Comets - 73P/Schwassmann-Wachmann - 0073P
Type Periodic Perihelion Date 16 March 2017 Perihelion Distance (q) 1.0 Aphelion Distance (Q) 5.2 Period (Years)   5.4 Eccentricity (e)   0.69 Inclination (i)   11.2 Click for NASA orbit diagram
Hills Observatory: 1 January 2013 to 6 May 2018
Friedrich Carl Arnold Schwassmann and Arno Arthur Wachmann (Hamburg Observatory, Bergedorf, Germany) discovered this comet on photographs exposed for a minor planet survey on 2 May 1930.  The comet was then described as diffuse and magnitude 9.5. A few days later, H. Schneller (Berlin-Babelsberg Observatory, Germany) found prediscovery images on photographic plates exposed on 27 and 29 April. The comet is intrinsically faint and, when combined with the slight variation in the computed orbital period and a very unfavorable apparition at its first predicted return in 1935-1936, it became lost after the 1930 appearance. Searches during the next several apparitions failed to locate the comet. Further complicating things was an approach to within 0.9 AU of Jupiter during October 1953 and 0.25 AU in November 1965. Revised orbital computations by Belyaev and Shaporev in 1973 led to the recognition that although the apparition of 1974 would be very unfavorable, the comet's return in 1979 would be the most favorable since 1930. J. Johnston and M. Buhagiar (Perth Observatory, Australia) reported the discovery of a comet on plates exposed during a minor planet survey on 13 August 1979. Confirmation was made on 15 August and M. P. Candy (Perth Observatory) noted the comet's direction and rate of motion resembled what was expected for the lost comet Schwassmann-Wachmann 3. This was confirmed and the comet's perihelion date was found to be 34 days later than predicted. The comet attained a maximum magnitude of 12.5 as it passed closest to Earth (1.4359 AU) on 19 March. The comet was missed during the 1985-86 apparition, but was observed in 1990. This was the best appearance since 1930. On April 17, the comet passed 0.3661 AU from Earth and reached a maximum magnitude of 9. The 1995 appearance was not supposed to be a very good one with the comet's closest approach to Earth on 1995 October 17 (1.3114 AU) being nearly 1 AU further than the exceptional 1990 apparition. The comet was meeting the expectations of astronomers when it was seen by K. Kinoshita (Japan) on August 19 at magnitude 12.9, but then something happened. Astronomers using the Nancay Radio Telescope were monitoring the comet's emissions during early September, just after the comet's minimum elongation from the sun on 31 August (40 degrees), when they detected an increase in OH on 8 September. The emissions continued to increase through the 13th. By the 17th, the comet had moved far enough out of the sun's glare to enable visual observations and the brightness was found to be magnitude 8.3. That brightness more or less held until the beginning of October, when several observers reported it had increased to magnitude 6. Although the comet was still in twilight and at a low altitude, it was then visible in binoculars as a slightly diffuse star. The comet faded slightly thereafter and then underwent a third outburst back to 6.3 on 22 October. The comet faded very slowly after its last outburst. Although it was then moving away from both the sun and Earth, observers continued reporting the total magnitude as 7.5 to 8 through the end of November and 8 to 8.5 through the first two- thirds of December. The comet became more diffuse during the remainder of December and into January and a rapid fading finally set in during the latter month. By February the brightness had dropped back to magnitude 14. Another surprise came in December when observatories began reporting mulitple nuclei within the coma of the comet. Four nuclei were officially designated and were labeled "A", "B", "C", and "D"; however, "D" was not observed elsewhere and may have been a very short-lived condensation. Three additional condensations were reported, but not designated, because they were also not seen elsewhere. Component "A" was discovered on 23 December 1995 and was last detected on 18 February 1996. Component "B" was discovered on 23 December 1995  and was last detected on 14 December 1996. Component "C" turns out to be the main body of the comet and was followed until 14 December 1996.  Z. Sekanina published an article in the International Comet Quarterly (2005) that offers an excellent argument that the observations attributed to component "B" during 1996 may actually belong to two different components. He suggests "B" was seen up to the time the comet became lost in the sun's glare after February, while component "E" was seen from September to December. Since "E" was officially discovered i n 2000, this could be considered prediscovery observations. The comet's next return to perihelion occurred on 27 January 2001. Although it was poorly placed for observation, the comet was again widely observed because it was brighter than expected. In addition, two of the nuclei seen in 1995 were back: Component "C" was recovered 5 January 2000 and was observed until 20 November 2001, while Component "B" was recovered on 19 November 2000 and was observed until 27 July 2001. At the next predicted perihelion date of 7 June 2006 the comet would pass 0.0735 AU from Earth on 13 May, being only slightly farther away than during the original discovery apparition of 1930. C. W. Hergenrother (Lunar and Planetary Laboratory) recovered the brightest component, referred to as "C", while using the 1.2-m reflector at Mount Hopkins on 22 October 2005. He gave the magnitude as 19.3 and said the strongly condensed coma was 6 arcsec across. There was also a fan-shaped tail extending 8 arcsec in PA 300°. Component "B" was found at by J. A. Farrell (Jemez Springs, New Mexico, USA) on 2 January 2006, while using a 41-cm reflector. He gave the magnitude as 18.8-19.0, which was then just over three magnitudes fainter than component "C".  The next component found did not match the prediction for any previously observed component and set the stage for many new discoveries as the comet approached perihelion. This new component was labelled "G". It was independently found by R. A. Tucker (Tucson, Arizona, USA) on February 20 and 22, and E. J. Christensen on Mt. Lemmon Survey images obtained on 24 February. The magnitude was given as 17.2. Numerous other components were found in the weeks that followed. Currently there are 67 components.  The major fragments of this comet are "B", "C", "G", and "R", with "C" being the main comet. Date 10x10 mag Error Kphot mag Coma ' 10-Jan-17 15.60 0.07 14.1 0.5 27-Jan-17 14.93 0.05 13.2 0.4 06-Feb-17 14.68 0.06 12.7 0.4 20-Nov-17 18.22 0.06 16.7 0.2 B-component 03-Jul-17 16.82 0.01 15.1 0.5 21-Jul-17 17.57 0.12 15.7 0.3 31-Jul-17 18.07 0.16 15.9 0.3 04-Aug-17 17.59 0.20 16.4 0.3 24-Aug-17 17.08 0.03 16.3 0.4 28-Aug-17 17.05 0.03 15.7 0.6 16-Sep-17 17.16 0.02 15.9 0.5 27-Sep-17 16.95 0.04 15.8 0.4 18-Oct-17 16.84 0.02 15.4 0.5 25-Oct-17 17.00 0.02 15.0 0.4