View Full Version here: : ngc 5824

08-06-2009, 08:52 AM
NGC 5824 is a very distant globular cluster, 105,000 light years away. That is four times the distance to the middle of our galaxy.
John Herschel, James Dunlop and E E Barnard all claim to have found it in 1831, 1826 and 1882 respectively.

Dr Harold Corwin writes: http://www.ngcicproject.org/corwin/DataFiles/Aug_2006/ngcnotes_5.txt
"NGC 5824 = NGC 5834. Here is an interesting case in which Dreyer reveals his bias for his senior colleague from Great Britian, and against a younger one from Tennessee. But the younger persisted, and proved himself correct.

JH's position (from his Slough sweep number 353 on 9 May 1831; curiously, there is no trace of this in his Cape Observations) is out by 2.4 minutes of time, and 3.5 arcmin; the position is not marked uncertain in any way. His description is also unusual in that it says only, "A very strongly suspected nebula; but I cannot be quite sure (from the low situation) it is not a star." He translated this to "eeF(?)" for the GC, and Dreyer went along with that in the NGC, too.

Barnard first observed this object in 1882, and had four micrometric measurements for it by 1886 when he published a note about it in AN 2756 (he has another earlier note in Sidereal Messenger correcting the description, but quoting JH's incorrect position). The resulting position agrees with the modern positions to within a few arcseconds. Barnard also noted the brief incorrect description in the GC, saying that "The nebula is small and very bright with a decided nucleus."

Dreyer rejected Barnard's identification of the object as GC 4036, listing both it and JH's observation, giving both objects NGC numbers. Another oddity is Dreyer's parenthetical inclusion of Marth's brief note that JH's object is "B, stellar" (I've not yet traced Marth's note). Unfortunately, Dreyer has no other note in the NGC about the two entries, so Barnard's object stands there as a "new" one, while JH's continues on with the wrong coordinates.

Barnard was evidently annoyed by this, and published a second note in AN 2995 (1890) with yet more micrometric measurements, this time from Lick Observatory where he had just taken a job as one of the resident astronomers. This second position is accordant with his first to within a few arcsec, but Barnard gives more details here, noting that the object is probably a globular cluster of 10th magnitude about 3/4 to 1 arcmin in diameter. He also notes that the object must have been quite bright if JH was to have swept it up in the southern sky just six degrees above his horizon at Slough.

This time, Dreyer got the point. So, in the IC1 Notes, he asks that NGC 5834 "be struck out" as it is identical to NGC 5824. Since there is nothing at JH's position, and nothing else in the area that he might have seen, the identity is assured.

Finally, Glen Cozens has suggested that the cluster may have been seen by James Dunlop, too. If Dunlop's RA for his number 611 is corrected by 1.8 minutes of time (21 arcmin) it would match that for the cluster."

Dunlop's 1826 description of NGC5824 = D611 is attached and also given below. He used a 9" aperture speculum mirror reflector to view it 4 times.
Dunlop's description is accurate. John Herschel did not see it from the Cape. Did he see it from Slough?
An image from wikisky.org is also attached. The bright star 28' above N5824 is magnitude 5.4 and the GC is magnitude 9.1.

D611 "A very singular body resembling a star with a burr. The light is equal to that of a star of the 7th and 8th magnitude, and the diameter is not sensibly larger, with various magnifying powers. This has the appearance of a bright nucleus, surrounded by a strong brush of light; and the nebulosity surrounding the bright point has not that softness which nebulae in general possess. I consider this different from nebulae in general."

08-06-2009, 09:55 AM
Interesting Glen.. so did your research show up many errors through the various catalouges ?

Did you get your PHD finished ?

08-06-2009, 10:00 AM
Dunlop's positions are out by about 10 arc-mins on average.
I am still waiting for the markers to look at my PhD. It is about the first three southern DSO catalogues - Lacaille, Dunlop and John Herschel.