1Can Comet Hunters Survive?
Toshimi Taki and Shigeki Murakami
1. Introduction
Since the Charles Messier’s era, visual comet hunting has been a fascinating field for amateur
astronomers. Dedicated comet hunters win honor and feel a sense of achievement for comet
discoveries. However, in the late 1990s, automated sky survey programs for Near Earth Objects(NEOs) started routine operations and discovering many comets as well as asteroids (Sky &Telescope, December 2000, p. 32). The amateur comet discovery seemed to decline since then.

Especially, the situation looked serious in the northern hemisphere; many comet seekers stopped
hunting in Japan discouraged by NEOs in those days. One of the authors, Murakami, also quitted
hunting once. However, he resumed it with a large aperture telescope and luckily enough he could
find a new comet, C/2002 E2 Snyder-Murakami.

Incredibly, five comets were visually discovered in the northern hemisphere in that year, 2002. On
the contrary, in the same year a new kind of shock was given by Masayuki Suzuki's discovery ofcomet C/2002 O6 SWAN from the SWAN (Solar Wind ANisotropies) images which are open to the
public on the web site. Most comet observers thought faint comets could be found in SWAN images
before amateur comet hunters' discovery.

Among serious Japanese comet observers, there were hot discussions whether comet hunting cansurvive or not under the threats of NEOs and SWAN.

Is it rarely accidental occurrence that five comets were visually discovered in 2002?
Can you actually detect all the comets from the SWAN images that could be visually discoverable?
What would have become of the future visual discovery?

To answer those questions we conducted an objective evaluation on comet discoveries. This study
owes much to the discussions we had with Japanese amateurs.
2. Threat of SWAN
Syogo Utsunomiya, the most successful comet hunter in recent years, emailed one of the authors
Murakami in October 2002; “I am worried myself about Masayuki Suzuki's discovery of comet
C/2002 O6 SWAN from the SWAN images. Can we comet hunters survive?”

Utsunomiya was dismayed to read the Japanese astronomical magazines which said that all the2comets brighter than some 11th magnitude would be found by SWAN. However, he thought faintercomets could be still detectable visually using a large aperture telescope like Murakami’s, though
Utsunomiya’s 15 cm binocular was too small for this purpose. Utsunomiya could not standuneasiness any more and consulted Murakami about usage of large aperture.

Murakami did not worry much about SWAN because few comets were discovered by SWAN before
the finding of C/2002 O6 SWAN. However, he was anxious about it after receiving the email anddecided to inspect the SWAN images to confirm if the visually discovered comets could have been
detected prior to the actual discoveries.

SWAN image of Comet 153P Ikeya-Zhang. Two weeks before the discovery

The result was unexpected: only one comet, 153P Ikeya-Zhang, out of six visually discovered in2001 and 2002 could be discoverable from the SWAN images by his eye. One reason is that the
SWAN images were not open to the public at the time of the discovery and/or a new comet was near
the Sun and out of SWAN’s coverage. Another is much more fundamental: many Japanese comet
observers claimed that they could catch pre-discovered comet pictures on the SWAN images because
they knew the position of the comets. These images are very faint and dim, looks like stain or ghost,and therefore you cannot detect them unless you know the positions. To observe a known comet is
one thing and to find a new comet is another. This holds true whatever you use; a picture, a CCD, theSWAN images and visual observation.

Murakami concluded “no need to worry about SWAN” and emailed this result to Utsunomiya. He
replied, “Your analysis is a great comfort to me. Some people might say, ‘Oh! You still continue tocomet hunt? You are a living fossil.’ It is true that the chance of discovering a new comet may have
reduced but you cannot claim that it is impossible. I will go on comet seeking relying on my eyes
and instrument.”

3. Threat of NEO Sky Survey
We evaluated the threat of NEO sky surveys in two ways, actual comet discovery statistics andsimulation of comet discovery. The simulation enables us to study each element which affects thecomet discovery.

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3.1 Analysis of Actual Comet Discovery
The analysis here is based on the data in Tenmon Nenkan (Astronomical Almanac) publishedannually by Seibundo-Shinkosha, Tokyo, Japan. Tenmon Nenkan lists dates of discovery, orbital
elements and magnitude at discovery for all the new comets found in the previous year. Comet
discovery data from November 1986 to December 2002 are studied below. Comets with very long
period and parabolic/hyperbolic orbit (eccentricity > 0.93) are studied.

The first figure shows trend of discovery. From 1998, discovery of comets with larger perihelion
distance increased abruptly. This corresponds to full operation of LINEAR (Lincoln Near EarthAsteroid Research) project. The trend began in early 1996 when NEAT (Near-Earth Asteroid
Tracking) program began to full operation. Thus, we can identify two periods, “Before NEO Sky
Survey” and “After NEO Survey”. “Before NEO Survey” ended in December 1995 and “After NEO
Sky Survey” started from March 1998. From January 1996 to February 1998 is a transition period.

The second figure shows a comparison of comet discovery per year between the two periods. The
difference is very clear. Professional comet discovery increased 6 times and visual comet discovery
by amateurs in the northern hemisphere decreased to half after NEO sky survey. Amateur discovery
from southern hemisphere does not decrease though.

image from satellite
12perihelion distance, q (AU)10photographic/CCD discovery by professional
NEAT Project

photographic/CCD discovery by amateur
visual discovery by amateur (southern hemisphere)

LINEAR Projectvisual discovery by amateur (northern hemishphere)

8

6

4

2

0
1986/1/1

1988/1/1

1990/1/1

1992/1/1

1994/1/1

1996/1/1

1998/1/1

discovery date

Comet discovery trend

2000/1/1

2002/1/1

2004/1/1

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25
Before NEO Sky Survey(from November 1986 to December 1995)

After NEO Sky Survey(from March 1998 to December 2002)

comet discovery per year

20

19.0

15

10

5

3.2

2.8

1.4
0.5

0.5

0.8

0.0

0.2

0.2

0
amateur,visual,northern

amateur,visual,southern

amateur, professional
photo/CCD

satellite

amateur,visual,northern

amateur,visual,southern

amateur, professional
photo/CCD including
NEO skysurveysatellite

Comet discovery statistics for “Before NEO Sky Survey” and “After NEO Sky Survey”
This figure does not include discoveries by SOHO (Solar Observation and Heliospheric
Observatory) satellite except by SWAN which is one of the instruments boarded on SOHO.

Position of each comet at its discovery was calculated using the orbital element and the discovery
time. Further analysis reveals more interesting facts.
Absolute Magnitude Distribution
Absolute magnitude of comet is defined in the following equation.

m = H 10 + 5 log 10 ∆ + 10 log10 r
where,
m: Magnitude of comet
H10: Absolute magnitude∆: Distance of comet from the Earthr: Distance of comet from the Sun
Absolute magnitude of each comet was calculated from the comet magnitude and its position at thediscovery. The relationship between absolute magnitude and perihelion distance are shown in the
figures below for both before and after NEO survey. Amateur visual discovery is limited to thecomets with small perihelion distance, q < 2. NEO sky survey extends the limiting perihelion
distance further. It is interesting that there is no amateur comet discovery brighter than 6.0 in
absolute magnitude after NEO survey, though the number of samples is not enough. We will discuss
this trend later using simulation.

5

photographic/CCD discovery by professional
10photographic/CCD discovery by amateur
visual discovery by amateur (southern hemisphere)
visual discovery by amateur (northern hemisphere)

perihelion distance, q (AU)

8

6

4

2

0
-4

-2

0

2

4

6

8

10

12

14

16

18

absolute magnitude, H10from November 1986 to December 1995

Absolute magnitude and perihelion distance plot for “Before NEO Sky Survey”

image from satellite
photographic/CCD discovery by professional
photographic/CCD discovery by amateur
visual discovery by amateur (southern hemisphere)
visual discovery by amateur (northern hemisphere)

10

perihelion distance, q (AU)

8

6

4

2

0
-4

-2

0

2

4

6

8

10

12

14

16

18

absolute magnitude, H10from March 1998 to December 2002

Absolute magnitude and perihelion distance plot for “After NEO Sky Survey”

Comet Position at Discovery
Comet positions at discovery are plotted in the figures below. The positions are expressed in ecliptic
coordinates and longitude difference between comet and the Sun. A line of elongation of 80-degeee
is also plotted in the figures. Visual discovery before NEO sky survey mostly occurred in the region
within 80-degree elongation. On the contrary, almost all the professional discovery occurred in the

6region beyond 80-degree elongation. Tsutomu Seki, the co-discoverer of the famous Comet
Ikeya-Seki, pointed out that the sky coverage of the automated sky surveys is limited beyond
80-degree from the Sun and there is a good chance to discover comets visually in the sky near theSun.

Note that discovery in the morning sky is more than discovery in the evening sky.

photographic/CCD discovery by professional
photographic/CCD discovery by amateur
visual discovery by amateur (southern hemisphere)
evening sky

morning sky

visual discovery by amateur (northern hemisphere)90
80 degree
elongation

latitude (degree)

60

30

0

-30

-60

-90
-180

-150

-120

-90

-60

-30

0

30

60

90

120

150

180

∆longitude from the Sun (degree)
Comet Position at Discovery -- from November 1986 to December 1995

Comet position at discovery for “Before NEO Sky Survey”

image from satellite
photographic/CCD discovery by professional
photographic/CCD discovery by amateur
visual discovery by amateur (southern hemisphere)
visual discovery by amateur (northern hemisphere)

evening sky

morning sky
90

latitude (degree)

60

30

0

-30

-60
80 degree
elongation
-90
-180

-150

-120

-90

-60

-30

0

30

60

90

120

150

∆longitude from the Sun (degree)
Comet Position at Discovery -- from March 1998 to December 2002

Comet position at discovery for “After NEO Sky Survey”

180

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3.2 Simulation of Comet Discovery
This is a comet hunting competition in a computer. Who is the first discoverer of the comet that is
randomly generated in the computer, amateur comet hunters or NEO sky surveys? The author (Taki)
was an enthusiastic reader of Scientific American column “Computer Recreations” by A. K
Dewdney in the 1980s. The column inspired him to perform the simulation.

Monte-Carlo method is used in the analysis. 3,000 virtual comets are generated in a computer. Visual
comet hunters in the northern and the southern hemispheres and NEO sky survey in northernhemisphere are also assumed in a computer. Calculation is performed to find when the comets
become bright enough to be discovered by them. Effect of atmospheric absorption is considered in
the analysis.
Assumptions(1) Distribution of Comets
Comets with parabolic orbits are assumed in the simulation. Distributions of the orbital elements are
assumed as follows.
lTime of passage in perihelion distributes uniformly in 25 years, from 2003 to 2027. This
assumption was put in order to consider the effect of the position of the Moon and the Sun.

l

Perihelion distance distributes uniformly from 0 astronomical unit (AU) to 10 AU.

lLongitude of ascending node and argument of the perihelion distribute uniformly from
0-degree to 360-degree.

l

Triangular distribution is assumed for inclination, no comets at 0-degree and 180-degree andthe peak of the distribution is at 90-degree. This distribution is derived from the same comet
discovery data described above.

Distribution of absolute magnitude H10 of comet is assumed to be a normal distribution with meanvalue of 11.0 and standard deviation of 4.0. The distribution is based on detailed analysis of thecomet discovery data.
(2) Amateur Comet Huntersl

Sky Coverage¨

Lower limit of altitude at the beginning or the end of twilight: 5 degree¨

The Moon should be below horizon when illumination fraction k is greater than 0.2.

llLocation¨

Comet hunter in the northern hemisphere: Longitude 0 degree, Latitude 35 degree North¨

Comet hunter in the southern hemisphere: Longitude 0 degree, Latitude 35 degree South
Limit Magnitude: 10.0 and 12.0 are considered.

8(3) NEO Sky Surveyl

Sky Coverage of LINEAR Program

We consider LINEAR is a major threat to amateur comet hunters because the sky coverage of
LINEAR is the widest in the NEO sky surveys. Analyzing the sky coverage plots published in
LINEAR program and the Minor Planet Center home pages, the author derived the sky coverage
pattern of LINEAR as follows.

¨

LINEAR observes declination from -30 to +80 degree.

¨In near full moon period (illuminated fraction, k >= 0.9), LINEAR does not work.

¨

For 0.9 > k > 0.8, LINEAR observes declination from +60 to +80 degree.

¨

Limitation of right ascension is limited by altitude at the beginning or the end of twilight asfollows.

h = 25 o sin( 2(δ + 10 o )) + 45 owhere,
h: altitude
δ: declinationlLocation: Longitude 106-degree East, Latitude 32-degree NorthlLimit Magnitude: 18.0

Result of Simulation
The result of the simulation is plotted in the figures as the same manner as the actual comet
discovery data. In the figures, the simulation assumes limiting magnitude of amateur discovery 10.0.
Readers will be surprised with the resemblance between the simulation and the actual data. All theobservation made for the actual discovery data are consistent with the result of the simulation. A big
difference is that the actual discovery by amateurs in the southern hemisphere is much fewer thanthat in the simulation. This means that amateur comet hunters in the southern hemisphere have been
missing the chance of comet discovery.

After NEO survey period the number of comets visually discoverable with the absolute magnitude
brighter than 8 reduces in the northern hemisphere. This trend, the reduction of bright comet
discovery on the basis of absolute magnitude in the northern hemisphere, corresponds to the actual
one as mentioned above.

The explanation of this finding is as follows. The comets with brighter absolute magnitude enter thecoverage of the NEO surveys when they are far away from the Sun and not bright enough for theamateur comet hunters’ reach. Some of the comets with fainter absolute magnitude and small
perihelion distance increase brightness up to the limiting magnitude for the amateur comet hunters,

9when they approach the Sun without entering the coverage of the NEO surveys. The plot of
discovery position for after NEO sky survey obtained by the simulation suggests where to search.
visual (southern hemisphere)

10

visual (northern hemisphere)

perihelion distance, q (AU)

8

6

4

2

0
-4

-2

0

2

4

6

8

10

12

14

16

18

absolute magnitude, H10
Simulation -- before NEO Sky Survey

Absolute magnitude and perihelion distance plot for “Before NEO Sky Survey” by simulation –visual limit magnitude 10.0

NEO sky survey

10visual (southern hemisphere)
visual (northern hemisphere)

perihelion distance, q (AU)

8

6

4

2

0
-4

-2

0

2

4

6

8

10

12

14

16

18

absolute magnitude, H10

Simulation -- after NEO Sky Survey

Absolute magnitude and perihelion distance plot for “After NEO Sky Survey” by simulation – visual
limit magnitude 10.0

10visual (southern hemisphere)
evening sky

morning sky

visual (northern hemisphere)90
80 degree
elongation

latitude (degree)

60

30

0

-30

-60

-90
-180

-150

-120

-90

-60

-30

0

30

60

90

120

150

180

∆longitude from the Sun (degree)
Simulation -- before NEO Sky Survey

Comet position at discovery for “Before NEO Sky Survey” by simulation – visual limit magnitude
10.0
NEO sky survey
visual (southern hemisphere)
80 degree
elongation

evening sky

morning sky

visual (northern hemisphere)

90

latitude (degree)

60

30

0

-30

-60

-90
-180

-150

-120

-90

-60

-30

0

30

60

90

120

150

180

∆longitude from the Sun (degree)
Simulation -- after NEO Sky Survey

Comet position at discovery for “After NEO Sky Survey” by simulation – visual limit magnitude
10.0

The figure below shows comet discovery rate per year obtained from the simulation. The comet
discovery rate of NEO sky survey is assumed to be the same value as the actual data, 19.0. Again,
the simulation is consistent with the actual data except for the discovery rate of amateur comethunters in the southern hemisphere. Amateur discovery rate from the northern hemisphere after NEO
sky survey becomes one third of before NEO sky survey. The impact of NEO survey to amateur
comet hunters in southern hemisphere is much less.

In the both hemispheres, if you make the limiting magnitude of your telescope darker from 10 to 12,

11

it would give rise to the chance of discovery by 50%. While this requires 2.5 times larger aperture
telescope and the same applies to the low magnification, which narrows the actual field of view.
Thus, your search area per unit time is to be reduced and you do not know whether the large apertureis effective or not. It seems that there is no royal telescope for comet hunting.

30
Before NEO Sky Survey

After NEO Sky Survey

comet discovery per year

25

NEP sky survey
discovery up tomagnitude 18.0
19.0

20

15

visual discovery up
to magnitude 10.0

visual discovery up
to magnitude 12.0

visual discovery up
to magnitude 10.0

visual discovery up
to magnitude 12.0

10
5.0
5

3.3

5.2

3.0
0.9

1.5

1.5

amateur,visual,northern

amateur,visual,southern

amateur,visual,northern

2.60amateur,visual,northern

amateur,visual,southern

amateur,visual,northern

amateur,visual,southern

amateur,visual,southern

NEO skysurveyComet discovery rate comparison by simulation

Competition and Cooperation for Near Earth Comet Discovery
The following two figures show how severe the competition is.
500 near earth comets with perihelion distance smaller than 1.0 are considered here. The square withblack solid line shows numbers of comets which can be discovered by the NEO sky survey ifamateur comet hunters do not work. The square with blue solid line shows numbers of comets which
can be discovered by the amateur comet hunters in the northern hemisphere if the amateurs in thesouthern hemisphere and the NEO sky survey do not operate. The square with red solid line shows
numbers of comets which can be discovered by the amateur comet hunters in the southernhemisphere if the amateurs in the northern hemisphere and the NEO sky survey do not operate.
Number of comets in each block enclosed by solid lines is shown in the figures.

Competition occurs where the squares overlap. Overlap between the NEO sky survey and theamateur comet hunters is large and the NEO sky survey has an advantage over the amateur comethunters in the overlapped area.

The NEO sky survey and the amateur comet hunters can discover 68% to 76% of the near earth
comets (perihelion distance, q<1.0). Most of the undiscovered comets are small ones with faintabsolute magnitude. Note that the NEO sky survey misses many near earth comets. Without theamateur comet hunters, the discovery rate of near earth comets will decrease to 60%. The amateur

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comet hunters compete with the NEO sky survey, and also complement it.
Out of Coverage ofNEO Sky Survey

Visual Comet Hunters inNorthern Hemisphere(Limit Magnitude: 10.0)215 (43%)

6 (1%)

21 (4%)

158 (32%)30(6%)

18 (4%)NEO Sky Survey(Limit Magnitude: 18.0)
296 (59%)

26 (5%)
82(16%)
Visual Comet Hunters inSouthern Hemisphere(Limit Magnitude: 10.0)
223 (45%)

Discovery rate of near earth comets by simulation – visual limit magnitude 10.0

Out of Coverage ofNEO Sky Survey

15 (3%)

44 (9%)

203 (41%)

Visual Comet Hunters inNorthern Hemisphere(Limit Magnitude: 12.0)
292 (58%)

30(6%)
NEO Sky Survey(Limit Magnitude: 18.0)
296 (59%)

27 (5%)
25 (5%)

38(8%)

Visual Comet Hunters inSouthern Hemisphere(Limit Magnitude: 12.0)
299 (60%)

Discovery rate of near earth comets by simulation – visual limit magnitude 12.0

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4. Conclusion
Comet hunters can survive for the time being, though the discovery rate reduced to one third in thenorthern hemisphere after NEO sky survey. In the southern hemisphere if the search becomes active
higher discovery rate is expected than the statistics to date.

When Kaoru Ikeya discovered his 6th comet 153P Ikeya-Zhang, 35 years has been past since his last
discovery (Sky & Telescope, July 2002, p.70-73). Shigehisa Fujikawa has spent 24 years to find his
5th comet that named him, C/2002 X5 Kudo-Fujikawa. Both of them continued comet hunting for
decades of years without hesitation. Tsutomu Seki emphasizes importance of self-confidence anddedication; “Strong rivals exist at any era and only comet hunters who fight bravely and attack
openly are crowned with victory”.

Unless complete sky coverage of the NEO sky surveys is realized, amateur comet hunters cansurvive but they have to swim with the sharks. Comet hunting goes on.
5. References[1] “The Searches for Near-Earth Objects,” Sky & Telescope, December 2000, p. 32.
[2] “The Comet Master”, Sky & Telescope, July 2002, p. 70-73.
[3] Jean Meeus, “Astronomical Algorithms,” Willmann-Bell, Inc., 1991.
About the Authors
Toshimi TakiToshimi Taki is an aircraft engineer by profession and he is a member of Oriental Astronomical
Association (OAA), which is the oldest amateur astronomical society in Japan. He is interested in
astronomical computing and telescope making. His articles on mirror cell analysis and a program for
digital setting circle appeared in Sky & Telescope. His e-mail address is zs3t-tk@asahi-net.or.jp.
Shigeki Murakami
Shigeki Murakami is a forest hydrologist and a snow scientist of the Japanese National Institute,
Forestry and Forest Products Research Institute. He is a discoverer of C/2002 E2 Snyder-Murakami
and also a member of OAA. You can contact him at cometsm@nifty.com.