NGC/IC Project Restoration Effort

===== NGC 4579 = M 58. This may also be M 91 according to Owen Gingerich in the introduction to "The Messier Album" by Mallas and Kreimer (Sky Publishing, 1978, taken nearly word for word from his Sky and Telescope article in the October 1960 issue, page 196). His reasoning goes like this: Messier picked up all the really bright galaxies in the Virgo Cluster -- there are, according to Gingerich, 13 that Messier saw (not including M 91). He goes on to say, "Inspection of the Palomar Sky Survey photographs shows that Messier was astonishingly successful in locating all the bright galaxies in this area, while he invariably missed the fainter ones. There is simply no bright nebula omitted by Messier that could conceivably be identified with M 91." Well, not quite. First, I count 17 "bright" galaxies in the Virgo Cluster. Here is a list with total visual magnitudes from RC3: Messier NGC V_T Messier NGC V_T Messier NGC V_T 49 4472 8.4 84 4374 9.1 89 4552 9.8 58 4579 9.7 85 4382 9.1 90 4569 9.5 59 4621 9.6 86 4406 8.9 98 4192 10.1 60 4649 8.8 87 4486 8.6 99 4254 9.9 61 4303 9.7 88 4501 9.6 100 4321 9.4 -- 4526 9.8 91: 4548 10.2 Messier not only found 16 galaxies here, but he actually missed a 17th, NGC 4526 that he could have "easily" picked up just over a degree southeast of M 49. I'm not going to suggest that NGC 4526 is the missing object -- it is too far south to have figured in Messier's sweeping on the night of 18 March 1781. This assumes, of course, that Messier actually did sweep in the same way that the Herschel's did, using his telescope essentially as a transit instrument. Even Gingerich who examined Messier's extant records in Paris is not sure exactly how Messier observed on this night, but also assumes sweeping. Let's also assume, following Gingerich's reasoning, that Messier does indeed sweep along a north-south line, picking up stars and nebulae as they appear to move westward across the sky. If this is the case, then the eight Virgo galaxies found on 18 March (M 84 to M 91), listed in RA order in the Connaissance des temps (reproduced in the Messier Album) were measured in that order. M 91 is 40 seconds of time east and 34 arcminutes north of M 90 in the list; there is, of course, nothing there. Gingerich suggests that M 58 is the next bright galaxy in RA order in the Virgo Cluster within the zone swept up by Messier that night. It's position differs from M 90's by 53 seconds east and 1 degree 21 arcminutes south. Gingerich noticed that the difference in declination between M 58 and Messier's position is about 2 degrees -- the actual difference is 1 degree 55 arcminutes -- and suggested a simple digit error of +2 degrees in Messier's published declination. We can test this by asking how good are Messier's positions for the other seven galaxies he measured that night. Here is the table, first for the seven galaxies with the mean differences in RA and Dec shown with the standard deviation and the mean error; next, with modern data for M 58 = NGC 4579 and for NGC 4548 to show the differences with Messier's position for M 91: Galaxy Messier's Position Modern Position Me - Mo M NGC RA (B1781.21) Dec RA (B1781.21) Dec DelRA DelDec s ' 84 4374 12 14 01 +14 07.0 12 13 58 +14 06.1 +3 +0.9 85 4382 12 14 21 +19 24.4 12 14 21 +19 24.3 0 +0.1 86 4406 12 15 05 +14 09.9 12 15 06 +14 09.6 -1 +0.3 87 4486 12 19 48 +13 38.0 12 19 45 +13 36.1 +3 +1.9 88 4501 12 21 03 +15 37.9 12 20 56 +15 37.8 +7 +0.1 89 4552 12 24 38 +13 46.8 12 24 37 +13 45.9 +1 +0.9 90 4569 12 25 48 +14 22.8 12 25 47 +14 22.2 +1 +0.6 ----------- Mean Del +2.0 +0.69 Sigma1 +-2.5 +-0.59 SigmaN +-0.9 +-0.22 Galaxy Messier's Position Modern Position Me - Mo Notes M NGC RA (B1781.21) Dec RA (B1781.21) Dec DelRA DelDec s o ' -- 4579 -- -- 12 26 40 +13 01.5 (-12 +1 55.6) Actual pos. 91 (4579) 12 26 28 +14 57.1 (12 26 40 +15 01.5 -12 -4.4) N4579 + 2d (91) 4548 (12 24 24 +15 41.5) 12 24 25 +15 42.3 -1 +0.8 M pos corr. after WCW The mean differences are +2s and +0.7 arcminutes, both significant at the 2-sigma level (compare to SigmaN). [Incidentally, for a single observation on this night, this means that Messier's positions are good to within 0.6 arcminutes in both coordinates, considerably better than either of the Herschels managed, though that comparison is hardly fair. We'll need to find Messier's standard deviation -- equivalent to Sigma1 in the first table above -- using ALL of his positions, not just those from one night in a restricted area of the sky.] This also means that if Gingerich is correct, the offsets for M 91 -- shown in parentheses in the first two lines of the second table above -- are completely at odds with Messier's measurements for the other galaxies. The 2-degree error Gingerich suggests still leaves large negative differences in RA and Dec for M 58, while the mean differences are positive by much smaller amounts. So, I do not think that M 58 is M 91. The hypothesis put forward by William C. Williams that it might be NGC 4548 (which see) strikes me as much more plausible, given that the position for M 91 derived from his idea -- shown in parentheses in the third line of the second table above -- is well within the statistical errors of Messier's positions for the other seven galaxies measured that night. In addition, NGC 4548 is very nearly identical in brightness to M 98, so Messier could have seen it with whatever telescope he was using then. I do agree with Gingerich, however, that Dreyer's ideas that M 91 might be NGC 4571 (which see) or a comet are almost certainly not correct.

===== NGC 4579 17.5" (4/25/87): bright, moderately large, slightly elongated 4:3 WSW-ENE, small very bright core, stellar nucleus. Located 7.6' E of mag 8.3 SAO 100179. 13": bright, increase to a small bright core, slightly elongated E-W, diffuse halo.