Harold Corwin

NGC 4505 is probably NGC 4496. Originally found by William Herschel on 23 February 1784, there is no trace of this on the sky. Yet John Herschel claims to have observed it, too, and it is listed in Reinmuth's photographic reobservation of the Herschel's nebulae. After that, however, it disappears from the catalogues except to appear in errata lists. RC1, for example, considers it to be identical to NGC 4496.

Sir William has only one observation of it, and that is referred to a different star than his discovery observation of the nearby NGC 4496, of whic h he has 3 observations altogether. His description of NGC 4505 -- "vF, cL, r " is brief and could just be construed as a hurried observation of NGC 4496 . The positions are not that much different, either.

Sir John's single observation places NGC 4505 close to his father's position. His description is even briefer: "eF; the f of 2 in the field." His right ascension is marked "+-", so it is likely that we shall never know exactl y what he saw, but there are several faint stars near his place that he coul d have mistaken for an "eF" nebula.

Reinmuth's extended description, "eeF, eS, R; = neb * or *14; *8 sp 7', *11.8 sp 2'; NGC 4505, *11.8, *8 in line" pinpoints a 14th magnitude star near Si r John's place. This may be the star that Sir John himself saw and mistook fo r a nebula.

We are left, then, with Sir William's lone discovery observation to explain. Arguing against the equality with NGC 4496 are the different positions, and the fact that both nebulae were found the same night. However, since different comparison stars were used, it is indeed possible that the two observations that night refer to the same object -- NGC 4496. Until Sir William's original observing notes can be scrutinized, I'll adopt the identity as a working hypothesis.

Looking into this again after being directed to Lord Rosse's observation of NGC 4496, I checked the sweep and found some very odd things there. This is 13th object in the sweep (not counting a meteor), and is said to be 11' 45" following 16 Virginis and north by 38 arcminutes. Just a minute of time earlier, however, is another nebula at exactly the same distance north of 16 Vir. Reducing these observations gives positions about 30 seconds east and west of NGC 4496 where there is nothing on the sky. Assuming errors of 1 degree in recording the NPD also leads to areas on the sky where there is nothing. Did William Herschel somehow manage to record NGC 4496 twice? The descriptions are suspiciously similar, too. For the western object, he writes, "A faintish pL nebula, it seems to be resolveable [sic]", and for the eastern, "vF of a consid size; it seems to b e resolvable [sic], is more F than the foregoing and rather larger."

Reading through the rest of the sweep also leads to some rather curious circumstances. For instance, about 45 minutes before William Herschel recorded these two nebulae, he wrote, "An accident happened to the pulleys, but being set right immediately, I suppose it has made no change, neither in time nor zero. " Other objects in the sweep referred to 16 Vir are

William Herschel Position        Modern Position         W - M
RA (2000) Dec       RA  (2000)  Dec     DelRA  DelDec
NGC 4409  12 26 25 +02 29.1  12 26 58.5 +02 29 40   -33.5   -34
NGC 4412  12 27 09 +03 57.2  12 26 36.1 +03 57 53    32.9   -41
NGC 4457  12 29 09 +03 34.2  12 28 59.0 +03 34 14    10.0   -02
NGC 4527  12 33 40 +02 37.4  12 34 08.4 +02 39 14   -28.4  -110

This is an early sweep, and William Herschel was recording his objects with a precision of only of 15 seconds. In this set of seven observations -- the star and the six nebulae -- only 16 Vir, NGC 4409, and NGC 4527 were recorded to that accuracy . The other four are given to a full minute of time only. It's no wonder that their RAs are not very good.

In any event, all this convinces me that William Herschel somehow did in fact record NGC 4496 twice in the sweep, once ahead of its true meridian passage, and once following. I also note that his published offset for NGC 4496 comes from another later sweep where the galaxy was referred to 60 Virginis. That observation is considerably more accurate than the ones recorded here, one of which was apparently taken as the first observation of NGC 4496.

So, the conclusion is that NGC 4505 is indeed identical to NGC 4496.

― NGC Notes by Harold Corwin

Harold Corwin

There are three galaxies in the printed edition of RC3 bearing this number. One of these, VCC 1364 at 12 28 56.4 +04 14 54, has nothing to do with the real NGC 4496 at 12 29 06.6 +04 12 54. This is the brighter of a double galaxy, so is usually called NGC 4496A. Delete the NGC number from the listing for PGC 41450 in RC3. Also delete T, L, B(T), and m'(25).

Also see NGC 5765 for a note about the objects noted as double by William Herschel or John Herschel, but given only a single position.

Finally, see NGC 4505 for a genuine NGC mystery related to this galaxy, rather than simple modern bungling.

― NGC Notes by Harold Corwin

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