant implications for our
understanding of comets in general. Images may be viewed