NEAT PLANETARIES : 8 NGC 2438 in Puppis
NGC 2438 / H IV 39 / h.463 / h.3093 / Sa2-13 /
VV′ 69 / ARO 46 / PK 231+04.2 / PN G231.8+04.1
(07418-1444) + NGC 2437 / M46 / H IV 39 /
h.464 / C* 0739-147 / OCl 601 (07417-1449) [U274/U275] lies
some 14°E of Sirius and one of the best deep-sky
objects in Puppis.
Cluster M46 is quite obvious in binoculars, however, the
pale blue planetary may only be seen with care in 10.5cm.,
and on the rare occasions, in 7.5cm. Although open star
cluster is fairly run-of the-mill in nature, it is
certainly greatly enhances in the minds of visual observers
by the fact that it also contains the brightish planetary
nebula (PN), NGC 2437. The planetary lies on the north
eastern boundary (nf. north-following) of the open
cluster, roughly about two-thirds the distance from
NGC 2437 central core. It remains a particularly favourite
object in our summer skies from our southern hemisphere, as
it is very conveniently placed near the zenith in the sky
from mid-southern latitudes.
NGC 2437/38 : Open Cluster /
Planetary. Image size:
12½′×12½′
Source: ALADIN previewer (Red: AAO/R/DSS2; Blue: SER/I/
DSS2; Green: average. Red/blue image modified by
Silvering with reduced saturation.
The larger open cluster, NGC 2437, spans about
25″ across, fitting easily in medium powers in
5cm or 7.5cm telescopes. Total magnitude is a bright 6.1v
or 6.33B, making the cluster among the brightest of the
medium clusters. NGC 2437 contains about 150-odd visible
member stars, and looking just to the north-east, within
the cluster’s boundary, is the approximately
1.0″ (60 arcsec) diameter planetary. Deep images show
the nebula is not round as it is by eye, but is slightly
oval whose dimensions are about in about 73×68 arcsec,
being aligned at about 30° from north (position
angle).
NGC 2438’s lovely planetary nebula is 10.8v /
10.1b (11.7B?) / 10.2r magnitude, was VV classification is
4+2
In 20cm. telescopes, using medium to high magnification,
NGC 2437 looks slightly oval or even annular, shining
its obvious nebulous lustre very nicely with its pale and
slightly mottled centre. It responds very well with an
O-III filter, which is a useful device to also eliminate
the many stars of the open cluster and allow the amateur
observer to concentrate their attention just on the surface
texture of the extended planetary disk.
Such cluster-bound planetaries are not totally unique to
open clusters, as another bright example is the Pyxis
PNe/cluster combination, NGC 2818/2818a. (NSP 25.)
Historical Interlude
This planetary nebula was discovered by Sir William
Herschel on 19th March 1786, and catalogued as H IV 39. The
open cluster, without seeing the planetary, was first
spotted by Charles Messier in mid-winter on 19th February
1771, who catalogued it as the first object in the second
part of the Messier Catalogue.
It was later divided in the catalogues as separate objects
by John Herschel as h.463 and h.464; and combined as
h.3093. It now remains as separate objects as, NGC
2437 (Open Cluster) and NGC 2438 (PNe), within
the New General Catalogue (1888).
Charles Messier describes the open cluster as;
Messier Catalogue Extract for
M46 From Third Version from 1781, published
in the Connaissance des Temps, objects 1 to 103.
(1784).
Text version;
“Amas de très-petites
étoiles, entre la tête du grand Chien & les
deux pattes de derrière de la Licorne,
déterminé en comparant cet amas à la
2.e étoile du Navire, 6.e
grandeur, fuivant Flàmftéed; on ne peut voir ces
étoiles qu’avec une bonne lunette; l’amas
contient un peu de nébulofité”
Best translation for this simply reads;
“Cluster of very-small stars,
between the head of the big Dog [Canis Major] and two hind
paws of the Unicorn [Monoceros], determined by comparing
this cluster with the 2[nd] star of the Ship [2 Navis], 6th
magnitude, according to Flamsteed ; they can see these
stars only with good telescopes; the cluster contains a
little nebulosity.”
Other Messier’s Translations of M46
The commonly accepted version by reads;
“A cluster of very small stars,
between the head of the great Dog and the two
hindlegs of the Unicorn, determined by comparing
this cluster with the 2nd star of the Ship [2 Navis], of
6th-magnitude, according to Flamsteed; the stars are not
visible except with a good refractor; the cluster contains
a bit of nebulosity.”
Yet another partially reasonable and well-quoted version
appears in Jones (1975), which says;
“A cluster of very small stars
between the head of Canis Major and the two hind
paws of Monoceros, determined by comparing this
cluster with star 2 Navis, 6th magnitude, following
Flamsteed; the stars cannot be seen except with a good
telescope; the cluster contains a little
nebulosity.”
I continue to be quite appalled with the often gross
deliberate distortions of observational descriptions or
of foreign translations made by mostly lazy amateur (and
sometimes professional) astronomical writers. It seems that
most are far too lax to go and examine the actual original
source material, and find what is truly said. Many just
appear to copy verbatim other works, or worst, just
readjust the copied text to make their own words appear as
something “original”. Such continued reworking
means that the quoted translation ends up totally wrong
— significantly having implications interpreting what
the observer is properly saying. This often perpetuates
into the next author who does the same, again making any
analysis or guidance almost totally worthless (The science
ethic of being honest and truthful goes out the window,
especially when it is not attributed nor referenced from
the source in which it came.;
For example, the writer Tammy Plotner at
Universe
Today, has given the distorted translation that
does not appear anywhere else. It is quite likely rewritten
(but not referenced) from the on-line deep-sky reference
source called SEDs, under object / webpage on M46. She
writes in her
M46 article;
“A cluster of very small stars,
between the head of the Great Dog and the two
hind feet of the Unicorn, [its position] determined
by comparing this cluster with the star 2 Navis, of
6th-magnitude, according to Flamsteed; one cannot
see these stars but with a good refractor; the
cluster contains a bit of nebulosity.”
I have underlined here the distortions to highlight the
possible misinterpretation in what Messier is truly
describing. I spent a few hours investigating what I could
find of Messier’s quotes by others, and found
contradictions everywhere.
Take for example the critical quote by Messier of;
“l’amas contient un peu de
nébulofité”. The words here have been
translated as either; “…contains
a bit of nebulosity”,
“…contains a small
nebulosity”, or “…contains
some nebulosity”
Another common mistranslation is deux pattes de
derrière, which in English means “two hind
paws”, where patties in French is directly
translated as meaning “paws), which is the
proper interpretation of these words. Hence, words like ‘hindlegs’, ‘feet’ or even
‘legs’, or any variation of these, is not
correct.
Also, the best translation from the French is that the
cluster “…contains a little
nebulosity.”, which clearly has a quite different
implication. Either Messier is saying that the open cluster
appear slightly nebulous or is he saying he sees a little
nebula?
Some two years later, William Herschel then
catalogued both cluster and then the nebula as H IV 39. He
first says of the cluster;
“A beautiful, very rich, compressed
cluster of stars of various magnitudes.”
Herschel (1789) then, from an observation made on 19th
March 1785 describes;
“pB. R. r. [Pretty bright, Round,
]” within the 46th of the Connoiff. des Temps
almosft of an equal light throughout 2′ dia. no
connection with the clufter, which is free from
nebulosity.
John Herschel (1847) later describes;
“A very fine PLANETARY NEBULA,
oval, uniform in light, and of a very flat appearance;
rather faint ; diam[eter] in R.A. = 4′.0 ; has a
☆ 15m on it, and one 13m close to its border.
The object is excentrically situated in a superb cluster of
stars 12…16m (46 Messier).”
On another viewing he sees;
“A fine, nearly uniform, slightly
elliptic PLANETARY NEBULA, 40″ dia[meter]. A
☆14 m, is excentrically situated in or in it,
which is doubtlessly only superimposed and belongs to the
cluster Mess 46, in which (somewhat north of the most
compressed part) this object is situated. A very uncommon
and indeed unique combination, if No.3154 be not the case
in point.”
William Parsons, the Third Earl of Rosse, in his
publication; “Objects drawn by Lord Rosse and
Johnstone Stoney” (1850), who made a useful
sketch (No.12.) at Birr Castle in Ireland on 22nd December
1846, using the speculum 1.8-metre (72-inch) telescope
— sometimes named, the Leviathan of
Parsonstown. [Incidentally, this book also shows the
very famous spiral galaxy sketch of M51 / NGC 5194
(13299+4712) in Canes Venetici. I could not find this
specific book or image from it, however, reference to M46
(h.464) appears, including discussions on the appearance,
observational methods and the telescope in the on-line
“Observations on the
Nebulae”, Phil.Trans.Roy.Soc. London,
140, 499 (1850). Here contains the
words;
“The five planetary nebulae we have
ascertained to be annular, are as follows: [h.]464 [M46],
Plate XXXVIII. Fig 12., has two stars within
it;…”
Parson’s series of visual observations appear on
pg.513-4, which are described as follows;
Fig.12, H. 464 —“Annular
nebula at the edge of the cluster M. 46. Sketched
22nd December 1848 annular, two stars in it.”
January 27, 1849.—“A third
star suspected in brightest part.”
January 29, 1849.— “Third
star strongly suspected.”
February 13, 1849.— “Observed
nothing further.”
March 16, 1849.— “Saw but two
stars in it”
Comment 1: This paper additionally
contains several planetary nebulae, including the famous
eerie face of M97 / NGC 3587 / Owl Nebula
(11148+5501). All serious planetary nebulae observers
should acquaint themselves with the text on pages 567/8 of
this paper — if only to understand the evolution of
early PNe observational descriptions.
Comment 2: According to modern
class historical deep-sky book by Webb Society member;
Steinickle, W., p.299 (2010), an an unknown star discovered
by William Parson, that maybe a possible suspect nova, in
which Steinickle states;
“A similar case of a supposed
nebula is the double star 2 Puppis (6 mag), 50′ east
of the planetary nebula NGC 2438 (GC 1565), which belongs
to the open cluster M 46. Lord Rosse noted on 28 January
1849 that it was ‘very strongly nebulous.’ But
wait, there is more: ‘Another B neb star about
10′ nf the D star.̱ This is 4 Puppis (5
mag).
Admiral William H. Symth, in his famous “A
Cycle of Celestial Objects” or just
‘Cycle’ that was originally published in
1840s.
“A very delicate double star in a fine cluster, outlying the Galaxy, over Argo’s poop. A 8½, and B 11, both pale white.
A noble though rather loose assemblage of stars from the 8th to the 13th magnitude, more than filling the field, especially in length, with power 93; the most compressed part trending sf. and np. Among the larger stars on the northern verge is an extremely faint planetary nebula, which is 39 H. IV., and 464 of his son’s Catalogue. This was discovered by Messier in 1769, who considered it as being “rather enveloped in nebulous matter;” this opinion, however, must have arisen from the splendid glow of mass, for judging from his own remark, it is not likely that he perceived the planetary nebula on the north.”
Here Smyth is attributing discovery of the planetary
nebulae to Charles Messier
Did Messier Discover the Planetary Nebula in M46?
Arguments for Messier discovering the nebula in M46 is
of course the quality size of the aperture he was using,
and that it was too small to be able to see the faint disk.
The other is, the interpretation by the Herschel’s
(and other subsequent observers), who claim the apparent
nebulosity he sees is the partially unresolved star cluster
that Messier does not seem to describe.
This point I think remains debatable. Messier’s
failure comes back to his rather inadequate description,
who does not describe where exactly the planetary nebula
lies among the surrounding cluster stars nor the direction.
I have often thought in the back of my mind, the real
suspicion that Messier had doubts on what he was seeing.
This is especially in the light that his deep-sky catalogue
was in the most part hunting for fuzzies that might
be mistaken by others as new undiscovered comets. This is
why the text is written in the third person, so that when
someone read his catalogue, those observers would not fall
into the trap of really seeing a deep-sky object rather
than comets. Messier could not care much for the niceties
of describing the objects in minute detail (unlike the
Herschel’s, for example) but only to avoid these
deep-sky objects as uninteresting or unimportant
“comet traps.” This is likely why the
descriptions are so focussed on nearby stars close to the
catalogued nebulous (or possibly interpreted as a nebulous)
deep-sky object.
Few do seem to seriously take such general ideas into
consideration — as nothing written for more than
century or more after the event is really questions by
today’s visual observers. Our astronomical
experiences are now often too totally unrelated to the
conditions and quality of the older telescopes that people
like Messier were once using. Moreover, they knew
virtually nothing of the reality of the natures of most
deep sky objects, nor of the variety and morphology of
their structures or inherent variations. The last comment
here is also with real rivalry and nationalism between
many observers, who, after decades after their works were
usurped and questioned for their shortcoming within the
crude descriptions or analysis — whose many
vulnerabilities were easy to exploit — especially as
no one could discuss with them as they were no longer
living. This problem here is a European viewpoint of
competition. I.e. Mostly French and England, and in some
instance, the Germans, Spanish or Italians (It still
happens historically and continues even today!)
This I think is a realistic view of some of the primary
issues here in Messier seeing the planetary nebula or
not.
Modern Observation Descriptions
There are so many modern observational descriptions for
this object it is very hard to pick out the better ones!
These ones here below show the evolution and comparison of
observational description, especially in light of the
earlier observers not knowing if these objects were truly
nebulous or unresolved stellar conglomerations. When
Englishman William Higgins use the spectroscopy on these
objects in 1864, PNe became the nebulous objects we are
familiar with today.
a.) Rev. Thomas W. Webb in “Celestial Objects
for Common Telescopes” (COfCT.), Vol.2,
pg.38; Dover Edition (1962); gives he own views on M46 and
the PN. Webb places the object in Argo, and rather
cryptically says in his own unique but difficult
abbreviated style;
“2437 (M 46.) VIIh 38.1 S. 14°
38′. Beautiful circular cloud of small stars
(H[erschel to 10 mg]) about ½° in
diam[eter] : a little p[receding] the group round 4. nearer
to it than [NGC] 2422. 2438 a feeble neb[ula] on its
N[orth] verge is in La[ssall]’s 20-ft. refl[ector]
‘an astonishing and interesting object’ ; he an
E[arl] of Rosse, see it annular ; so Buffham, 9-in[ch]
‘With’”
b.) According to the late 19th early-20th Century
Serbian-Austrian amateur astronomer, Leo Brenner
(1855-1926) [Brenner (1902)], who is better known to me for
his Venus observations (Aguirre (1995)), and also
referenced in Stoyan (2008), suggests this is a;
“Splendid object, even for smaller
telescopes. 30′ diameter, very rich and bright. Stars
of 10m and lower. The cluster contains a planetary or
ring-shaped nebula of 3.75&8242;[?] diameter and of
considerable brightness.”
c.) Heber Curtis (1918a) sees;
“a very large, bright, sparse
cluster about 25′ in diameter, in which is involved
the planetary nebula 2438.”
Curtis (1918b) gives the PN is a Class II — Ring
Form planetary, whose photographic image is described;
Plate XII. Exposure 3h. “The
fainter star at centre is perhaps the central star; magn.
16. The nebula is avery irregular, broad, patchy ring
38″ in diameter; it lies in a cluster (NGC 2437).
The star at SW lies in a gap in the ring, the others seem
to be simply projected on the nebula/ Ring quite faint.
Rel. Exp. 50”
c.) E.J. Hartung in AOST1 says for Object No.274,
in one of the best descriptions in the whole book, That
NGC 2437−8 is;
”A beautiful open cluster with
medium bright stars about 25′ across, rich and
broadly concentrated towards the centre. In the Nf. region
is a pale bluish planetary nebula 50′across which on
closer examination will be seen to be annular with paler
centre and single prism image. Several stars are projected
upon it for the nebula at 1,600 pc. lies far behind the
cluster at 700 pc. Messier discovered the cluster in 1771
but did not see the nebula, which however is plainly
visible with 10.5 cm amongst the stars.”
d.) In Webb Society Book on Planetary Nebulae Vol.2 by
Jones (1979), on pg.64, the visual observations of 2438 are
as follows
(16½)[-inch] “Annular, N.f.
part of ring brightest; ×419 little extended N.p.,
S.f.; star seen.
(12) Slightly irregular greeny-white patch on the NE
edge of open cluster M46.
(8) Fairly large roundish patch with star on E edge; no
trace of structure or PA.
(6) Circular at LP [low power]; at HP [high power] seems
involved in star close S.f. ”
e.) Canberra Astronomical Society member Albert Brakel,
in the Journal Southern Cross, in his series of
articles entitled “Constellation of the Month
— The Ten Best Southern Planetaries (2007),
details this 2438 as;
“This one is included not so much
for its own sake but because of its outstanding setting, in
the northeastern part of the open cluster M46 in Puppis. It
is pale bluish, easy to see, and 60″ in diameter.
Close inspection shows that its outer perimeter is a bit
brighter than the rest. The cluster isn’t too bad
either — rich, about 25′ across, and broadly
concentrated towards the centre.”
f.) Steve Coe, using 13.1-inch f/5.6 describes;
“NGC 2438 Bright, large, elongated
1.2×1 in PA 75, the central star is easy at 100×.
Raising the power to 440× brings out several dimmer
stars involved in the nebula. Also at the higher power the
shape of the planetary is seen to be an incomplete ring,
somewhat like a horseshoe. This bright rim is about
270° around and is dimmest on the north side. I have
always seen this planetary nebula as light green in color.
This is from a great night at Sentinel, 7/10 seeing and
10/10 transparency.”
Then Steve at the Ultimate Star Party, McDonald
Observatory in October 1995, S=7, T=9, using 25-inch
f/5;
“NGC 2438 the planetary in Puppis
25′; 12mm; light green, 3 stars, 2 obvious, one
tougher, annular, central section light grey, two layers of
nebulosity surround the central star.”
Technical Data on NGC 2438
Both the open cluster and PNe were earlier estimated to
be about 1.8kpc. from us, though many sources consider that
the PNe is certainly closer, therefore being superimposed
on top of the more distant cluster. Others like Knarchenko,
et al. (2005), find the cluster distance as 1.3 kpc., so
this is still a real issue of some contention. Adding to
the problem is the measured radial velocity for the
planetary being +75.4 km.s-1, while the cluster
is a more pedestrian +48.09 km.s-1 (Knarchenko,
et al. (2005)) Here one would be expecting that cluster
star velocities that are gravitationally bound membership
would only differ by merely about 5 km.s-1.
A recent distance, according to Stanghellini, Shaw and
Villaver (2008) using 6cm. radio emissions and the observed
expounding boundary of 35.2 arcsec, find distance as 1215
pc., rounded to 1.2 kpc. or 0.6 kpc. further to us. Some
astronomers say the exact opposite, that the planetary is
in the distance. So the jury maybe still out!
Perhaps one of the most definitive paper on the
association of this PN and the open cluster is Kiss et al.
(2008)
Deep images of NGC 2438, I.e.
APOD
Image taken by Daniel López using the Spanish
Observatory telescope (Instituto de Astrofísica de
Canarias or IAC) on the Canary Islands, shows a further
annular circular ring with the radius about 2 arcmin (120
arcsec), with another, even fainter and more extended
bubble or halo, is out to about 4½ to 5 arcmin. The
literature says this extends in true distance to about 1.2
parsecs or 4½ light-years — atypical of most
PNe. All these structures suggest the the nebula ejection
has undergone various traumatic phases as the star evolved
from the swollen red giant to its planetary nebula nucleus.
One can imagine that three or four distinct phases have
occurred within the lat few millennia to the object we now
see today. Yet there are other features here to discern.
For example, on the northern boundary is an unusual kind of
windswept mottling or interaction with interstellar winds
that have disturbed the nebulosity’ symmetry. The
cause of this is now under investigation.
Age of NGC 2438
In Stoyan, R., et al. (2008), they claim the planetary;
“Much younger is the planetary nebula NGC 2438,
only about 45,000 years old,…”
Central PNN of NGC 2438
A faint central PNN star discovered by C.M. Anderson in
1934, who estimated the brightness as 17.5v at 479.3nm..
It has been recently found to be brighter at
17.2±0.02v magnitude (Gathier & Pottasch (1988),
whose estimated temperature is about 75,000K. Zanstra
temperature is a higher value of 131,000K, and lies the
very upper range of the accepted PNNe temperatures. The
flux at 479.3nm. is a very high
1.26±0.11×1013, which normally for
most PNe is in the order of values around 10-16.
This suggest this planetary might be only several thousand
years old. This PNN is also not exactly central to the
symmetry of the nebulosity, being off-centre by about 7
arcsec toward the NNE.
NGC 2438 has been well-studied in the literature for
more than a century, but there are still many secrets to
unlock here.
References for NGC 2438
- Anderson, C.M., “The proper motions of
thirty-three planetary nebulae.”,
Lic.Obs.Bull., 17, 21 (1934)
- Aguirre, E.L., “Forgotten Legacy of Leo
Brenner” section ‘Amateur
Astronomers’, S&T., p.100-102,
August (1995)
- Brenner, L., “Beobachtungs-Objekte für
Amateur Astronomen” Pub. Meier, Leipzig (1902)
[In German]
- Armsdorfer, B., Kimeswenger, S., Rauch, T.,
“Photo-Ionization Modelling of the Multiple Shell
Planetary Nebula NGC 2438”, HvaOB,
26, 49 (2002)
- Curtis, H.D., “Descriptions of 762 Nebulae and
Clusters: Photographed with the Crossley
Reflector.”, Pub. Lick.Obs., 13,
11, Part I (1918a).
- Curtis, H.D., “The Planetary
Nebulae.”, Pub. Lick.Obs., 13, 55,
Part II (1918b).
- Gathier, R., Pottasch, S.R., “Magnitudes of
central stars of planetary nebulae.”,
A&A., 197, 266 (1988)
- Herschel,W.“[XX.] Catalogue of a Second
Thousand of New Nebulae and Clusters of Stars; with a few
Introductory Remarks on the Construction of the
Heavens.”, Phil.Trans.Roy.Soc. London,,
79, p.212 (1789)
- Jones, K.G., Ed., “Webb Society Deep-Sky
Observer’s Handbook : Volume 2, Planetary and Gaseous
Nebulae”, Pub. Lutterworth Press, New Jersey
(1979)
- Jones, K.G., “The Search for the
Nebulae.”, p.67, Pub. Alpha Academic (1975)
- Kiss, L.L., et al., “AAOmega radial velocities
rule out current membership of the planetary nebula NGC
2438 in the open cluster M46”, MNRAS.,
391, 399 (2008)
- Knarchenko, N.V., et al., “Astrophysical
parameters of Galactic open clusters.”
A&A., 438, 1163 (2005)
- Parsons, W., “Observations on the
Nebulae”, Phil.Trans.Roy.Soc. London,
140, 499 (1850)
- Pauls, R., Kohoutek, L., “Study of the
planetary nebula NGC 2438. I. Spectroscopy of the nebula
and of some cluster stars”, AN.,
317, 413 (1996)
- Stanghellini, L., Shaw, R.A., Villaver, E.,
“The Magellanic Cloud Calibration of the Galactic
Planetary Nebula Distance Scale.”, AJ.,
689, 194 (2008)
- Steinickle, W., “Observing and Cataloguing
Nebulae and Star Clusters : From Herschel to Dreyer’s
New General Catalogue. p.299 (2010)
- Stoyan, R., et al., “Atlas of the Messier
Objects : Highlights of the Deep Sky”, Pub.
Cambridge University Press p.193 (2008)
NGC 2437 / M46 / H IV 39 / h.464 /
C*0739-147 / OCl 601 (07417-1449) [U274/U275] is the open
star cluster.
Open Cluster Descriptions
Steve Coe, using 32cm. 13.1-inch f/5.6 describes;
“NGC 2437 (M 46) Very bright, very
large, rich, somewhat compressed, I estimated 140 stars by
counting 35 stars in the northeast quadrant. The cluster in
obvious in the 11×80 finder and can be seen naked eye
at most of the observing sites in Arizona.
“Sentinel 13-inch
7/10—11×80 immediately obvious, 4 stars
resolved, a smooth cluster, 150× very bright, very
large, compressed, round, 116 stars counted, many beautiful
chains. Planetary on north edge is obvious, light green
with central star.”
“RFT 6−inch f/6 Sun Valley
7/10 S+T Both M 46 and M 47 fit in the same field of view
with 38mm Giant Erfle EP. Even at this very low power
(30×), M 46 shows up like a rich grouping with many
pretty faint stars. Using the 14mm EP resolves 68 stars
in a very bright, very large, compressed and very rich
cluster.”
Surrounding Fields
M47 / NGC 2422 / ()....
Observational Descriptions of M47
Steve Coe writes on the open star cluster as;
“…Very bright, very large,
not compressed, scattered group with several bright stars
of 8th magnitude and more to fill in the background, 44
stars counted at 100×. This nice cluster is an easy,
obvious cluster in the 11×80 finder, there are several
stars resolved and a lovely orange star, KQ Pup, is about
30 arcmin west of the cluster at low power. Struve 1121
is a double star near the center of M-47, it is a mag
7/7.5 pair, sep 7″, it is easily split at 100×.
On an 8/10 night during the Messier Marathon, the 13-inch
resolved 85 stars from mags 8 on down. This great cluster
shows a bizarre round section in the center with NO stars,
strange to see some many cluster stars and none in the
center, even on an excellent night.”
RFT 6-inch f/6 “very large, pretty
rich, not compressed, 24 stars counted with 38mm EP. A
wide, dark lane separates the 2 lines of stars. With the
14mm EP 38 stars are counted and William Herschel’s
description of “st L & S” for
“stars large and small” is obvious. This
cluster is indeed a mix of stars magnitudes 8 and 9 then a
jump to stars of 11th mag and fainter.”
Last Update : 04th November 2011
Southern Astronomical Delights ©
(2011)
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