Catch a Star 2002

EUROPEAN EDUCATIONAL PROJECT
"CATCH A STAR"
Project: Comet 153/P Ikeya-Zhang

Contents:
1. Introduction
2. Discovery
3. Historical information
4. Nowadays-orbital elements
5. In the future- prognosis for future observations
6. The Nature of the Comet : Characterization of the comet
7. How did scientists receive the information
8. We make a picture of the comet
· Visual Observations of the comet
· CCD observstions of the comet
· Pictures of the comet from Internet
9.Exercises: Creation of a simple model of the comet using CCD and visual observations
· Determination of the size of the coma and the length of the comet's tail using our CCD observations
· Determination of the size of the comet's nucleus using the values of its visual brightness
10. Comparison of the comet with the bright comet Halley
11. Conclusion

1. Introduction
Comets are the most impressive objects in the Solar system. They, together with
asteroids and meteors, belong to the group of small bodies in the Solar system. Bright
comets on the night sky are one of the most beautiful and holding the breath pictures
made by nature!
In this project we will make a portrait of an extremely beautiful and bright comet- the
comet Ikeya - Zhang.

2. Discovery
This comet was discovered on the evening sky by three amateur
astronomers on 2002 February 1.
Kaoru Ikeya from Japan found the comet on February 1.41, while
using a 25-cm reflector. He described it as magnitude 9.0, with a
weak condensed coma about 2 arcmin in diameter. About an hour
and a half later, Daqing Zhang from China independently discovered
the comet while using a 20-cm reflector. He described the comet as
magnitude 8.5 and about 3 arcmin across.
Paulo M. Raymundo (Salvador, Brazil) found the comet on February 1.91, while using his 25-cm reflector. He described it as about magnitude 7.5 with a coma 5 arcmin across. The comet was named after its co-discoverers.

3. Historical information
Astronomers and amateur astronomers made very active observations of the comet. The observations gave possibility to comet astronomers to calculate the comet's orbit. Using the first observations made by the Japanese astronomer Syuichi Nakano and B. G. Marsden form Central Bureau for Astronomical Telegrams the orbital elements of the comet were estimated and the astronomers supposed that the comet had already been observed in 1532 as comet C/1532 R1. But with the increase of new observations that were sent in the Central Bureau for Astronomical Telegrams new and more accurate orbit elements that showed that C/2002 C1 was more likely related to C/1661 C1 were received. Nakano obtained essentially the same numbers when additional positions from 2002 were added on February 25, although the fit was improved. The result in orbital period for C/2002 C1 was then determined as 365.45 years. On the same date, S.Nakano computed an orbit using only the positions from 2002 and obtained a. period of 367.44 years. B.Marsden released his revised orbit on February 26. Using 309 positions spanning the period of February 1 to 24, he determined the period as 367.17 years. Nakano had a new linked solution forcing the identification of C/2002 Cl (Ikeya-Zhang) with C/1661 Cl (Hevelius). Nakano specified the elements at epochs in 2002 and 1661. Integrating the 2002 set back to 1661 gives a difference of 0.12 days in the time of perihelion passage when compared with Nakano's 1661 set. Integrating both sets backwards gave an estimate of the likely uncertainties involved and we now get the sequence:
1661 Jan 28.9 (+-0.1d); 1273 Apr 25 (+-1.5d);
879 Jan 10 (+-15 d);426 May (+- 500 d)
Continuing observations during February an improved orbit determination, indicating a probable link with the comet C/1661 C1, observed by the Polish astronomer Johannes Hevelius was received. With a period of 300-400 years, the orbit stretched to 100 times the distance of the Earth to the Sun. If the suggested link, which was first suggested by Nakano and Brian Marsden, 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 indicated that it would then have had a previous perihelion passage in 1273 and another around 877.

Fig.3 Picture of comet
C/1661,C1 from
S. Lubienietzki(1667)
Theatrum Comticum Vol.II
( Historia Cometarum,1666),
Amsterdam, The Netherlands

The comet was observed and drawn by Hevelius. Integrations of Nakano's previous linked solution also gave a perihelion in 1273 Apr/May and Muraoka gave 1273 May 26 for his integration of Nakano's previous solution.
But Penk Yoke gave in his catalogue a comet of bluish-white colour and with the appearance of loose cotton that appeared in 1273 April. The details given (movement through Auriga towards U.Maj) mimic the expected appearance of the object for 1273 - the agreement can be improved by having a perihelion passage ~ 20- 30 days earlier than the integrations (i.e. around 1273 April 1, near to Muraoka's result).
Thus it seemed that the 1273 April comet mentioned in the Oriental annals can be equated with Ikeya-Zhang (2002) = Hevelius (1661) and as such could be used refine the long-term integration uncertainties.

4. Nowadays-orbital elements

Fig. 5 Orbit of the comet

To be able we to image how a comet moves in the Solar system, we should know its orbital elements. Some of the orbital elements show the shape and the size of the orbit, other show its position in space while third show over which orbit the comet is found at a definite moment. Calculation of orbital elements is made on the base of a huge quantity of astrometrical observations of the comet. From 1513 observations 1661-2002 M.Marsden has calculated the following orbit elements of the comet C/2002 C1 (Ikeya-Zhang). The comet is a periodical one and that's why it has number 153 and it is written as 153P/Ikeya-Zhang!

Orbital Elements of 153P/Ikeya-Zhang
The orbital elements are taken from MPC 46101. We will show some of them that will give us a notion about the comet's orbit.

153P/Ikeya-Zhang
Epoch 2002 Mar. 27.0 TT = JDT 2452360.5
T 2002 Mar. 18.9799 TT
q 0.507069
Node 93.3703
e 0.990062
Incl. 28.1207

The comet was closest to the Sun, 76 million kilometers (47 million miles, or about half of the Sun-Earth distance) on March 18th. It came nearest to Earth, 60 million km (38 million miles away), on April 30th.
From these orbital elements we can understand that the comet was closest to the Sun at a distance of 0.507076 AU and this means that it was between Mercury's and Venus' orbits. From the eccentricity we can understand that the comet had an elliptical orbit that was near to a parabola. The declination of the comet's orbit to the elliptical plane is only 28.1207 degrees. It is smaller than 90 degrees and this means that the comet and the Earth had one and the same direction of turning round the Sun. The period of the comet's turning around the Sun was 367.17 years.

5. In the future- prognosis for future observations
When we know the period of the comet we can estimate that the next appearance of the comet will be in 2 369's. It has already passed near the Sun 5 times (during 426, 879, 1273, 1661 and 2002 year) so we can suppose that the comet lost huge quantities of its mass. The next time when it will pass near the Earth it can be so bright and impressive for the earth observers only if it doesn't undergo changes in its orbit. But most likely after 367 years (the period of the comet) it will be possible a spacecraft to pass near it and look at its coma and the eruption of nucleus' dist and gas that forms a beautiful and very long tail. In future most likely the comet Ikeya-Zhang will have a smaller nucleus. But if it passes near one of the giant planets, the comet's nucleus can be destroyed as it happened with the comet Shoemaker-Levy.

6. The Nature of the Comet
Characterization of the comet: inner and outer portrait of the comet
(chemical composition, nucleus, coma and tail)
The comet Ikeya-Zhang displayed its beautiful coma and tails. The comet could be seen with naked eyes on March and April 2002. Reaching its maximum brightness (visual magnitude of 3) at the end of March, it has been the brightest comet since the comet Hale-Bopp in 1997.
The comet Ikeya-Zhang closest approach to the Sun occurred
on March 18,at a distance of 0.507 AU (1 AU = 150 million
kilometers). It came near the Earth, on April 29, at a distance of
0.405 AU. These close approaches, as well as abundant
productions of dust and gas from its nucleus, were the reasons
for its unusual brightness. With a revolution period of 367 years,
comet Ikeya-Zhang visited us 4 times.
Immediately after its discovery, astronomers carried out a number
of experiments in order to study dust and gases that were released
by the comet Ikeya-Zhang's nucleus. On the many pictures that we found in
INTERNET the comet had a long blue-white coloured plasma tail. This comet didn't form 2 tails- a plasma and a dust one as, for example, happened with the comet Hale-Bopp. But we know that the nearer to the Sun comets go the more dust and gas is ejected from them. On one of the first photos that were made in March it could be seen many short tails that go out from the comet. We suppose that these are huge streams of gas that came from different cracks in the comet's nucleus. Using our visual observations we calculated that the nucleus of the comet was around 20 km in diameter. This means that the comet didn't have a huge nucleus. For example, the Halley comet had a nucleus with size 8x16 km.
Using our CCD observations we calculated that when the comet passed the perihelion, the coma had size of 19 376km and the length of the tail was 994 901 km.
Many interesting observations were made by astronomers
from different observatories and from the European spacecraft
Odin as well. Comets indeed provide valuable information about
the origin and the formation of the Solar System. Mainly made
of water (for 80%), cometary ices contain various other
molecules that are relics of the primitive nebula at the epoch of
formation of planetesimals. Our present knowledge of comets
suggests that many of these molecules were produced in the
primordial interstellar cloud, before its collapse gave birth to
the Solar System.
Since comets are variable objects, measurements of the chemical composition,
based on observation of species in the comet atmosphere, must be referred to
the water production rate from the nucleus. Water in the Universe cannot be easily observed from the ground, because of the water in the terrestrial atmosphere, which absorbs radiation from space. Most often, the water production rate in comets is deduced from observation of the OH radical. The OH radical is produced by the dissociation of the water molecule by solar UV radiation. The observation of OH lines at 18 cm were made with the Nancay radio telescope.
The strong activity of comet Ikeya Zhang and its close approach to Earth allowed scientists to carry out more challenging observations. Thus, the isotopic variety H218O was searched for and finally successfully detected.
The H218O line spectrum, at 547.7 GHz, was detected in comet Ikeya-Zhang after 45 hours of Odin observations and an effective integration time, on the comet, of 28 hours. The line was observed in parallel by using two of the four sub-millimetre receivers, centred at 549 and 555 GHz and tuned at the line frequency. The receiver outputs were connected to the high resolution spectrometers and to the acousto-optical spectrometer. The integrated signal was, as expected, very weak (0.24 K km/s). The successful detection demonstrated the excellent capability of the Odin instrumentation, regarding the receiver sensitivity and stability, as well as the spacecraft pointing accuracy.
Italian astronomers reported the sodium distribution in the coma of comet C/2002 Cl on Apr. 20.17 UT, using the 3.5-m TNG. Two long-slit spectra showed cometary sodium emissions clearly visible due to the comet's geocentric velocity of -8.3 km/s.

7.How did scientists receive the information:
Scientists received the information from visual, photographical, CCD, photometric and spectral observations and through space apparatuses.
To receive information about this comet many astronomers - professional and amateur- observed the comet with telescopes and CCD. They made a lot of visual, photographical, CCD, spectral and photometrical observations. These observations helped astronomers to make a good picture of the comet.
The orbital elements of the comet were estimated from astrometric observations. Thanks to the photometric observations it could be made a rough model of the comet, taking into consideration the size of its coma, tail and nucleus. The spectral observations and the space satellite Odin helped astronomers to determine the chemical composition of the comet. Earth and space observations gave comet astronomers information for creation of a real and correct portrait of the comet Ikeya-Zhang.

8. We make a picture of the comet:
Visual, photographical and CCD observations made by the group
Visual Observations of the comet:
The group started observing the comet before the beginning of the programme "Catch a Star". We are members of the Bulgaria comet group and that's why we show visual observations of the comet from the period April - May when the comet was very bright.
In the visual observations we used the Methods for amateur observations created by Daniel Green, editor of International Comet Quarterly.
In the visual observations we gave valuation of the visual magnitude of the comet and of the comet's nucleus, valuation of the size of the comet's nucleus and the length of the tail. In the valuation we used Morris' method, in which the brightness of the comet is compared with near stars - standards. It was made and a drawing of the comet. We estimated the size of the nucleus and the tail in arc minutes when we compared the comet with a definite distance between the stars.
In the table we show: the time in UT when the observations were made; the method for determination of the observed magnitude- here M is the method of Moris, Total-the total magnitude, the length of the tail in degrees, degree of condensation from, the size of the coma in minutes, the instruments used for the observation (in this case a binocular with aperture 50mm and magnification 10 mm).

Visual observations made by Nadezhda Lyubomirova:

CCD observstions of the comet
CCD observations were made by Veselka Radeva and Georgi Dzhartov with 50/70 cm Schmidt telescope+ST8 in NAO-Rozhen during the summer astroschool "Catch a Star".
Our CCD gallery: Now we have more than 50 images of the comet that we observed in May and June 2002. We show only 4 of our images from different dates.

Fig 8: Comet 153/P Ikeya-Zhang
14.05.2002. Time:19:57:52
exp=120sec R filter

Pictures of the comet from Internet
Gallery of the best photographes of the comet in Internet!
The pictures from the gallery were selected by Elena Stateva!
The photos are made by one of the best comet photographers Michael Jager. There are pictures made by APOD as well
Fig12 Fig13

Fig14 Fig15

Only for teachers and students that are interested in astronomy and
for whom the observations are exciting and interesting:

9. Exercises: Creation of a simple model of the comet using CCD and visual observations
The main aim of the exercise is to be shown students how huge comets are: the size of the coma, the approximate size of the nucleus and the length of the tail can be determined.
Introduction:
Comets are impressive objects and are appropriate for observation and doing different astronomical tasks.
Necessary information: To calculated the following tasks students have to use their CCD observations of the comet ( or to find CCD observations of the comet in Internet, for example on http://encke.jpl.nasa.gov ) and to give visual estimation of the brightness of the comet's nucleus (or to find such estimations). Students will use the ephemerid MPC of the comet..
Exercise 1:Determination of the size of the coma and the length of the comet's tail using our CCD observations

Fig.16

Task1: Determine the scale of the observation, taking into consideration that the size of the field is 28.05x18.07 arc minutes and 1530x1020 pixels
Answer: 1pixel=1.1 arcsec
Task2 : Calculate the size of the coma and the tail in pixels
Answer: V coma=25.3px Vtail=1299px
Task3: Convert your measurements of the coma and the tail into degrees
Answer : Vcoma=0.0077 arc degrees Vtail = 0.3969 arc degrees
Task4: Applying the well known tangens formula :

Use the fact that during these exposures, the comet was 0.96 Astronomical Units far from the Earth.
Now you may find the diameter of the coma and the tail of Comet Ikeya-Zhang.
Diameter of the coma = 0.96AU x 1495978701km x tg 0.0077 = 19 376km
The tail size = 0.96AU x 149597871km x tg 0.3969 = 994 901 km
If we compare the size of the coma with the diameter of the Earth we will see that the coma is larger than our planet (diameter = 12 600 km).
You can see that this comet's coma is huge, compared with planet Earth:
(diameter = 12 600 km).
Coma of comets is usually 20 000 - 200 000 km across.
If we compare the coma and the size of the tail with Hale-Bopp's coma and tail, we will see that they are not very large. This is because in this case we calculate the size of the coma and the tail in the period when the comet had already passed through the perihelion and started moving away from the Sun.
Compared with the historical record - the comet of 1811 - the coma had diameter of
1 800 000 km.
The tail's size of Hale Bopp is huge as well, 100 million km - to be compared with the 1811 record of 160 million km.

Exercise:2. Determination of the size of the comet's nucleus using the values of the visual brightness of comet nucleus
Task1: Estimation of a value of the nucleus brightness using the Methods for comet observations created by Daniel Green or determination of the brightness of the nucleus from a database for visual observations.
Task2: Determine the absolute magnitude of the comet's nucleus using the formula: A comet's brightness variation with respect to its distance from the Sun is often represented by a "power-law" formula:
observed magnitude = absolute magnitude + 5 log (delta) + 2.5 n log (r)
where delta is the Earth-comet (geocentric) distance in astronomical units (AU), r is the Sun-comet (heliocentric) distance in AU and n is the "power-law exponent." One AU is equal to the Earth-Sun distance - about 93 million miles or 150 million kilometers. In this equation:
m = M + 5 log d + 6.7 log r
This formula is analogical to the formula for estimation of the absolute magnitude. Here the particular thing is that we have one photometrical constant- the coefficient in front
of r. Here this value is estimated on the base of the huge number of visual observations made by amateur comet observers from the Comet section of the British Astronomical Association.
In this formula m is the observed magnitude of the comet's nucleus, M is the searched absolute magnitude of the comet's nucleus, d is the distance between the comet and Earth, and r is the distance between the Sun and the comet.
We gave valuation of the brightness of the comet's nucleus on 4 May 2002 m = 2.5
On this date the comet was at a distance of 0.417 AU from the Earth and on 1.154AU from the Sun.
We substitute in the formula and get:
2.5 = M + 5 log 0.417 + 6.7 log 1.154
M = 3.98
Task3:
To determine the neucleus diameter we will use L.Kresak' formula:
Log D = 2.1 - 0.2 M km,
We estimated that D = 20 km
This result is approximate and is based only on one observation of the brightness of the comet's nucleus. But when we know that the Halley's nucleus had size 8 x 16 km, we think that our result shows that the comet Ikeya-Zhang has a nucleus that can be compared with the Halley's one. Such estimation of the size of comets' nuclei shows that nuclei of comets with short period are much smaller (from 3 to 5 km) than the nuclei of comets with long period. This can be explained with the smaller number of destructive passages around the Sun.

Conclusion: These 2 exercises give a good notion about the size of the nucleus (about 20 km) that a coma with average size ( 19 376 km) and a long tail(994 901 km) has. In this case it is very useful that student can make visual and CCD observations themselves, work the observations up alone and make an approximate model of the comet.

10. Comparison of the comet with the bright comet Halley
To compare the comets we made a picture of both comets- Ikeya Zhang and Halley

Portraits of comet Ikeya-Zhang and the comet Halley:

Both comets had a long period and have passed near the Sun several times. Both comets had approximately the same perihelion distance and eccentricity. But the comet Halley went round the Sun in direction opposite of the Earth's, while Ikeya-Zhang and the Earth had the same directions of going around the Sun. Both comets had approximately the same size of the nuclei. The Halley comet is a typical comet with long period while Ikeya-Zhang had a long period of going around the Sun and that's why it lost less mass of its substance. From the photos of the comets it could be seen that comets developed approximately the same in type tails.

11. Conclusion
The work over the project 'Comet 153P/Ikeya-Zhang' was very interesting and exciting. We found many books, in which we read a lot about comets; we saw many web-pages for this comet.
For us it was very interesting to learn how the comet moves and what the nature of the comet is. We learned to observe comets- visual and with a telescope and to make simple comet models from our observations.
We think that the visual and CCD observations of the comet and creation of this comet's astrofile gave us new knowledge and we learned how we can use our observations to create a model of a distant but a very beautiful comet!

References :
Rendezvous with comets, Nikola Nikolov, Valeri Golev, V. Racheva
The Comet's taile, Newsletter of the Comet Section of the Britush Atsronomical Association, Volume 9,¹ 1,2002 April
The Comet's taile, Newsletter of the Comet Section of the Britush Atsronomical Association, Volume 9,¹ 2,2002 Oktober
http://cfa-www.harvard.edu/iau/info/Astrometry.html
http://cfa-www.harvard.edu/iau/mpc.html
http://cfa-www.harvard.edu/icq/icq.html
http://encke.jpl.nasa.gov/
http://cfa-www.harvard.edu/icq/CometMags.html
http://cfa-www.harvard.edu/icq/cometobs.html
http://cfa-www.harvard.edu/iau/Ephemerides/Comets/index.html
http://cfa-www.harvard.edu/iau/Ephemerides/Comets/0153P.html

For contacts:
GROUP:
Nadezhda Lyubomirova nadezhdaradeva@yahoo.com,
Elena Stateva
Georgi Dzhartov gdjartov@yahoo.com
Leader: Veselka Radeva - Astronomical observatory-Varna, Bulgaria
radevi@mail.varna.techno-link.com
The students are from the Astronomical courses made by the Astronomical Observatory and Planetarium "N.Kopernicus"-Varna