8th August 2000: The VLT images the Comet Linear breakup shower
NEWSALERT: Friday, July 28, 2000 @ 1431 GMT
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DEATH OF A COMET: LINEAR BLOWN APART
Astronomers report that Comet LINEAR, the brightest comet of the
year, appears to have blown apart. The comet, which at one time was
predicted to become visible to the naked eye, dramatically faded this
NASA OBSERVATORIES KEEP THEIR 'EYES' ON LINEAR
When NASA's two great observatories, Hubble and Chandra, recently
observed comet LINEAR astronomers received some abrupt surprises.
Researchers were able to catch the icy comet in a brief, violent
outburst when it blew off a piece of its crust, like a cork popping
off a champagne bottle.
Comet LINEAR (C/1999 S4)
for Comet Linear
Comet C/1999 S4 (LINEAR) was discovered on 27 September 1999 by the
Massachusetts Institute of Technology/Lincoln Laboratory
LINEAR (Lincoln Near Earth Asteroid Research), at the White Sands
Missile Range in Socorro, New Mexico, USA. The LINEAR programme
uses a 1m prime-focus Cassegrain telescope to search the sky for
comets and asteroids passing close to the Earth, is funded by the
United States Air Force. Initially, Comet LINEAR was thought to be a
, but observations soon showed that it had an
unusual motion for an asteroid and a diffuse appearance showing both
a coma and tail, typical of a comet.
Comet LINEAR was discovered at a distance of approximately 600 million
kilometres from the Earth (more than four times the distance of the
Earth from the Sun). Predictions of its anticipated brightness as it
approached both the Earth and the Sun indicated that it could become
visible with the naked-eye a few days before and after its closest
approach to the Earth on 23 July at a distance of about 56 million
kilometres (about 1/3 the distance of the Earth from the Sun). The
comet's closest approach to the Sun (perihelion) occurs a few days
later, on 26 July.
It is believed that Comet LINEAR is a first-time visitor to the inner
solar system, having left its `home' in the Oort cloud
, on the
extremities of the solar system, many millions of years ago. The Oort
cloud is a sphere of comets which surrounds the entire solar system
stretching roughly half-way to the nearest star, some 15 to 20 million
million kilometres from the Sun.
The star chart shows the path of the comet toward the northern horizon against the fixed stars as
they will appear around midnight during July. Comet C/1999 S4
(LINEAR) will pass below the blade of the Plough at the time of
maximum brightness between 20 and 27 July. It will also be circumpolar
it will remain above the horizon all night) during most of
In order to see any astronomical object at its best it almost goes
without saying that it is necessary to have a dark, clear sky. This is
especially true for faint, diffuse objects such as comets. Clouds are
astronomers' biggest bug-bear, and unless the sky is clear right down
to the horizon the view is bound to be limited. A dark sky is an
absolute necessity in order to see the faint cometary tail.
The advice is to plan ahead and take the trouble to locate a dark
viewing site with a clear view towards the northern horizon. Then take
whatever opportunity is provided by the weather, whenever there is a
forecast of clear skies!
Comet LINEAR is not expected to be an easy naked-eye object, and
better views will be obtained with binoculars. These should provide a
good view of the cometary head and tail. If the comet is fainter than
expected or if there is mist or thin cloud, binoculars will also allow
you to `star-hop' to the comet using the star chart above.
Finally, allow at least 5-10 minutes for your eyes to become properly
dark adapted. For those with cameras, loading it with a fast film,
setting it on a firm mount and using an exposure of up to about 30
seconds on full aperture may be sufficient to enable this rare visitor
from the Oort cloud to be imaged. After swinging once around the Sun,
Comet LINEAR is not due to return again until 32,000 AD.
Animated Image of Linear
Sky and Telescope
Suggestions for Further Reading
The Armagh Planetarium
(028-3752-4725) has an excellent range of books
on astronomy, and provides a fast mail order service. Details of other
suppliers can be found in astronomy magazines such as Astronomy Now
available from newsagents. The following books, which should be
available from most libraries, give a good introduction to the field.
Bailey, M.E., Clube, S.V.M. and Napier, W.M. The Origin of
Oxford: Pergamon Press, 1990. Comprehensive history
describing all theories of cometary origin and the development
of Man's concerns about the cosmos.
Brandt, J.C. and Chapman, R.D. Rendezvous in Space: The Science
New York: W.H. Freeman & Co., 1992. Popular introduction
to comets and the results of the 1986 apparition of Halley's comet.
Gehrels, T. Hazards due to Comets and Asteroids.
University of Arizona Press, 1994. Comprehensive collection of
articles covering most aspects of comets and their likely interaction
with the Earth.
Kronk, G.W. Cometography: A Catalog of Comets.
University Press, 1999. A descriptive catalogue of every comet which
has been observed throughout history, from ancient times to the end of
the eighteenth century.
Marsden, B.G. IAU Circular
No. 7267, 1 October
1999. Announcement of discovery of Comet LINEAR.
Marsden, B.G. IAU Circular
No. 7383, 17 March 2000.
Predictions for the brightness of Comet LINEAR.
Napier, Bill Nemesis,
Headline Press, 1999. Novel revolving around an impact hazard scenario.
Niven, L. and Pournell, J. Lucifer's Hammer.
Publications, 1978. Classic work of fiction describing a cometary
collision with the Earth.
Olsen, R.J.M. and Pasachoff, J.M. Fire in the Sky.
Cambridge University Press, 1998. Paintings, photographs, drawings and
other works of art concerning comets, meteors and related phenomena,
illustrating the influence of science on art.
Spencer, J.R. and J. Mitton. The Great Comet Crash.
Cambridge: Cambridge University Press, 1995. Illustrated articles
describing the collision of Comet Shoemaker-Levy 9 with Jupiter in
Yeomans, D. Comets.
New York: Wiley Science, 1991.
Detailed chronological history of the science, myth and folklore surrounding
22 June 2000
Last Revised: 2010 February 22nd