Stefan Kürti´s Astro Web

SOHO comets hunter

Celestial wonders captured his attention in his childhood and he dreamed of being professional astronomer. When he had realized that earning his living with science would be very hard, he prefered teacher´s career. He had built his own telescope as a pupil, but as late as the age of internet, he could fulfill his dream to catch a comet. He searched for a bright comet on evening sky as a small boy, but he failed. Then 44 years has passed until he found his first one. And soon he added more, one by one. Rainer Kracht, hunter of SOHO comets.

Bremen is not only the place where the Bremen town musicians were heading according to the fairy tale, but where you grown up and started to learn about astronomy. How did you get involved with astronomy?

One evening in November 1961 my brother asked me if I would accompany him to the Olbers Society, where an introduction into astronomy should start. I did. They have a small observatory on the roof of the nautical school in Bremen. The lessons were taught by teachers of this school and by a student of astronomy. There is also a small planetarium with a library and of course there were many interesting people. One of them had built one telescope after the other. After one year I started to grind and polish my first mirror and then built my first telescope. It was a Newton telescope with a 15 cm mirror. This was a very exciting time with the Echo satellites in the night sky, the images of Mariner 4 from Mars and my first images of a total lunar eclipse taken with my new telescope.

I made my first astronomical photographs through a telescope in 1964. Among them were images of the total lunar eclipses of June 24/25 and December 19. Some of them were published in a local newspaper. My father worked for them as journalist, so I knew were to go to show my images.

Your passion for astronomy started during your school years. Did you think about being a professional astronomer?

Yes, I wanted to be a professional astronomer then. But I was told that it would be nearly impossible to get a job as such. I think this was true in 1965/1966.

So then you decided for a less romantic profession, you became a teacher. What was your subject as a teacher?

I have been a teacher of mathematics, physics and computer science at Kooperative Gesamtschule in Elmshorn, small town 35 km north from Hamburg. Now I enjoy my retirement.

You became well-known approximately 10 years ago with your first SOHO comet findings. But your really first comet hunt happened many years earlier. How do you remember to that?

I was just nine years old when comet Arend-Roland appeared in the evening sky. My father tried to show me this comet but I couldn't spot it. There is a monument in Bremen for a Roland which saved the city (long ago). I did know the monument and the story about it, perhaps I thought that Arend-Roland must be similar to that monument.

You are the best SOHO comet hunter with 247 discoveries. How did you learn about this possibility of search?

I read an article in Sky & Telescope in October 2000 (Hunting for SOHO Comets Using the Internet). But my internet connection was not fast enough to download many images. The next year I got a faster internet connection and started to search for SOHO comets during the long summer holidays.

Can you recall your first SOHO comet discovery?

I started my search in August 2001 on images taken by C2 coronograph, not knowing much about SOHO comets. But I had studied the images of past SOHO comets so I knew what they looked like. Late on August 21 I found a small moving object in LASCO C2 images. When I had five consecutive images, I sent my first report. It was confirmed by other SOHO hunters, but it took two weeks until the comet was confirmed officially as comet C/2001 Q7. It was one of the rare non-Kreutz comets so they spent a lot of time considering it. Several months later I realized that my first SOHO comet was a member of the new Kracht group of SOHO comets.

There were more than 1850 SOHO comets discovered, most of them belonged to the Kreutz comet group. Except those, comet hunters catched from time to time few non group comets too. Maik Meyer recognized new group in 2002 and later there were added another 3 comet families. Two latter bear your name: Kracht and Kracht 2. You started your hunt from real time images, later you began to check archival data. And thanks to older images you found out both new groups. How was it with Kracht comet families?

I started my archival search on 2002 Feb 06 and found my first comet only after two days. Maik Meyer almost immediately suggested from its apparent motion, that this comet could be a member of his proposed comet group. This turned out to be true. The Meyer group and another one, Marsden group, were officially announced on Feb 18, 2002.

On Feb 27, 2002 I found a non group comet C/1999 M3 in SOHO-images of Jun 30, 1999 I compared its apparent motion with other one non-group comet C/2000 O3 with similar path. In March I found third comet C/1999 N6, having also similar orbit. Later I noticed that the apparent track of my first SOHO comet C/2001 Q7 was close to the track of C/1999 M3. I wrote about this to Maik the next day. He confirmed that C/2001 Q7 could have an orbit between C/1999 M3 and C/2000 O3. Maik gave me some useful hints on how to derive an orbit and I could find a new orbit for my first comet. I computed the new orbit, which Brian Marsden accepted and wrote "Indeed, we could say that these four comets belong to the Kracht group". And up to date this group expanded to 37 members.

The second Kracht group is quite small. In August 2002 I noticed that two non group comets have similar orbits, first of it was found in 1999, second in 2002 August. In a year time, in September 2003 another non group comet appeared with resambling orbit. I suggested that they could belong to a group. And they did. So was the Kracht 2 family identified, presently has 4 members.

Two milestones in Soho comet search are connected with your name - you found 500th, 900th comet, you are also the leader in number of discoveries, but what is your most esteemed result?

This was the linkage of the three non group comets C/2001 D1 = 2004 X7 = 2008 S2 and the discovery of a new set of observations for C/2001 D1 along the new orbit followed by the detection of small nongravitational forces using additional observations from 1997.

How could you manage your SOHO hunt with your duties at school? I think it was hard to search through images and in the morning go to school and teach?

German teachers were paid quite good in the past. I could easily reduce my duties by getting less money. And I could do a much better job with less pupils. I got both: more satisfaction with my job and more time for comets.

It requires an eagle eyes and some experience too to discover sungrazing comets. I think it is quite difficult to catch one and be first to report it! I never succeded. How many time do you use to search SOHO images?

I don't have any records on that. Something between nothing and several hours per day. Nowadays I spend more time with orbital computations, trying linkages, computing nongravitational forces, observing asteroids remotely over the internet, searching for new members of the Machholz Complex in the MPC database, investigating the orbital evolution of small bodies.

After your success with your hunt via internet, haven´t you thought about joining visual discoverers as David Levy, Don Machholz or recently Murakami and Honda?

Of course I thought, but Northern Germany is not well suited for this task - and the morning hours are not my time. But if there is visible one, I observe it. Latest was 103P with 10 x 50 binocular.

Last year you started to search for precovery positions of newly found asteroids in NEAT images. What was the reason of your skip from comets to asteroid world?

I wanted to find a new asteroid. I started with precoveries of main belters and soon found a new one. Sometimes Rob Matson helped me with this work.

Only one month later you made a logical step further and start to observe remotely from the night sky. Did you find the SkyMoprh hunting less rewarding?

I exchanged some mails about asteroid 2009 UV18 (which is in a cometlike orbit) with Rob Matson and asked him if he had ever tried to image such an object with a remotely controlled telescope. He answered that he used Sierra Stars Observatory (G68) in California. I found that G68 is well suited to find new asteroids on my own images.

You discovered 26 minor planets, 16 from SkyMorph archive, 10 from night sky in a period of one year. One of your remotely discovered asteroid was not only numbered, but has been already named. It happened in a really short time, it usually takes 5 or even more years. Did you choose your name proposal only after it was being numbered, or did you decided it well ahead?

I decided well ahead that my first numbered asteroid should be named after my mother (which is now 91 years old and still interested in all things which the family members do). Under the old rules there was a cascade of identifications and I could supply two more oppositions with Skymorph. So it was numbered and named rather soon as 233967 = Vierkant.

Some amateur astronomers plan trips to destinations which are interesting from astonomical point of view. Have you ever been somewhere on such a trip?

I visited the ESO headquarters near Munich many years ago.

Do you want to visit some of well known big observatories?

Perhaps the Very Large Telescope of European Southern Observatory at Cerro Paranal, Chile.

What is your favourite astronomy book ?

There are many. Perhaps the most impressive was "The new Mars", published by NASA about the discoveries of Mariner 9. And one of my first books about astronomy was written by Otto Struve, published in 1962 with only 12 pages about comets, but with magnificent images of P/Halley and comet Arend-Roland (1957). Perhaps this gave me the driving force to search for comets ...

I read somewhere that spacecraft SOHO will ends its mission in near future. Do you know about it?

No, there is no intention to end the SOHO mission. SOHO LASCO may deliver images for many additional years. It's the funding for cometary work (astrometry) which may run out in April 2011.

It means that there is still time for those who want to hunt for SOHO comets? What would you advice them?

It's quite simple during May/June and November/December. Look at the last Kreutz comet and try to find a similar one.

What is your favourite activity these days - to search for another new SOHO comet, hunt from NEAT archival data or quest for new night sky objects?

My favourite activity is always to find something new. New night sky objects are now difficult to find. SOHO (and STEREO) comets are much easier and until now the only way to extend our knowledge of the Machholz Complex.

Finally I wonder whether you still have a dream regarding your astronomy work?

Of course I have, I would like to discover Comet Kracht.

Instead of an epilogue

Rainer still enjoys astronomy. His SOHO comet discoveries stopped at number 255 in the year 2011. He broke off his comet hunt from spacecraft imagery and joined the Teide Observatory Asteroid Survey (TOTAS) program. There as a member of amateur astronomers group he searches for new objects on images from 1-meter telescope on Tenerife, Canary Islands. TOTAS is funded by the European Space Agency ESA. Soon after kickoff, Rainer caught the new near-Earth asteroid 2011 SF108, the first NEO discovered by this survey.

Email communication between SOHO comet hunters has brought Rainer to co-authorship on scientific articles. It began with a study of the Kreutz group of comets along with other astronomers: Quanzhi Ye, Man-To Hui and Paul Wiegert. Rainer has gained recognition among professionals by identifying the SOHO comets groups Kracht 1 and Kracht 2. Expert on dynamics of comets, Zdeněk Sekanina from USA contacted him with his paper "The Origin of the Comet Marsden and Kracht". Communication eventually resulted in cooperation on several professional articles.

In the year 2017 Rainer returned to SOHO comets hunting. Karl Battams, principal investigator of the NASA-funded Sungrazer Project, asked him to do so. Battams greatly appreciated Rainer´s ability to identify nongroups comets. Those comets are mostly overlooked by other hunters. Since then he added some more finds. Today, 270 SOHO comets are on his discovery list.