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Last Modification: March 17, 2000
On the 8th of March 1766, the sky having been clear the whole day, I had a mind to make use of this fine weather to look for the satellite of Venus, which for some years has been talked of. I employed, for this purpose, an excellent Gregorian telescope, of 30 inches focus; the great speculum of which, being six inches diameter, magnified objects about 109 times. I could discover nothing with this instrument, the planet appearing only surrounded with small telescopic stars. I likewise made use of a very good achromatic telescope of 5 feet [FL], constructed at Paris, and belonging to the Pr. of S. with which I discovered at about 7 o'clock, and at some distance of Venus, a nebulosity of a small extent, with a luminous center. The time did not permit me that day to assure myself, whether it was a comet or a nebulous star. I was only able, before its setting, to take its position, by comparing it with a star of fourth magnitude, and to defer to the next day the compleating [sic] of the discovery. This very night, after the observation, I looked over my copy of celestial maps of Mr. Flamstead, upon which I have delineated all the nebulous stars, which I have discovered for some years, and found one in that part of the heaven, which I began to see August 25, 1764 [M33]. My description is thus entered in my journal:
"I applied myself to the discovery of nebulous stars, the night between the 25th and 26th of August 1764, and I discovered one near the star Alpha of the great triangle, which I compared with that star, in order to obtain its position. This nebulous star is a whitish spot 15 minutes in diameter; the light nearly uniform, tho' somewhat brighter on the right side; it is seen with difficulty by a common refracting telescope of one foot."Imagining, that what I had then been looking at was this nebulous star, I lost all hopes for the next day. Being, however, impatient to observe the sky, I found in the evening, that this nebulous star had altered its position, being got nearer to the star, with which I had compared it the day before, and which then I found to be the star Eta of the knot of Pisces of the 4th magnitude. I determined the position of the comet with respect to this star, with all the care imaginable, by means of a Newtonian telescope of 4.5 feet in length, furnished with a silken-threaded micrometer. This is the table of my observations:
A Table of the Places of the first Comet of 1766, observed during Part of the Month of March, deduced from the Determination of its Position, with respect to certain Stars.
1766. tr.Tim. Rig.Asc. Dec.Nor. Stars with which the Comet
observ. observ. was compared.
h ' " d ' " d ' "
Mar.8 7 34 22 17 39 46 14 58 11 Com. comp. with Eta Pisc.
9 6 55 4 18 42 46 14 34 40 -----------with the same
7 35 28 18 44 46 14 35 3 -----------with the same
7 47 8 18 45 37 14 31 4 -----------with the same
10 6 49 52 19 45 1 14 10 38 -----------with the same
7 0 23 19 45 31 14 10 37 -----------with the same
7 9 30 19 45 46 14 10 2 -----------with the same
7 40 58 19 47 16 14 9 33 -----------with the same
11 6 58 47 20 44 46 13 46 35 -----------with the same
7 21 37 20 45 31 13 46 10 -----------with the same
7 27 0 20 45 36 13 46 24 Com. with Flam. 31 of Pisc.
7 35 21 20 46 6 13 46 24 -----------with the same
12 6 56 28 21 39 43 13 23 45 -----------with the same
7 5 47 21 40 13 13 23 48 -----------with the same
7 20 38 21 40 43 13 23 52 -----------with the same
7 41 48 21 42 16 13 22 51 -----------with Eta Pisc.
7 51 26 21 44 51 13 23 58 ---------with 101 Pisc.
13 6 49 46 22 31 21 13 1 46 -----------with the same
7 34 17 22 32 1 13 0 19 -----------with Eta Pisc.
7 54 46 22 36 1 13 0 18 -----------with the same
14 6 53 0 23 22 16 12 39 40 ----with Flam. 104 Pics.
7 25 16 23 22 46 12 38 46 -----------with Eta Pisc.
7 47 44 23 25 1 23 38 33 -----------with the same
15 7 6 3 24 5 51 12 18 2 ---with * above 101 Pisc.
7 34 16 24 8 51 12 17 27 -----------with the same
7 58 57 24 9 21 12 17 7 -----------with the same
Table of the Positions of the Star, with which the Comet was compared, reduced to
the time of the Observations.
Rig.Asc. Dec.Nor. d ' " d ' " 19 45 1 14 8 0 Eta of the Knot of Pisc. Comet comp. 8,9,10,11,12,13,&14 20 49 6 13 28 30 101 Pisc. of Flamstead Com. comp. 11, 12, 13, & 15 21 41 24 13 6 30 104 of Pisc. Comet compared the 14.From these observations, Mr. Pingré has computed the Elements of the Orbit of this Comet, as follows.
Place of the ascending node: --- 8s 4d 10' 50"
Inclination of the orbit: -------------- 40d 50' 20"
Place of the perihelium: ----------- 4s 23d 15' 25"
Logarithm of the perihelion dist.: 9.703570
The comet passed its perihelion, the 17th of February, at 8h 50m, mean time at the meridian of Paris.
The motion of the comet retograde.
Remark: [hf] The elements of this comet, dubbed 1766I Messier, are in modern notation:
Ascending node: 100.889 deg, Inclination: 139.154 deg, Length of Perihelion: 246.719 deg, Perihelion Distance: 0.505324 AU, Perihelion passage: 1766 Feb 17.8616 UT
Observations of the second Comet of 1766, discovered at the Marine Observatory at Paris, one month after the former, viz. the 8th of April. By Mr. Messier, &c.
The 8th of April, the sky having cleared up after many days of cloudy weather; on the evening at 8 o'clock, being gone to the Marine Observatory, to observe some transits of stars in the meridian, and looking on the heavens toward the west, I discovered, by my naked eye, near the horizon, and at a little distance from the Pleiades, a comet, which already appeared considerable; the tail was about 4 degrees in length, the light lively, the nucleus very bright and equally luminous with stars of 3rd magnitude. The comet was at a small distance from the brightest star of the constellation musca [now part of Aries], which Flamstead, in the second edition of his catalog, makes of the 3rd magnitude. I several times compared the nucleus of this comet with this star, to deduce its position.
The next day, being the 9th, the sky appearing perfectly serene without a moon, I began to see the comet a few minutes before 8 o'clock. During one hour, it was distinctly seen with the naked eye, the tail was 6 deg or 7 deg in length, the nucleus very bright. I measured its diameter, by comparing it with the thickness of one of the threads of the micrometer of my instrument, and found it about 36" of a degree.
On the 10th, the sky being equally bright, I saw the comet some minutes before 8 o'clock, and between 8 and 9 it was seen with the naked eye, with a longer tail than yesterday, but not so distinct; the nucleus had also lost part of its brightness.
On the 11th, the sky being clear as in the preceding days, the comet could only with difficulty be seen with the naked eye; its appearances were much less distinct than the days before, both on account of the vapors on the horizon where it was, and of the twilight which was considerableand still more so by the light of the moon, which, as well as the two preceding days, was in the part of the heavens, where the comet appeared.
On the 12th, the comet could no longer be seen with the naked eye. Through the telescope it appeared very faint, the tail not exceeding now one degree and a half. It certainly became thus invisible, as well as the nucleus, through the too great power of the twilight.
The 13th, the sky was serene, with some clouds toward the horizon. I looked for the comet, but could not find it, so that the evening of the 12th was the period of its visibility.
1766. tr.Tim. Right Asc Dec.Nor. Stars with which the Comet was
observ. observ. compared.
h ' " d ' " d " '
Apr.8 8 33 54 39 29 56 25 12 16 Com. com. with the star 41 of Aries,
according to Flamstead.
8 57 40 39 25 41 25 11 23 Com. com. with the same
9 6 43 39 24 41 25 10 22 --------- with the same
9 8 7 7 37 59 26 24 26 5 --------- with 33 of Aries
8 7 7 37 59 41 --------- with new Star of 7 mag
8 21 40 37 59 18 24 25 5 --------- with 33 of Aries
8 21 40 37 59 41 --------- with new Star of 7 mag
8 33 4 37 58 41 24 24 20 --------- with 33 of Aries
8 33 4 37 59 41 --------- with new Star of 7 mag
8 44 46 37 58 56 24 25 3 --------- with 33 of Aries
8 44 46 37 58 41 24 24 32 --------- with new Star of 7 mag
10 8 4 15 36 31 15 23 36 46 --------- with Alpha of Aries
8 16 35 36 30 34 23 36 2 --------- with 30 of Aries
8 16 35 36 30 41 23 36 45 --------- with new Star of 7 mag
8 16 35 36 30 56 23 36 49 --------- with the Star of 6 mag
8 36 26 36 29 11 23 36 1 --------- with new Star of 7 mag
8 36 26 36 28 56 23 35 31 --------- with the Star of 6 mag
11 8 6 57 34 57 53 22 33 38 --------- with Alpha of Aries
12 7 39 5 33 29 23 21 39 16 --------- with the same
8 2 11 33 28 46 21 39 1 --------- with the same
Table of the Positions of the Stars, with which the Comet was compared, reduced
to the Time of the Observations.
Right Asc. Dec. Nor. Mag d ' " d ' " 39 3 41 26 17 0 3 41 of Ari accor. to Flam. ded. fr. A. de la Caille's Cat. 38 48 56 24 16 25 6 It is only men. in Flam. Select M. I deter. its Posit. 37 35 11 24 40 51 7 New. I determined its Position 36 46 36 26 2 0 5 33 of Ari accor. to Flam. I determined its Position 35 51 34 23 46 6 7 30 of Ari accor. to Flam. I determined its Position 28 30 38 22 20 55 2 Alpha of Ari deduced from Abbe de la Caille's CatalogFrom my observations, M. Pingré has calculated the elements of this Comet as follows ;
Place of the ascending node: --- 1s 17d 22' 19"
Inclination of the orbit: -------------- 8d 18' 45"
Place of the perihelium: ----------- 6s 26d 5' 13"
Logarithm of the perihelion dist.: 9.804020
It passed the perihelion on April 17, 0h 26' 13" mean time at the meridian of Paris.
The motion of the Comet direct.
Remark: [hf] The elements of this comet, 1766II Helfenzrieder (as this German astronomer had discovered it previously), as derived from Messier's and other observations, are in modern notation:
Ascending node: 178.6515 deg, Inclination: 7.8635 deg, Length of Perihelion: 75.6114 deg, Perihelion Distance: 0.406034 AU, Perihelion passage: 1766 Apr 27.9088 UT
By these elements M. Pingré judged that this Comet might be seen again in the morning, after getting clear of the sun' rays; and the following is an Ephemeris he computed for finding it in the months of May and June.
An Ephemeris of the second Comet of 1766, for the months May and june, at 16h mean time at the meridian of Greenwich.
May Com. Comet's Com. Com. Com. Comet's Comet's
rises Long. Lat.S R.Asc. Dec.S. dist fr dist fr
Earth. Sun
d h h ' d ' d ' d ' d '
1 10 15 52 5 2 3 43 6 3 1 23 0.437 0.709
3 16 15 45 3 0 4 37 4 37 3 3 0.455 0.729
5 16 15 39 1 19 5 26 3 24 4 28 0.473 0.760
7 16 15 32 359 54 6 10 2 23 5 42 0.492 0.773
9 16 15 26 358 41 7 28 1 32 6 48 0.510 0.797
11 16 15 20 357 39 7 28 0 50 7 46 0.528 0.821
13 16 15 14 356 47 8 1 0 16 8 38 0.546 0.847
15 16 15 8 356 3 8 32 359 47 9 24 0.564 0.874
17 16 15 2 355 24 9 1 359 23 10 6 0.581 0.901
19 16 14 55 354 49 9 28 359 3 10 45 0.597 0.929
21 16 14 49 354 18 9 54 358 45 11 29 0.613 0.957
23 16 14 42 353 49 10 18 358 29 11 53 0.628 0.986
25 16 14 35 353 22 10 40 358 13 12 25 0.642 1.016
27 16 14 29 352 56 11 2 357 58 12 56 0.656 1.046
29 16 14 22 352 31 11 23 357 44 13 26 0.669 1.076
31 16 14 15 352 7 11 42 357 30 13 56 0.682 1.105
June 5 356 48 15 3
10 355 58 16 13
15 354 57 17 24
20 353 41 18 37
25 352 10 19 53
30 350 22 21 10
In the months May and June, I sought for the comet in the morning, when the sky was
serene, in the places indicated in this ephemeris, without being able to discover
it: the twilight, which was considerable at the time of the comet's rising, might
hinder my seeing it, and I have not yet learned that it was seen any were else.
Mr. Pingré's remarks on the two comets of this year.
The elements of the first comet I give as absolutely certain, those of the second I cannot be so sure of. The interval was only four days between the first and the last observation. The two last days, and especially the last, the twilight and the moon light must have produced some uncertainty in the observation.
The ephemeris is founded upon the certainty of the elements. Supposing that there was no more than three or four minutes error in the last two observations, this would not much alter the theory from what I have given; but an alternation in the elements would produce two or three degrees difference in the place of the perihelion, which might be sufficient to render the reapparation of the comet uncertain in these high latitudes.
Some German observations sent to Mr. Messier, made in the beginning of April, induce me to conclude, that the place of the perihelion ought really to be placed a little more eastward; but these observations were sent in so confused a manner, that it seems impossible to obtain at least light from them. Perhaps we may hereafter receive from some southern parts, observations sufficient to make out the true orbit of this comet.
Last Modification: March 17, 2000