In the course of my work on the Catalogue of Comet Discoveries an essential part is the investigation of historic records of comet observations. This is very interesting and leads sometimes to surprising findings. Besides libraries the WWW is a major source of my information. There exist now a lot of archives of journals and additional possibilities for recherche. Second-hand bookshops maintain central search engines, too. In March 1999 I found the following entry after entering the keywords "Bruhns" and "Komet" into such a search engine:
"Bruhns, Carl Christian (Astronom, 1830-1881). Eigenh. Brief mit Unterschrift. Leipzig, 30 IX. 1862. 1 Seite. Kl.-8°. "Herrn Generalconsul Clauss ladet zu Sonnabend den 4 Octbr Abends 6 Uhr zu einer Sitzung des Ausschußes der Leipziger Carl Ritter-Stiftung auf der neuen Sternwarte ein ergebenst C. Bruhns für den Vorstand". - Dazu: Bleistiftskizze "Komet" Laut beigefügter zeitgen. Notiz Darstellung von B- vom 9. VII. 1874. - Beide gering fleckig."
Bruhns, Carl Christian (Astronomer, 1830-1881). Autographic letter with signature. Leipzig, 30 IX. 1862. 1 page. Kl.-8°. "Mr consul general Clauss invites for Saturday the 4th of October, evenings at 6 to a meeting of the committee of the Leipzig Carl Ritter Foundation at the new observatory. Sincerely C. Bruhns for the managing commitee. - In addition: Pencil sketch "Comet" According to an attached contemporary note drawn by Bruhns on July 9, 1874. - Both lightly blotched."
My attention awoke suddenly: Was this an authentic sketch of an observed comet that was mentioned here? My catalogue showed three possible comets, C/1874 D1 (Winnecke), C/1874 G1 (Winnecke) and C/1874 H1 (Coggia). The discoveries of these three comets took place in February and April 1874, respectively, so that the time of observation was relatively unusual - except it was a very bright object. A look into Gary Kronks "Comets - A Descriptive Catalog" confirmed only one candidate: C/1874 H1 (Coggia). It passed its perihelion on July 9, 1874, - surprisingly the same date the sketch was made. This in mind I decided to buy the sketch.
At this place some words about Carl Christian Bruhns. He was born on November 22, 1830 in Plön, Germany. Since 1852 he was observer in Berlin and became in 1868 director of the Leipzig Observatory, a construction which he had planned and supervised. He discovered 5 new comets, C/1853 R1, C/1855 V1, C/1858 K1, C/1862 X1, C/1864 Y1 and recovered comet P/1857 F1 (Brorsen). His working field also contained orbital calculations of comets and asteroids. Further observational highlights were the solar eclipses of 1867 and 1868, the transit of Mercury in 1868, distance calculations of the companion of Sirius and phase observations of Venus. After calculating the orbit of a meteor shower of November 27, 1872, he concluded that it originated from comet 3D/Biela. Bruhns died on July 25, 1881, in Leipzig.
Comet C/1874 H1 (Coggia) was discovered as a 7.5m bright object on April 17, 1874, by Coggia in Marseilles (France). After its discovery the comet increased steadily in brightness and showed first details in its coma. The perihelion was reached on July 9, 1874, at a distance of 0.68 AU. At this time the comet was as bright as 1.5m and possessed a tail of 13° length. Bruhns estimated the comet on July 13 with the unaided eye as brighter as Capella (0.2m) under mediocre conditions (low elevation, cirrus). It is not unreasonable to assume that the comet was brighter than 0m! The tail was now 20° long and showed a dark lane. Additional observations showed hoods surrounding the central condensation in solar direction.
On July 18 the comet reached its perigee at a distance of only 0.25 AU and surprisingly the central condensation was no longer visible. The tail increased further and was estimated as long as 65° by Schmidt in Athens (Greece) on July 21. After this the comet moved into the southern sky and was observed until mid-October from there.
After receiving the documents I was at first disappointed of the sketch (fig. 1). It was made with pencil, small (ca. 3 cm x 4 cm) and looked like a very raw sketch. The central condensation is very distinctly visible and the border of the telescope's field of view is hinted. When I started to examinine the sketch more closely I discovered some more details which match the historic descriptions.
Fig. 1: Whole view of the sketch. The text means: "Comet, drawn by Prof. Bruhns
on Thursday the 9th of July 1874 at the Leipzig Observatory."
(Click for a larger version, 1500 x 2148, 423 kB!)
Since July 7 Bruhns spoke of a distinctly visible, dark lane within the tail. This lane is hinted behind the central condensation and may be the shadow of the nucleus. Also around the time of the perihelion Bruhns and other observers described a very conspicuous jet with a high apex angle. On July 9 Bruhns estimated an apex angle of about 140°. In the sketch this is visible above the central condensation. It originates at about 10h and winds to the right until about 2h. As an angle this means 120° - nearly the value of Bruhns.
A further "proof" is the possible depiction of a star. In the tail, right from the tail axis, one can see a small (intentional?) point. After checking with the GUIDE 7.0 software I was able to identify this possible star with PPM 31386 (SAO 26579) which was there in the night from July 9 to 10 and the brightest star (6.7m) within the area of the tail (fig 2). Also, the sketch shows the comet exactly how it would be visible in a telescope at this time. Both facts confirm the date given on the sketch. Of course I can not totally exclude the possiblity of a concidence. Figure 3 shows the sketch with the mentioned details.
Fig. 2: Position of the comet at the time of observation made with GUIDE 7.0
Fig. 3: Indication of identifiying details
Unfortunately I can not judge how to classify this sketch. Was it one of many testing sketches from which a final sketch was drawn later? Or is it a raw sketch maybe for a friend? Unfortunately no verbal descriptions are given on the sketch by Bruhns himself - only a note which was added later (cf. fig. 1). The very lax kind of sketching the field of view and the absence of additional field stars or an indication of north or solar direction speaks for a raw sketch. It is possible that Bruhns used only raw sketches for his later verbal descriptions. Some answers may be found by comparing this sketch with his observational reports in the Astronomische Nachrichten.
I am still amazed how relatively firm the identity with comet C/1874 H1 (Coggia) can be proven. The historic observations match the details of the raw sketch. I will try to compare the sketch with the reports and drawings in the Astronomische Nachrichten. Nevertheless it is very interesting what little and maybe big pearls one can find in second-hand bookshops and possibly flea markets, too.
If you have any questions, please email me (firstname.lastname@example.org).