This comet was discovered in Orion, on November 24th 1915, by the Southafrican Clement Taylor (69P/Taylor = 1915 W1). It was magnitude 10 and moved slowly. Taylor did not communicate his discovery until December 2nd, when the Union Observatory at Johannesburg confirmed the discovery. What is curious is that nobody beat him to the announcement despite the fact that in early December the comet was close to Mintaka (Delta Orionis), the right hand star of Orion’s belt and thus in one of the most intensely observed regions of the sky. However, with most European astronomers more concerned with the war, a large part of all observational astronomy in the world had come to a halt.
During the first week of January the comet reached maximum at magnitude 8.7, coinciding with its closest approach to Earth. Perihelion was passed on January 31st 1916 at 1.56AU. With perihelion interesting things started to happen. On February 10th Edward Emerson Barnard noticed that the nucleus had fragmented and that there was a secondary nucleus more brilliant than the principal one. This fragment faded rapidly and on March 21st 1916 was seen for the last time. After fragmenting the comet also started to fade until it was last photographed on May 28th, when it was now magnitude 16.
When the orbit was calculated the comet was found to suffer frequent encounters with Jupiter and thus orbital instability. Two very close approaches, one to 0.06AU in 1854 and another to 0.24AU in 1925, combined with other lesser increased the perihelion distance progressively to 1.96AU. A further close encounter with Jupiter on June 27th 2008 (0.158AU) will increase it still further to 2.27AU, making the comet significantly fainter.
With so many perturbations and changes in the orbit the comet was lost after 1916 and its next eight perihelion passages were undetected, thus the comet was considered completely lost. However, the use of computers in orbital calculation allowed the orbit to be reexamined and, finally, on January 25th 1977, Charles Kowal recovered it, close to the expected position, in images with the 1.2-m Schmidt at Mount Palomar. On identification, it was also found on photographic plates taken in November 1976 in Japan and the ex-Soviet Union. The position of the comet corresponded to that of nucleus “b”; despite searches, “a” has not been recovered and is presumed lost.
The current orbit has perihelion at 1.95AU and a period of 6.95 years but, after the 2008 Jupiter encounter, the perihelion distance will increase to 2.27AU and the period to 7.64 years.
The comet was expected to be faint at the 1997 return and to reach only magnitude 17.5. However, in early December, just before the December 12th perihelion passage, the comet started a slow brightening that continued until it reached magnitude 11.5 in March. Although it then started to fade from there it remained about 8 magnitudes brighter than expected.
The most recent perihelion pasaje was on November 30th 2004. The comet was closest to Earth at the start of January 2005 and was thus expected to be brightest at this time, although the 1997 outburst led to some uncertainty in this. The light curve shows a rather flan maximum between mid-November 2004 and late January 2005, with a show fade following from there.
Seichii Yoshida suggests a light curve fit of m1 = 6.5 + 5 log Delta + 30 log r to the upper envelope of the points, although it is fair to say that there is an
enormous dispersion in the data that he presents. This contrasts with the pre-outburst relation in 1997 (based on very few points) of m1 = 8.5 + 5 log
Delta + 30 log r, suggesting that the comet was still about 2 magnitudes brighter in 2004/2005 as a result of the 1997 outburst.
Converted to dust activity in the form of Afrho the light curve shows a strong perihelion asymmetry, although not as marked as the one in 1997.
The peak value of Afrho was reached between T+35 and T+40 days at 40-cm, although Afrho shows little change from T-10 days to T+75 days, before
initiating a rapid decline. Even with the perihelion asymmetry flattening the calculated dependence on heliocentric distance dust production falls as r-14,
very much higher than the normal dependence for Jupiter family comets, showing that this is a very evolved object.