Great Comets
ATLAS OF THE UNIVERSE
I
t is not surprising that ancient peoples were alarmed
whenever a brilliant comet appeared. These so-called
‘hairy stars’ were regarded as unlucky; remember
Shakespeare’s lines in Julius Caesar– ‘When beggars
die, there are no comets seen; the heavens themselves
blaze forth the death of princes.’ There have been various
comet panics, one of which was sparked off in 1736 by
no less a person than the Rev. William Whiston, who
succeeded Newton as Lucasian Professor of Mathematics
at Cambridge. Mainly on religious grounds, Whiston pre-
dicted that the world would be brought to an end by a
collision with a comet on 16 October of that year, and
the alarm in London was so great that the Archbishop of
Canterbury felt bound to issue a public disclaimer!
If the Earth were struck by a cometary nucleus a few
kilometres in diameter there would undoubtedly be wide-
spread damage, but the chances are very slight. A theory
of a different type has been proposed in recent years by Sir
Fred Hoyle and Chandra Wickramasinghe, who believe
that comets can deposit viruses in the upper air and cause
epidemics such as smallpox. It must be said, however, that
these ideas have met with practically no support either
from astronomers or from medical experts.
Great comets have been rare during the present century,
but many have been seen in the past. For example, de
Chéseaux Comet of 1744 developed multiple tails, and a
contemporary drawing of it has been likened to a Japanese
fan. Even more impressive was the comet of 1811, dis-
covered by the French astronomer Honoré Flaugergues.The coma was 2 million kilometres (1.2 million miles)
across, and the 16-million-kilometre (10-million-mile) tail
stretched out to over 90 degrees, while the tail of the
Great Comet of 1843 extended to 330 million kilometres
(205 million miles), considerably greater than the distance
between the Sun and Mars. It is not easy to remember that
these huge bodies are so flimsy, and that their masses are
absolutely negligible by planetary standards.
Donati’s Comet of 1858 is said to have been the most
beautiful ever seen, with its brilliant head, straight ion
tail and curved dust-tail. Three years later came Tebbutt’s
Comet, discovered by an Australian amateur, which came
within 2 million kilometres (1.2 million miles) of the Earth;
we may even have passed through the tip of the tail,
though nothing unusual was reported apart from a slight,
unconfirmed yellowish tinge over the sky.
The Great Southern Comet of 1882 was bright enough
to cast shadows, and to remain visible even when the Sun
was above the horizon. This was the first comet to be
properly photographed. Sir David Gill, at the Cape of
Good Hope, obtained an excellent picture of it, and this
led to an important development. Gill’s picture showed
so many stars that he realized that the best way to map
the stellar sky was by photographic methods rather than
by laborious visual measurement. The 1882 comet was a
member of the Kreutz Sun-grazing group, distinguished by
very small perihelion distance.
The Daylight Comet of 1910 appeared a few weeks
before Halley’s, and was decidedly the brighter of the two. Comet Arend–Roland,
1957, as photographed by
E. M. Lindsay from Armagh,
Northern Ireland. This comet
will never return; it has been
perturbed into an open orbit. The Great Comet of
1811,discovered by
Honoré Flaugergues. This
impression shows the
comet on 15 October,
from Otterbourne Hill,
near Winchester in England. The Daylight Comet of
1910,Lowell Observatory.
27 January. (Many people
who claim to remember
Halley’s Comet in 1910
actually saw the Daylight
Comet, which was
considerably brighter!)D108-151 UNIVERSE UK 2003CB 7/4/03 5:18 pm Page 142