Comet C/1907 L2(1907d) Daniel

Daniel Zaccheus Daniel ( * 1874 , † 1964) was an American astronomer . Daniel worked since 1903 together with Henry Norris Russell on Halsted Observatory at Princeton University , where he began observations of variable stars . Already in June 1907 discovered Daniel a bright comet, which dominated the reporting of Scientific American in the summer 1907.

Daniel discovered on 7 December 1909 periodic comets 33P / Daniel and on 1907 the comet 1907d. From 1910 he worked at the Allegheny Observatory of the University of Pittsburgh . Zaccheus Daniel discovered this comet in the morning sky on June 10th,1907, with a 15cm Comet Seeker . The comet was located at R.A 23h 48.6m amd dec, -1 deg 08' in Pisces. He suspected it as being a comet , but due to morning twilight , he was unable to detect any motion. On the 12th, W.R.Brooks, using a 24cm refractor observed it and confirmed it as a comet describing it as, "round with a central condensation and a fainter stellar nucleus".

On June 14th, R.G Aitkin (Lick Observatory,California) said the comet was visible with the aid of a opera glass. On the 16th, E.Hartwig (Bamberg,Germany), observed it with a 25cm refractor and estimated it as m1=9.5 and 2' coma with an observation of m2=10.
On the 17th, C.W.Wirtz (Stasbourg,France), determined the magnitude to be 8.4 with a 6' coma with a nuclear magnitude of 11.
By the 19th, the magnitude was widely reported at 8 with a tail forming and at P.A of 247 deg.
On the 22nd, G.Zappa (Rome college,Italy), estimated the magnitude to have risen to 7 and noted the comet was now sporting a fan-shaped tail extending towards the West.
During July 1907, the comet was approaching both Earth and Sun respectively and on the 2nd, the magnitude was still 7 and the coma appearing 3' in diameter.
On the 15th, E.Silbernagel (Munich,Germany), observed the comet with a 27cm refractor and described it as; "very bright". Magnitude was given as 7 and with a very sharp,prominent nucleus and tail extending out of his scopes F.O.V.
A week later on the 10th of July, the magnitude had risen to 5 with the comet now displaying a 1-1.5 degree tail.
By months end, the comet was brightening fast and attained a magnitude of 3 with a coma 8' being reported and a tail 3 degrees in length.
Perigee came on August 2nd at 0.75 AU and the comet continued to brighten, albeit slowly.
By mid-month it was magnitude 2 and with a 2 degree tail and as August came to a close it was still shinning at magnitude 2 with a diameter of 2' and 3 degree long tail.

Comet photography was still in its infancy , but this comet was the most photographed for its time and images obtained during August showed clusters of 15- 20 rays, which, a short distance from the coma diffused to form the tail. Photographic tail lengths from August showed 17 degrees of length and images obtained on July 11th and August 18th, showed distinct disconnection events . During September , the comet moved into Leo during morning twilight .

Perihelion was on the 4th at 0.51 A.U. The magnitude was given at this time as 1.5 and a nuclear magnitude of 4.5. After this the comet faded and was last glimpsed in strong twilight on the 24th at magnitude 3. The comet then moved into conjunction with the Sun and was to be recovered on November 11th at magnitude 8.5 and with a 1' coma. The comet remained at these values during November , and by mid-December had dropped to magnitude 9, and very diffuse. Observations continued into 1908, and during February, was m1=10. Thereafter , the comet was hard to observe, but the last suspected observation was by Wolf (Heidelberg,Germany) when he spotted a nebulous object near the expected position on plates exposed on April 19th, 1909 at m1=16. These observations have a doubt though as this was at the very limit of the plates capabilities . On this date the comet was r=7.26 AU, Delta=6.33 AU (Libra).

Light curve

Comet Daniel on 20 July 1907 19:50GMT Courtesy of “Historic archive of Catania Observatory”

           

Series of images of the comet from 10 to 13 August 1907 obtained with a 30 inch reflector. Exposure 7min. Courtesy of “Historic archive of Catania Observatory”