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Page last updated Aug 12, 2017

NGC 16 (= PGC 660)
Discovered (Sep 8, 1784) by William Herschel
Also observed (Sep 5, 1828) by John Herschel
Also observed (Aug 22, 1862) by Heinrich d'Arrest
A magnitude 12.0 lenticular galaxy (type E/SAB0?) in Pegasus (RA 00 09 04.3, Dec +27 43 46)
Historical Identification: Per Dreyer, NGC 16 (= GC 8 = GC 12 = JH 4 = JH 5 = WH IV 15, 1860 RA 00 01 52, NPD 63 03.0) is "pretty bright, small, round, brighter middle". The equivalence of GC 8 (= JH 4) and GC 12 (= JH 5) is discussed in a note at the end of the NGC: "(John Herschel's) h5 (= GC 12) was not seen by d'Arrest and Stephan (per a note in his list XIII); it is = h4 (= GC 8) as they were observed in different sweeps." The position precesses to RA 00 09 04.6, Dec +27 43 46, almost dead center on the galaxy listed above, so the identification is certain.
Discovery Notes: When John Herschel published his General Catalog he listed GC 8 as JH 4 and GC 12 as JH 5, and assumed the latter was equal to WH IV 15. However, d'Arrest equated JH 4 with WH IV 15, and stated that the position of JH 5 was certainly erroneous (per a failure to observe it on Sep 30, 1861), though as critiqued by JH, d'Arrest failed to record a position that could justify that claim (not that d'Arrest could have given a position if he couldn't find the object). On Oct 2, 1882, while observing what became NGC 22, Édouard Stephan concluded that GC 12 (= JH 5) was not in the published position, lending credence to d'Arrest's remarks. Sorting things out for the NGC in 1887, Dreyer decided that JH 4 = JH 5 = WH IV 5 as shown above, and in his 1912 analysis of William Herschel's observations Dreyer stated that WH IV 5 was certainly JH4 (= NGC 16), but with a 1 minute 20 seconds of time error in the right ascension, probably due at least in part to a 1 minute of time error in recording the right ascension. Adding further confusion to the century-old discussion, in 2014 Steinicke suggested that JH 5 and WH IV 15 are not observations of NGC 16, but of some faint star or perhaps even NGC 22. However, as discussed in the lengthy analysis below that suggestion is certainly wrong; and in any event the identification of NGC 16 as PGC 660 is unaffected by any discussion of JH 5 and WH IV 5. So if you want, you can skip that discussion by clicking here.
Analysis of John Herschel's GC 8 = JH 4: John Herschel's GC lists GC 8 = JH 4 as "pretty bright, small, round, brighter middle", with a position of (1860) RA 00 01 52.1, NPD 63 03 27.5, which precesses to RA 00 09 04.7, Dec +27 43 18, less than half an arcmin south of the center of PGC 660 and within its southern outline, so the identification of GC 8 (and NGC 16) with that object is certain. And since JH 4 is the earlier of the two observations in question, its date of observation (Sep 5, 1828) is the correct one for John Herschel's first observation of NGC 16, regardless of the status of JH 5.
Analysis of William Herschel's IV 15: Per William Herschel's first catalog of 1000 nebulae and clusters, WH IV 15 was observed on Sep 8, 1784 as "Stellar, or rather like a faint star with a small chevelure and 2 burs. Faint, small," at a position 2m 6s east and 1° 21' south of 21 (α) Andromedae, or Alpheratz. However, Dr. Corwin has provided me with a copy of the last five observations Herschel took on the night in question, from a "fair copy" made by his sister, Caroline Herschel. That shows that he actually recorded offsets of 2m 6s east and 1° 23' south of 21 Andromeda, and adds other items of interest. Specifically, he noted the rising of the nearly last quarter Moon about half an hour before he stopped observing (because even at that phase the Moon's light would make it difficult to see the faintest objects visible under dark-sky conditions, and the last thing he observed was the very faint object listed as WH IV 15). In the interim Herschel observed three stars: a 7th magnitude star, 21 Andromedae and 85 Pegasi. Since the positions of 21 And and 85 Peg are known, they can both be used to calculate the position of WH IV 15, and in the process provide some information about how consistent Herschel's measurements were on the night in question.
Calculations Using 21 Andromedae: For 21 Andromedae the offsets are 2m 6s east and 1° 23' south. The modern position of Alpheratz is RA 00 08 23.3, Dec +29 05 26, with proper motions of +0.13746"/year in right ascension and -0.16344"/year in declination. This means that in 1784 its J2000 position was 2.0s west and 35" north of its present position, or at RA 00 08 21.3, Dec +29 06 01. This precesses to (1784) RA 23 57 15.7, Dec +27 53 51, and applying Herschel's offsets for IV 15, whatever he observed should be located near (1784) RA 23 59 21.7, Dec +26 30 51. This precesses to J2000 RA 00 10 28.6, Dec +27 43 00, in a completely stellar region about 1m 24s east and 0.8 arcmin south of NGC 16, and about 40s east and 7 arcmin south of NGC 22.
Calculations Using 85 Pegasi, and a Comparison of the Results: For 85 Pegasi, the offsets for IV 15 are 8m 18s east and 34' north. The modern position of 85 Pegasi is RA 00 02 10.2, Dec +27 04 56, with proper motions of +0.78022"/year in right ascension and -0.91775"/year in declination, meaning that in 1784 its J2000 position was 11.2s west and 3' 7" north of its present position, or at RA 00 01 59.0, Dec +27 08 03. This precesses to (1784) RA 23 50 57.5, Dec +25 55 54, and applying Herschel's offsets, whatever he observed should be located near (1784) RA 23 59 15.5, Dec +26 29 54. This precesses to J2000 RA 00 10 22.2, Dec +27 42 03, only a few seconds of time and an arcmin away from the position obtained from comparison with 21 Andromedae, and since William Herschel only recorded right ascensions to the nearest tenth of a minute of time and declinations to the nearest arcmin, errors of up to 0.2 minutes of right ascension and 2 arcmin of declination could be recorded even if the observations themselves were absolutely perfect. As an example, consider the 7th-magnitude star recorded by Herschel 1.5 minutes before 85 Pegasi, at an NPD 15' south of that star. That must be the magnitude 6.5 star HD 224758, which had a position in 1784 (using similar methods of calculation and rounding to the same accuracy as Herschel's measurements) 1.5 minutes west and 13' south of 85 Pegasi, within the range of rounding errors stated above, verifying that for all practical purposes the position of WH IV 15 is exactly the same regardless of which comparison star is used.
Analysis of John Herschel's GC 12 = JH 5 (declared = WH IV 15 in the GC): John Herschel's GC lists GC 12 = JH 5 = WH IV 15 as "very faint, very small, stellar" with a position of (1860) RA 00 03 14.6, NPD 63 04 58.5, which precesses to RA 00 10 27.8, Dec +27 41 46, in the same completely stellar region as the elder Herschel's positions, and less than an arcmin from the average position (RA 00 10 25.4, Dec +27 42 31) of the two values for WH IV 15 calculated above, making its position exactly the same to the accuracy of the earlier observations. So there can be no doubt that JH 5 = WH IV 15, as stated in the GC.
So What Is GC 12 = JH 5 = WH IV 15?: NGC 16 and NGC 22 are the only objects reasonably close to the positions obtained above, so one of those galaxies is almost certainly what the Herschels observed. And the answer is almost certainly NGC 16, since its declination is almost exactly the same as that measured by the Herschels, while NGC 22 is over 7 arcmin to the north, which is a far less likely error than a minute or so of right ascension in historical observations, and NGC 16 is far brighter. Although the listed luminosities of NGC 16 and 22 only differ by a factor of four, that includes the faint outer regions only visible in photographs. For visual observers only the bright core is visible, and the large bright core of NGC 16 is many times brighter than the much smaller, fainter core of NGC 22. In fact, there is considerable doubt whether William Herschel could have seen NGC 22 even under the best of conditions, let alone in the growing light accompanying the nearly quarter Moon rising in the eastern sky. So we are left with three options: (1) Assume that GC 12 represents an observation of a nonexistent object, despite the fact that the Herschels' essentially identical positions suggest they must have seen something, (2) assume that GC 12 represents an observation of NGC 22, despite the fact that it was probably just as hard for them to see as a nonexistent object and the large error in declination is hard to accept, or (3) assume as Dreyer did that GC 12 = GC 8 = NGC 16. Given these choices neither Corwin nor I see any reason to abandon Dreyer's suggestion, and feel reasonably comfortable accepting the probable fact that GC 12 is simply one of many examples in which the Herschels misrecorded the right ascension of an object.
Physical Information: Based on a recessional velocity of 3100 km/sec (and H0 = 70 km/sec/Mpc), NGC 16 is about 145 million light years away, in fair agreement with redshift-independent distance estimates of 105 to 120 million light years. Given that and its apparent size of about 2.3 by 1.3 arcmin (from the images below), it is about 95 to 100 thousand light years across. NGC 16 appears to be a completely isolated galaxy, at least 20 million light years from any other galaxy of significant size.
SDSS image of region near lenticular galaxy NGC 16, also showing the double star listed as NGC 18
Above, a 12 arcmin wide SDSS image centered on NGC 16, also showing the double star listed as
NGC 18
Below, a 2.6 arcmin wide SDSS image of the galaxy
SDSS image of lenticular galaxy NGC 16
Below, a 12 arcmin wide SDSS image centered on NGC 16
Also shown are NGC 18, PGC 655 and PGC 1814072 and 1816642
SDSS image of region near lenticular galaxy NGC 16, also showing the double star listed as NGC 18 and several PGC objects

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IC 5350 - 5386 ← NGC Objects: NGC 1 - 49 → NGC 50 - 99