IC 847

History and Accurate Positions for the NGC/IC Objects (Corwin 2004)

IC 847 = NGC 4973. Swift's original position -- though not the IC position -- lands within an arcminute of NGC 4973, and his description ("vF, S, R, between 2 stars") fits, too. Interestingly, Howe (in MN 61, 29, 1900) states, "The description `between 2 stars' given in the Index Catalogue, I cannot verify from my sketch of the field of view." One possibility is that Howe's field was much smaller than Swift's unusually large one of 32 arcmin. The two stars are 9 arcmin apart, perhaps separated enough that Howe overlooked one of them.

However, there is another more likely possibility: Howe was examining the wrong galaxy. His position for N4973 is almost identical to Swift's for I847, yet Howe listed it in his third list of "new" nebulae. Why did Howe mistake N4974 for I847? Dreyer made a mistake in precessing Swift's RA of I847 so that the IC RA is 30 seconds too large. This puts I847 so close to N4974 that Dreyer mistakenly equated the two when he got Reumker's correction to the positions of N4973 and N4974 (see NGC 4967 for more discussion of the NGC objects). Howe obviously had not seen Reumker's corrections, though, or he would have realized that his "new" nebula was identical to N4973. This suggests that he thought that the nebula (which we now know as N4974) was I847. This would easily explain why he did not see Swift's stars: N4974 is not between two stars.

Whatever the source of Howe's confusion, it's clear that Swift saw one of the galaxies that William Herschel had discovered a century earlier. Again, assuming Swift's position to be good in this case, that galaxy was probably N4973.