H. Flaugergues (Viviers, France) discovered this comet in the evening sky on March 25, 1811, in the now defunct constellation Argo Navis. The orbit indicates the comet was discovered when situated 2.72 AU from the sun or at the distance of the asteroid belt. The comet was then low in the south and was moving northward and brightening. An observation by Flaugergues the next night confirmed the cometary nature and his estimated apparent position indicated the comet was in Puppis. Flaugergues further observed the comet on the evenings of March 28 to 31, as well as on April 1.
Observations temporarily ceased after April 1, as the moon began interfering on its way to its full phase on April 8, but resumed on April 11, when J. L. Pons (Marseille, France), not having received word of the discovery, accidentally found the comet on April 11.82 and determined a position on April 11.87. Meanwhile, F. X. von Zach (St. Peyre, near Marseille, France) was able to confirm Flaugergues' discovery on April 11.83.
Johann Karl Burckhardt computed the first orbit for this comet. Using three positions obtained between March 26 and April 19, he determined a rather uncertain orbit which indicated the comet would pass closest to the sun on 1811 September 22 at a distance of 1.77 AU. Burckhardt computed a new orbit during June. Although still parabolic, it indicated the comet would pass perihelion on September 15 at a distance of 1.13 AU. From this orbit, H. W. M. Olbers (Bremen, Germany) noted the comet would become a very bright object during October 1811.
By the end of May, observers were already finding this naked-eye object difficult to see because of its low altitude and entrance into twilight. Flaugergues last detected the comet on May 29, when it was 54 degrees from the sun. Zach last detected it on June 2, at an elongation of 52 degrees. Don Jose Joaquin de Ferrer (Havana, Cuba) last saw the comet on June 15, by which time the elongation had decreased to 41 degrees. The comet's final observer before conjunction with the sun was Alexander von Humboldt (Paris, France). He last caught a glimpse of the comet in strong twilight on June 16.9, at which time the elongation was 40 degrees.
The Earth's steady motion away from the comet culminated on June 25 when their distances had increased to a maximum of 2.4 AU. Thereafter, the distance between our planet and the comet decreased. Meanwhile, the comet's angular distance from the sun continued to decrease and reached a minimum of just under 10° during the last days of July and first days of August.
The comet entered Leo on August 2, and by mid-month was situated almost due north of the sun. The comet was a little less than 19 degrees from the sun on the evening of August 18, and Flaugergues and Olbers were independently searching for the comet shortly after sunset. Olbers was unsuccessful, but Flaugergues was able to spot it very close to the horizon. The comet was then 2.0 AU from Earth and 1.1 AU from the sun. The comet entered the constellation Leo Minor on August 21 and was still almost due north of the sun. Olbers made another attempt to see it on that evening, but was again unsuccessful. adding that his "horizon was not widely free enough"; however, just a few hours later, on the morning of the 22nd, the comet was found very near the horizon, situated 21 degrees from the sun. Olbers added that the nebulosity "brightened toward the middle, but haze and twilight prevented me from distinguishing if it exhibited a nucleus and also something of a tail." Johann Elert Bode (Berlin, Germany) independently recovered the comet with a telescope on the evening of August 22. It was then in the north-northwest and was bright enough to be seen for a short time before it set below the horizon. A few hours later, on the morning of the 23rd, he saw the comet after it had risen above the horizon. It then appeared brighter to the naked eye. Bode also became the first person to detect the comet's tail on this morning and he simply described it as short.
Olbers obtained a good look at the tail during the last days of August using a cometseeker. On the evening of the 28th he saw two rays which he said "formed a parabola, or even a hyperbola." They were separated by an angle of 80 to 85 degrees and each extended 30 to 40 arc minutes. On the 29th he saw a more distinct tail that was broad and 3 degrees long. He added that he could still not distinguish a nucleus.
As the comet began clearing evening twilight, its full splendor was seen by many for the first time. Alexander Ross (a member of the John Jacob Astor expedition traveling down the Columbia River in Oregon) saw the comet on September 1. He "observed, for the first time, about 20 degrees above the horizon, and almost due west, a very brilliant comet, with a tail about 10 degrees long. The Indians at once said it was placed there by the Good Spirit (which they called Skom-malt-squisses) to announce to them the glad tidings of our arrival; and the omen impressed them with a reverential awe for us, implying that we had been sent to them by the Good Spirit, or Great Mother of Life."
On September 8, Simeon Perkins (Liverpool, Nova Scotia) wrote, "at Evening I observe a Comet or Some New appearance of a Star that has an appearance of a Light tail or Blaze it was Nearly in the N.N.W. about one Hour high at 8 o'clock and Set further Northward about [text missing] there was a thin Cloud or haize about it So that I could Not discern the Body of the Star by the Naked Eye but I looked with a Glass and Saw it and an appearance of Light but could not discern any tail or Blaze. It has been observed by Several people for two or three Evenings past."
On September 9, William Herschel (Alnwick, England) saw the comet with a refractor and noted, "the planetary disk-like appearance seen with the naked eye, was transformed into a bright cometic nebula, in which no nucleus could be perceived." He estimated the conspicuous tail as 9° or 10° long and noted a "very considerable" curvature. On September 18, Herschel (Glasgow) observed with a reflector and noted that the star-like head took on the appearance of a globular nebula. He estimated that its diameter was about 5 or 6 arc minutes, "of which one or two minutes about the centre were nearly of equal brightness." He added that the tail was 11° or 12° long and remarked "that towards the end of the tail its curvature had the appearance as if, with respect to the motion of the comet, that part of the tail were left a little behind the head." In addition, "The appearance of the nebulosity...perfectly resembled the milky nebulosity of the nebula in the constellation of Orion, in places where the brightness of the one was equal to that of the other." With a night glass with a field of view of 4° 41', Herschel noted the tail was accompanied by a stream on each side. He noted "that the two streams or branches arising from the sides of the head scattered a considerable portion of their light as they proceeded towards the end of the tail, and were at last so much diluted that the while of the farthest part of the tail, contained only scattered light."
Herschel reported the tail was 25° long on October 6, while the faint outer coma was 15' across. On October 11, Olbers said the tail was 13° long. Herschel noted the tail was 17° long on October 12. He observed with his night glass and remarked "that the two streams remained sufficiently condensed in their diverging course to be distinguished for a length of about six degrees, after which their scattered light began to be pretty equally spread over the tail." On October 14, Herschel estimated the tail length as 17.5°. On October 15, Herschel commented, "in a very clear atmosphere, I found the tail to cover a space of 23 1/2 degrees in length." He added that his night glass showed the preceding branch of the tail was 7° 01' long, while the following was only 4° 41' long. The comet was nearest Earth (1.22 AU) on October 16. Herschel then noted a well-defined luminous point in the center of the coma and measured its diameter as 0.79". He added, "that part of the head which was towards the sun was a little brighter and broader than that towards the tail, so that the planetary disk or point was a little eccentric."
After reaching a maximum elongation of 67° on October 31, the comet began moving back towards twilight. On November 3, Herschel observed with his night glass and noted, "The two branches were nearly of an equal length." On November 5, Herschel estimated the tail was not longer than 12.5°. On November 9, Herschel noted, "The two branches might still be seen to extend full 4 degrees, but their light was much scattered." He added, "The tail of the comet being very near the milky-way, the appearance of the one compared to that of the other, in places where no stars can be seen in the milky-way, was perfectly alike." He estimated the tail's length as 10°. In the reflector, Herschel saw the nucleus "imperfectly" with a magnification of 169x, but "it was more visible" with a magnification of 240x; however, "the nebulosity of the envelope overpowered its light already so much that no good observations could be made of it." On November 10, Herschel obtained only a glimpse of the nucleus in a 10-foot focal length reflector and noted it was as eccentrically placed as on the 4th. He added that the preceding branch was 5° 16' long, while the following one was 3° 31' long. On November 13, Herschel could no longer see the nucleus. He did not that the following stream was now longer and 4° 06' long, while the preceding stream was 3° 31' long. On November 14, Herschel found both streams equal in length and 3° 31' long. On November 15, Herschel noted the following stream was 4° 06' long, while the preceding was 3° 31' long. On November 16, Herschel noted the tail was about 7.5° long to the naked eye and found the following stream 3° 48' long, while the preceding was 3° 13' long. On November 19, Herschel found the two streams to be of equal length and 4° 23' long. The tail was estimated as 6° 10' long.
On December 2, Herschel noted the tail was "hardly 5 degrees long and of a very feeble light." He said the streams were both 3° 12' long. He added, "they joined more to the sides than the vertex, and had lost their former vivid appearance; their colour being changed into that of scattered light." On December 9, Herschel wrote that the tail length had changed little since the 2nd. He noted, "The branches were already so much scattered taht observations of them could no longer be made with any accuracy." On December 14, Herschel wrote that the tail "still remained as before, but the end of it was much fainter."
As 1812 began the comet was moving slowly southeastward through Aquarius some 37 degrees from the sun. On January 2, Herschel commented that the comet "could only be distinguished from a bright globular nebula by the scattered light of its tail, which was still 2 degrees 20 minutes long." Ferrer determined positions of the comet on six evenings during the period of January 5 to 10, and noted, "the sky was very clear, but the light of the comet was so weak that it could scarcely be distinguished with the naked eye." He also pointed out that on January 8, the comet was first seen when its altitude was 16 degrees or 17 degrees, and was last seen when its altitude was only 5 degrees. Barnabe Oriani (Milan, Italy) determined positions on January 7 and 10. Zach's last sighting came on January 11.76, when he was able to make only a semi-precise determination of the comet's position. The comet was then 29° from the sun.
The comet's solar elongation decreased as January continued, dropping to 30 degrees by the 10th, 25 degrees by the 17th, and 20 degrees by the 24th. The elongation had decreased to 15 degrees as February began and had dropped to 10 degrees by the 12th. On February 17 the comet passed only 9.5 degrees from the sun, and then its solar elongation began to increase.
During March 1812, Ferrer took positions he had determined during the period of May 21 to January 8, and computed an elliptical orbit with an orbital period of 3,757 years. He wrote that the comet would arrive at opposition at the beginning of August when the distance from Earth would decrease to 3.14 AU. Ferrer pointed out that on January 8 the comet had been situated 2.86 AU from Earth, so that "it can be scarcely doubted therefore, that it will be visible in its opposition, and in the meridian." He computed an ephemeris for the period of June 1 to August 25.
Ferrer began looking for the comet in early July. He used the refractor of focal length 4.5 feet, "but I could not discover it on account of the little light it had at that time." However, while using a 4-inch refractor on July 11.31, Ferrer spotted the comet with a magnification of only 5x. The subsequent field of view was given as 5 degrees. Ferrer wrote "some stars of the 10th and 12th magnitude surrounded" the comet. He added, "the extremity of its nucleus was in contact with one of these stars, and its centre 2 minutes towards the south, and in the same right ascension." He continued, "The comet appeared as a very slight vapour, its tail opposed to the sun scarcely looked 10 minutes in length" The comet was again observed by Ferrer on July 13 and July 14, but he was not able to determine an accurate position. He even tried using a 12-inch "repeating-circle," but whenever the threads were illuminated, the comet would disappear. Ferrer last saw the comet on July 15.31, and noted it was "in contact with a star of 10th magnitude." The comet entered Capricornus on July 30.
Vincent Wisniewski (Novocherkassk, Russia) found the comet with his Dollond telescope of focal length 3.5 feet on July 31. He described it as faint and blurred, with a coma scarcely 1.5 minutes across, but no tail was seen. He added that it appeared yellowish.
On August 11, Wisniewski observed under not so clear skies with his Dolland telescope of focal length 3.5 feet and described the comet as extremely faint. On August 12, Wisniewski said the sky was clearer than on the previous night and noted the comet was subsequently more distinctly seen. It was about one minute across. He added, "The comet had scarcely the brightness of an 11th-magnitude star." On August 15, Wisniewski said the sky was not very clear and the comet was subsequently extremely faint.
The comet was last detected on August 17.97, 1812, by Wisniewski. He said a strong wind was shaking the telescope and the comet could hardly be seen. The comet was then at an elongation of 167 degrees. It was also situated 3.55 AU from Earth and 4.54 AU from the sun.