Newton's comet 1680-1681

The comet that was observed by skilled observers, astronomers for first time in history. Newton's cometary theory is based on it. Also it was the first that was discovered telescopically by Gottfried Kirch.

As in the case of previous comets and medals the historical background of this bright comet was described in the Americal Journal of Numismatics Volume XXV. No. 2 in October, 1890 by David L. Walter. Also he gave the detailed description of this token as well as twelve other versions of comet 1680 obverseit. I strongly suggest the enquirer reader to study the original document. Here I cite some of Mr. Walter's original text only with slight modifications (in Italics):

None of the more ancient Comets of which we have any record was so closely observed as this, and of none are there so many medals. It was observed by a large number of scientific people, and it was mainly from observations of this Comet, that Sir Isaac Newton, as set forth in great length in his "Principia" evolved his cometary theory. In Proposition XLI, Problem 21, "from three observations given to determine the orbit of a Comet moving in a parabola'' after giving his calculations and drawings, Newton says, "Let the Comet of the year 1680 be proposed." He then gives a table showing the motion thereof as observed by Flamstead, Dec., 1680, January and February, 1681, and corrected by Halley ; to which he adds some observations of his own made Feb. 25 and 27, March 1, 2, 5, 7, 9, made, as he says, "by a telescope of seven feet, with a micrometer and threads placed on the focus of the telescope, by which instrument we determined the position both of the fixed stars among themselves and of the Comet in respect to the fixed stars." Then follows a vast amount of data, calculations and observations made by divers persons.

Identifying the stars on the medal

According to Halley's stated positions of the comet of 1680 (synopsis, ubi supra), it appears that on the 16th December, the date on the medal, the comet's place was longitude 291.5°, and latitude 18° N. Now in this point of the heavens are the constellations Aquila, Sagitta, Delphinus, &c. Hence the three stars in line, as represented on this medal, are those of Aquila, commonly called the Tailor's Yard.

Proceedings of the Numismatic Society 1838-39. The President's Address, Delivered on the 18th July, 1839. p. 408.

Newton's theories evolved from the observations of this Comet, made by Flamstead, Halley and others, lie at the foundation of all modern learning on the subject of Cometary orbits. He concluded that the bodies of Comets are solid, compact, fixed and durable, like the bodies of the planets, and not as was believed simply exhalations of the earth, sun, or planets. In support of this he says that on December 8 (perihelion), the distance of the Comet from the centre of the sun was to the distance of the earth from the same, as about 6 to 1,000, and the sun's heat on the Comet was to the heat of the summer sun on our own planet as 28,000 to i, and the heat received by dry earth on the Comet about 2,000 times greater than that of red-hot iron with us. By so fierce a heat vapors and exhalations and every volatile matter must have been immediately consumed and dissipated. He further remarks, that after the Comet had been heated by the sun in December, it had a much longer and more splendid tail than in November, when it had not yet arrived at its perihelion, and says that universally the greatest and most fulgent tails arise from Comets, immediately after their passing the neighborhood of the sun. He then combats the theory that the tail of the Comet is simply the beam of the sun's light seen through the head of the Comet, which the advocates of this theory supposed to be transparent ; and also the idea that the tail proceeds from the refraction which light suffers in passing from the Comet's head to the earth ; and concludes that the tails of Comets do not proceed from the refraction of the heavens, but from the Comets' heads, which furnish the matter which forms the tails.

comet 1680He also remarks, that while the atmosphere of the earth illuminated by the sun's light, although but of a few miles in thickness, quite obscures and extinguishes the light not only of the stars, but even of the moon itself, the smallest stars are seen to shine through the immense thickness of the tails of Comets, likewise illuminated by the sun, without the least diminution of their splendor. Newton concludes that the Comets revolve around the sun in conic sections, and are retained in their places by the same force as that which regulates the motion of planets.

Such are a few of the results of his observation of this Comet, and a few of later date, He appears to have given countenance to the calculations of Dr. Halley, by which the orbit of the Comet was calculated at 575 years. Halley observing that a remarkable Comet had appeared four times, at intervals of 575 years, viz: 1. The Comet of September after Julius Caesar was killed, B. C. 44 (the Julium Sidus) ; 2. A. D. 531 ; 3. A. D. 1106, and 4. in 1680-1681, and always with a long tail, calculated the orbit of the latter Comet, and concluded it would return in 575 years, and was identical with those above named. Encke, however, has calculated its orbit at 8815 years instead of 575, and his calculations appear to be considered as correct by modern astronomers.comet 1680 reverse

Obverse. Comet in a starry heaven travelling southwest (on the coin) ; there are twenty stars (exclusive of the Comet) including one very small one between the second and third of the three diagonally sloping large ones. Exergue, A°168o. 16 DEC | 1681. IAN. The edge (of the face of the coin) serrated.

Here I must pause the citation of Mr. Walter. As it visible on the specimen pictured here, there are only 19 stars, and only a dot can be found in the centre of the coin. Maybe it was not clearly visible on Mr. Walter's piece, but it is a similar central dot as on tokens of comet of 1578. It is also interesting that the obverse image fully supports Newton's observation how the stars are clearly shining through the coma, because the engraver placed two of the stars on the picture that should be behind the coma. Whether it is just a coincidence, or the artist also observed the phenomenon we do not know.

Reverse. Inscription : DER | STERN DROHT | BOESE SACHEN : | TRAV. NVR! | GOTT | VVlRDs | VVoL | MACHEN (date in chronogram, i. e. if one sums the bigger capitals as roman numbers gets 1681.) (The star portends evil things ; have faith, God will do well.) [or, make it end well.] Silver.