Discovery
Several
observatories in the United States and elsewhere search the sky every
clear, moonless night to look for asteroids which might eventually pose
a threat to Earth; however, with such a systematic search of the sky
come other interesting discoveries as well. S. H. Pravdo, E. F. Helin,
and K. J. Lawrence (Jet Propulsion Laboratory) announced that the 1.2-m
Schmidt telescope at Palomar Observatory (California, USA) had found a
comet on 2001 August 24.40 in the course of the Near Earth Asteroid
Tracking (NEAT) program. The comet was found on CCD images and the
astronomers were able to confirm the discovery on August 26 and 27. The
comet was described as a round nebulosity measuring about 8 arc seconds
across. The total magnitude as given as 20.0. Confirmations also came
from other observatories on August 27 and these indicated a brighter
total magnitude. J. Ticha, M. Tichy, and P. Jelinek (Klet Observatory)
gave the magnitude as 17.8, while P. J. Shelus (McDonald Observatory,
Texas, USA) gave it as 17.3.
Historical
Highlights
This comet was first announced on IAU Circular
No. 7695 (2001 August 28), when Daniel W. E. Green gave the discovery
details, as well as a "very uncertain" orbit by Brian G. Marsden. The
orbit indicated the comet might pass perihelion on 2005 August 25, with
the closest distance to the sun being just over 4 AU. The reason for
the orbit's uncertainty was because the comet was moving very slowly
due to its rather great distance from the sun. Marsden's orbit
indicated the comet was probably over 11 AU from the sun when
discovered. Kazuo Kinoshita published an orbit for this comet on his
website on September 5. This orbit used 25 positions spanning the
period of August 24 to 31 and indicated a perihelion date of 2004 May
23 and a perihelion distance of 0.99 AU. Such an orbit indicated a
potentially bright apparition for this comet, but little excitement was
generated as more observations were needed to firmly establish an
orbit. Confirmation of Kinoshita's calculations came on September 10,
when IAU Circular No. 7711 included new positions, as well as
an orbit by Green which was based on 38 positions from the period of
August 24 to September 10. This orbit indicated a perihelion date of
2004 May 26 and a perihelion distance of 1.00 AU. Green wrote that the
perihelion date "is still uncertain by several weeks, but it appears
that this comet may become an easy binocular (and possibly naked-eye)
object in May-June 2004." As it turned out, the comet was discovered
when 10.1 AU from the sun.
The comet slowly brightened during the
remainder of 2001 and throughout 2002. As 2003 began, the comet was
still fainter than magnitude 15, but it steadily brightened as the year
progressed, reaching 14 near the end of May, 13 early in July, and 12
around mid-September. September of 2003 also marked the time that
amateur astronomers in the Southern Hemisphere began supplying regular
visual observations of this comet. The coma diameter was typically
given as 0.6 to 1.2 arc minutes.
CCD images by amateurs also began showing a short fan-shaped tail
pointing northward in July. By late September, this tail extended about
0.8 arc minutes
toward the northwest. As 2003 came to an end, the comet had become
slightly brighter than magnitude 10, with a coma diameter of about 2
arc minutes. A faint, fan-shaped tail extended about 4 arc minutes
toward the east.
Predictions: The comet should be at
its brightest during the first half of May. The Central Bureau for
Astronomical Telegrams predicts a maximum magnitude of 0.9, although
their brightness parameters have not been updated in many months.
Several experienced amateur astronomers are keeping close tabs on this
comet. Andreas Kammerer (Germany) looked at all available observations
obtained up to the end of November 2003, and suggests the comet's total
magnitude may reach 2. Seiichi Yoshida (Japan) indicated during the
last days of 2003 that the maximum brightness might reach 2.
The comet steadily brightened as the year
progressed. Observers indicated the brightness attained magnitude 8 in
mid-February, 7 in mid-March, 6 as April began and 5 shortly before
mid-April. The coma grew in size during this same period, with
estimates near 2 arc minutes at the beginning of February, 5 arc
minutes
around mid-March, 10 arc minutes as April began, and 15 arc minutes
around mid-April.
The comet finally appeared to amateur
astronomers of the Northern Hemisphere on the night of May 3/4.
Numerous observers in the United States, from Texas, New Mexico,
Arizona, southern California, and Hawaii, were able to spot the comet
at a very low altitude just below the star Epsilon Canis Majoris. Most
observers described the comet as appearing like a globular cluster
between 7 and 10 arc minutes
across, while a few noted a tail extension. Around this same time,
observers in the Southern Hemisphere were giving the magnitude as
between 3.2 and 3.6 on that date. The comet passed closest to Earth on
May 6 and quickly attained a higher attained for northern observers
during the next week. Naked-eye observations were obtained from
dark-sky locations and observers generally noted a magnitude of 2.8 to
3.0. The tail was initially a short stub, but soon became longer and
developed a filamentary structure. In addition, many observers noted
the sunward side of the coma was abnormally bright, and many specially
processed digital images revealed hoods near the nucleus.
|