Herschel I.7

This "object" was observed by William Herschel on January 23, 1784, and described as "vB. L. R." (very bright, large, round) and "A beautiful nebula, not cometic," with the remark "place inac[urate]." When returning to this object, Herschel couldn't find it any more, and first supposed it might have been a reobservation of M61:
I.7. Sweep 105, Jan. 23, 1784: "A beautiful nebula, not cometic. On comparing its place with Messier's Nebulae I find it to be his 61st. It is visible in the finder and vB in the telescope. It precedes 31 Bootis 2h 0.75 m or follows 49 Leonis 2h 6m 45s. These two agree to 12s, therefore a mean correction of both gives +51s, and in present time the R.A. comes out to be 12h 30m 21s." [In pencil, it is added "P.D. 81deg +/-"]
The position given here, RA=12:30:21, Dec=+9deg (1784), precessed to epoch 2000.0, is RA=12:41:18, Dec=+7:49: (2000.0)

Later, he concluded that this early identification was probably erroneous, and that it was presumably a telescopic comet:

Feb. 23, 1784: "The beautiful nebula of the 105 Sweep is not Messier's 61st, as was hastily surmised."

William Herschel's note to this object in his catalog of 1786:

I.7. This remarkable appearance being no longer in the place it has been observed, we must look upon it as a very considerable telescopic comet. It was visible in the finder and resembled one of the bright nebulae of the Connoissance des Temps [Messier's Catalog] so much that I took it for one of them till I came to settle its place; but this not being done till a month or two after the observation, the opportunity of pursuing and investigating its track was lost.

On October 27, 1801, Herschel wrote to Bode [quoted here from J.L.E. Dreyer's Notes to Sir William Herschel's First Catalogue..]:

"After my return from North Wales where I have spent some time I received the favour of your last letter, by Mr. Thoelden. On looking over the sweep in which the nebula I.7 was seen, I find that there is a considerable uncertainty in the polar distance of five successive sweeps, owing to a change in altitude of the telescope and want of well ascertained stars. There was no mistake in writing south for north, but the identity of 49 Leonis is doubtful. My apparatus in 1784 was not so complete as it is now, and to solve the doubt about the place it will be necessary to sweep the zone in which the nebula or rather comet was taken over again. There are objects enough in the sweep to ascertain its place with considerable accuracy, and I will repeat it as soon as the constellation comes to the meridian. Meanwhile I send you two drawings, one representing the appearance of the comet in the finder, the other as it was seen in the field of view of the telescope. From this you see that its situation was within half a degree north following two small stars and about one degree south following a considerably pretty one. The field of view of the finder is three degrees. The comet, by the field of the telescope which is 15 minutes, must have been 4 or 5 minutes in diameter. It had no nucleus, and there was a small star which could not be seen in the finder very near and a little north preceding it."

[H I.7 drawing]

J.L.E. Dreyer, the author of the NGC, comments on this drawing:

The letters P, F, S, N in above sketches are not in the original sketches in Herschel's journal, and everything indicates that he, in January 1784, only used the Newtonian construction. In the sweep (105) this nebula is exactly 2m preceding [west of] a nebula which is undoubtedly II.20=II.148. The R.A. must therefore have been 12h 32.5m (for 1860). The fine nebula M49 is exactly 10m p[receding, westward]., and this nebula has a * 12 mag. [star of 12th magnitude] 4s f[ollowing, to the east]. on the parallel, so that it seems fairly certain that I.7 = M49. In the journal H. wrote next the two sketches, "Messier's 61, I believe," but "61" is strucked out and "49" substituted.

Hartmut Frommert
Christine Kronberg

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