Comet C/2002 C1 Ikeya-Zhang
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Comet Ikeya-Zhang, designated C/2002 C1 (Ikeya-Zhang), is named
after Kaoru Ikeya of Shizuoka prefecture, Japan, and Daqing Zhang of Henan
province, China, who independently discovered it on the night of 1
February 2002. A preliminary orbit reported the following day indicated
that it would come moderately close to both the Earth and the Sun and that
it might become visible to the naked eye during late March and April
By the end of February, observations had shown that the comet was indeed
brightening according to expectations, although its sky position,
relatively close to the Sun, would make it a difficult object to observe.
In addition, it appears to have a fairly high gas-to-dust ratio, reducing
the prominence of the developing dust tail.
Continuing observations during February also allowed an improved orbit
determination, indicating a probable link with the comet C/1661 C1,
observed by the Polish astronomer Johannes Hevelius
. With a period of
300-400 years, the orbit stretches to 100 times the distance of the
Earth from the Sun. If the suggested link, which was first suggested by
the Japanese astronomer Syuichi Nakano and Brian Marsden of the Minor
, is confirmed, then Comet Ikeya-Zhang would have a record
orbital period for a 'periodic' comet (i.e. one recorded as having
returned more than once). Calculations indicate that it would then have
had a previous perihelion passage in 1273 and another around 877.
Figure 1 shows an engraving of the 1661 comet observed by the
mathematician Erhardus Weigelius of Jena.
Figure 1: Engraving showing Comet C1661,C1, from S. Lubienietzki
(1667) Theatrum Cometicum Vol. II (Historia Cometarum,
1666), Amsterdam, The Netherlands. Detail from Diagram No. 77, opposite
Figure 2: View of the orbit of Comet Ikeya-Zhang at discovery on 1
February 2002. At this time, the comet was approximately 170 million km
from the Sun and 230 million km from the Earth. The figure shows the comet
moving in a direction from south to north, reaching its perihelion
position (the point closest to the Sun) on 18 March 2002, and then rising
higher in the northern sky before finally returning south. The comet's
closest position to the Sun is approximately 76 million km; and the
closest approach to the Earth (perigee) is approximately 60 million km.
The latter occurs at the end of April.
The orbit is unusual in passing exceptionally close to the orbit
of Jupiter, enabling close encounters to that planet. At the present time,
Jupiter is well away from its near-intersection point with the comet's
orbit, but the next time the comet returns (in the twenty-fourth century)
it is expected to have a close approach to Jupiter, whose gravity will
substantially perturb the comet's orbit. The possibility of strong
gravitational perturbations by Jupiter during each revolution means that
the dynamical evolution of Ikeya-Zhang is particularly rapid.
Despite its relatively short period (it may be only 341 years since its
last return to the inner solar system), Comet Ikeya-Zhang may have
experienced just a handful of perihelion passages since it was captured
from an initial orbit in the Oort cloud (a nearly spherical swarm of
comets that surrounds the solar system stretching halfway to the nearest
star) with an initial period of revolution measured in millions of years.
The star charts show the path of the comet against the stars
during March, April and May 2002. The horizon has been drawn to show the
view from Northern Ireland at 8.00,p.m. (GMT) on 1 March and
10.00,p.m. (BST) on 1 April respectively, but if you are observing from
another site, or at a slightly different time, the view will be broadly
similar except that the aspect will be slightly different. For example,
the view from London is similar to that shown, except that it occurs about
half an hour earlier.
Figure 3: The path of Comet C/2002 C1 (Ikeya-Zhang) against the fixed
stars is shown during March and April, when it is expected to become
easily visible with binoculars. The constellation positions with respect
to the horizon have been plotted at 8.00,p.m. (GMT) on 1 March 2002.
Figure 4: The path of Comet C/2002 C1 (Ikeya-Zhang) against the fixed
stars is shown during the period April to early May. The constellation
positions with respect to the horizon have been plotted at 10.00,p.m.
(BST) on 1 April 2002.
The comet remains close to the Sun in the sky throughout March, and so
will be located close to the horizon, low in the west to north-west after
dark. During April the comet skims the northern horizon, becoming a
morning object (in the north-east before sunrise) later in the month. The
proximity to the Sun in the sky means that in order to see the comet at
all it will be necessary to have a clear, dark sky with a good view
towards the north-west and northern horizons. A dark sky, far from city
lights or other forms of light pollution, is an absolute necessity in
order to see the full extent of the cometary head and tail.
It is best to have a clear, dark sky to see most astronomical objects,
even more so when they are faint, diffuse objects like comets. It is
important that there are no clouds right down to the horizon, as the view
will be limited if there are any clouds. Check the weather conditions
regularly and take the opportunity when there are clear skies.
The best advice, then, is to take whatever chance the weather provides,
and to make observing Comet Ikeya-Zhang a top priority whenever clear
skies are forecast. It is well worth driving a short distance to avoid
city lights and domestic light pollution. Plan ahead, and take the trouble
to locate a site with a clear view to the west (March), north-west (April)
and north to north-east (late April and May). Allow at least 10-15
minutes for your eyes to become properly dark-adapted, and if you have
access to a pair of binoculars - use them. Binoculars greatly improve
the view compared with the naked eye, and make it easier to `star-hop' to
the comet if it should turn out to be fainter than expected or if there is
mist or cloud near the horizon.
For those with cameras, loading it with a fast film, setting it on a firm
mount and using an exposure of 20 to 30 seconds on full aperture may be
sufficient to record an image of the comet.
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Chronological history of the science and folklore surrounding comets.
BAA Comet Section
Gary Kronk's Cometography Page
IAU Minor Planet Center
Joe Rao's article on Ikeya-Zhang
Paul Gitto's Arcturus Observatory Home Page
The Astronomer Magazine Online
Image of Ikeya-Zhang comet, taken on march 27, at 17:35 UT, from Talmassons Observatory by Rolando LIGUSTRI and Lucio FURLANETTO with 30 cm Newton Telescope, focal length 1750 mm (f/5) and SBIG ST9E CCD. Time of integration: 4 frames of 10 sec each. In this picture you can see that the comet tail is extremely dusty and the gas emission is low.
There are more excellent images
of Ikeya-Zhang on the CAST website.
Astronomy Picture of the Day
Martin Mobberley's Images
1661 Comet (courtesy Jonathan Shanklin)
Last Revised: 2009 November 23rd