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Index charts to the 50 plates of Barnard's dark cloud atlas



 
 
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  #1  
Old August 8th 05, 05:08 AM
canopus56
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Default Index charts to the 50 plates of Barnard's dark cloud atlas

This is to announce a preliminary release of index charts to aid in
using Plates and Charts 1-50 (omitting Plates 27 and 51) in Edward
Emerson Barnard's "A Photographic Atlas of Selected Regions of the
Milky Way" (1927) ("Barnard's Atlas"). Barnard's Atlas features
pictures taken with the 1910's state-of-the-art 10" Bruce Telescope.
The Atlas was intended to introduce the public to beauty of the Milky
Way and to provide a post-humus final version of Barnard's catalogue of
dark clouds.

These index charts plot the epoch J2000 boundaries of the epoch B1875
photographs in Volume I and in the annotated charts in Volume II of
Barnard's Atlas. For example, the reader can use the following index
chart for the Aquila area -

http://members.csolutions.net/fisher...dcc_aql7_1.gif

- to orient Plates 34 through 42 to the night sky.

These index charts are intended to be used in conjunction with a recent
internet distribution of Barnard's Atlas by the Georgia Institute of
Technology ("GIA").
http://www.library.gatech.edu/about_...ard/index.html

The GIA distribution of Barnard's Atlas offers PDF downloads that
compile in one file for each plate:
1) Barnard's photograph from Volume I of the Atlas.
2) Barnard's narrative on the plate.
3) Mary R. Calvert's annotated line-drawing chart showing the
outlines of the objects in Barnard's catalogue from Volume II of the
Atlas.
4) A digital overlay of Calvert's annotated chart over Barnard's
photograph.

Calvert's line drawings represent the definitive statement of the
boundaries that Barnard intended for each dark cloud in his catalogue.
Calvert's line drawings annotate the boundaries of distinct (solid
line) and indistinct (dotted line) dark nebulae and reflective regions
("nebulosity" in Barnard's Atlas). The following excerpt from Chart 42
illustrates the three types of plotted lines -

http://members.csolutions.net/fisher...t44gamCygExce=
rpt.jpg

Calvert's line charts give much more descriptive information on the
catalogue object than Barnard's catalogue. A typical note to Barnard's
catalogue provides little useful content, as illustrated by the note to
Barnard Object No. 3: "Irregular, dark space in nebula; curved, bright
strip of nebulosity in SW." Other chart alternatives, like Sky 2000
and Uranometria 2000, chart the Barnard objects, but often combine
outlines of several objects into one boundary.

The index charts to the plates in Barnard's Atlas can be downloaded as
follows. The numbers in parentheses list the Barnard Atlas plates
plotted on the index chart:

East Sgr (28-31) and East Sco (19-22) Groups to mag 7.1 and 7.6

http://members.csolutions.net/fisher..._sgre_scoe7_1=
..gif


http://members.csolutions.net/fisher..._sgre_scoe7_6=
..gif


West Sgr (23-26) and West Sco (11-18) Groups to mag 7.1 and 7.6

http://members.csolutions.net/fisher..._sgrs_scow7_1=
..gif


http://members.csolutions.net/fisher..._sgrs_scow7_6=
..gif


Aql-Sct (34-41) Group to mag 7.1 and 7.6

http://members.csolutions.net/fisher...dcc_aql7_1.gif


http://members.csolutions.net/fisher...dcc_aql7_6.gif


Cyg-Cep (43-50) Group to mag 7.1 and 7.6

http://members.csolutions.net/fisher..._cygcep7_1.gif


http://members.csolutions.net/fisher..._cygcep7_6.gif


Per-Cas (1-2) Group to mag 7.6

http://members.csolutions.net/fisher..._Per_dblclust=
er.gif


Per-Aur-Ori (3-9) Group to mag 7.1 and 7.6

http://members.csolutions.net/fisher..._oriper7_1.gif


http://members.csolutions.net/fisher..._oriper7_6.gif


CMa (10) Group to mag 8.5

http://members.csolutions.net/fisher..._CMa8_5_FOV13=
..gif


The J2000 Barnard plate boundaries are also distributed here in three
parts as Cartes du Ciel external nebula catalogues.
http://members.csolutions.net/fisher.../bdcc/bdcc.zip


The Cartes du Ciel compatible nebula catalogues divide the 50 plates
into three groups:
1) All plates outside of the Sagittarius-Scorpius region (files
bdc1.hdr, *.dat and *.txt).
2) The west groups of the Sagittarius-Scorpius region (files
bdc2.hdr, *.dat and *.txt). See
http://members.csolutions.net/fisher..._sgre_scoe7_1=
..gif

3) The east groups of the Sagittarius-Scorpius region (files
bdc3.hdr, *.dat and *.txt). See
http://members.csolutions.net/fisher..._sgre_scow7_1=
..gif


The reason for dividing the Sagittarius-Scorpius region into two parts
is there are so many overlapping plates covering this region. Including
them in one plot catalogue generates a confusing, difficult to
interpret display. E.g. -

http://members.csolutions.net/fisher...c_confused.gif

The Sagittarius-Scorpio region includes the Milky Way galactic core and
local Sagittarius-Ophiuchus dark clouds.

Using an existing Barnard Dark Object catalogue for Cartes du Ciel
http://www.stargazing.net/astropc/external.html , it is now
possible to plot Barnard object locations and the Barnard Atlas plate
boundaries that surround those objects. Together with Cavert's charts
in Volume II of the Atlas, the amount of effort that amateur observers
need to expend to confirm the location and shape of Barnard dark cloud
can be greatly reduced.

Another useful featured provided by these index charts is the
identification of the location of bright stars in Calvert's line charts
and Barnard's star catalogue tables for each plate by Bayer and
Flamsteed numbers. Calvert's annotated charts in Volume II of the
Atlas only list stars by a three digit catalogue number. Common stars
like Deneb might be identified by only a number like "832". The Aquila
area index chart presented above also plots, using Cartes du Ciel, the
boundaries of the Barnard plates with Bayer and Flamsteed numbers for
bright stars. These index charts aid in rapidly locating the
corresponding bright stars in Calvert's line charts and in Barnard's
charts and tables.

The following objects in Barnard's catalogue of 349 dark clouds do not
appear on plates 1-50 of Barnard's Atlas: 6, 7, 8, 9, 12, 13, 16, 17,
18, 19, 25, 26, 27, 28, 29, 33, 37, 39, 140, 155, 158, 159, 162, 168,
175, 222, 230, 315. In Cartes du Ciel, these objects plot outside the
boundaries of any plate in Barnard's Atlas. Two Barnard Atlas plates,
nos. 2 and 42, contain no Barnard objects.

The epoch J2000 boundaries of the Barnard Atlas plates were generated
by making a table of crude, low precision B1875 coordinate take-offs
from Barnard's Atlas.

http://members.csolutions.net/fisher...ersB1875TakeO=
ffs.htm

As noted in the introduction to Volume II of the Atlas, prepared after
Barnard's death: "A high degree of accuracy is not claimed for these
charts, but they are sufficiently precise to locate and object closely
enough for identification in a catalogue." Using Meuss's low-precision
precession formula, the B1875 coordinates were translated to J2000
coordinates.

http://members.csolutions.net/fisher...rnersJ2000.htm

Nutation has not been applied. The resulting coordinates were ported
to Cartes du Ciel compatible nebula outline files.

Once plotted in Ciel, each of the 49 plates (1-50, omitting Plate 27)
in Ciel were inspected and compared for orientation and boundaries to
the plates in the Atlas and Barnard's star catalogue of each plate in
Volume II of the Atlas. It was felt that Ciel plots represented the
boundaries of the Barnard Atlas plates sufficiently for their intended
purpose: 1) to rapidly orient an Atlas plate to the night sky and 2) to
rapidly locate three bright stars and/or Messier objects located on
Calvert's line charts and Barnard's star catalogue table for that
plate.

A single object test of the precession formula on Barnard 43 confirms
the low-precision accuracy of the precession formula used here to
transform epoch B1875 coordinates to J2000:

Barnard 43 in B1875 per VizieR catalogue VII/220A/barnard
B1875 16h 23m 00s -19.5d

CDS Simbad FK5/J2000 coordinates for B43:
16h 29.9m -19d 36m

Georgia Institute of Technology J2000 coordinates for B43:
16h 29m 7s -18d 50m

J2000 Precession formula used he
16h 30m 44.50s -19d 46m 14.5s

It is hoped that these index charts to the plates and charts in
Barnard's Atlas will increase the enjoyment of amateurs discovering
this overlooked class of difficult objects. A common problem
encountered when first observing dark nebulae is "Are you looking at
the right object?" For dark objects, this questions is more vexing
than when looking at typical light-emitting objects. Dark objects have
even less contrast than against the background night sky than dim
stars. Barnard (1919) cautioned that "It would be unwise to assume
that the dark places shown on photographs of the sky are due to
intervening opaque masses between us and the stars." I have always had
difficulty in understanding exactly what each Barnard objects consists,
given only commonly available coordinates and Barnard's tabular notes
by object number.

Calvert's line drawing charts (now distributed over the internet by the
Georgia Technical Institute) present the definitive statement on what
Barnard intended the boundaries of each object to be. But even
Calvert's charts can be difficult to use. It is hoped that the index
charts and Cartes du Ciel compatible external nebula databases will
remove some of these barriers to identifying the Barnard clouds and
will allow more amateurs to enjoy this interesting class of night sky
objects.

Future enhancements will expand Barnard's catalogue with the
corresponding opacity and positions of objects in Lynds' "Catalogue of
Dark Nebula" (1962) and the known distances to selected Lynd-Barnard
dark clouds in Hilton's "Distance measurements of Lynds galactic dark
nebulae" (1995).

Send comments and corrections to .

- Enjoy - Canopus56

Acknowledgements: These index charts and Cartes du Ciel compatible
catalogues make use of catalogues and data from the VizieR service of
the Centre de Donn=E9es astronomiques de Strasbourg, France.

Charts distributed here were generated using Cartes du Ciel.
http://www.stargazing.net/astropc/ .

This amateur-observer-author is not affiliated with the Georgia
Institute of Technology or Cartes du Ciel.

References:

Barnard, E.E. 1919. On the dark markings of the sky, with a catalogue
of 182 such objects. Astrophys. J., 49:1-24 (1919) NASA ADS link:
http://cdsads.u-strasbg.fr/cgi-bin/n...pJ....49....1B

Barnard, E.E. 1927. A Photographic Atlas of Selected Regions of the
Milky Way. Carnegie Institution of Washington.
http://www.library.gatech.edu/about_...ard/index.html ;
also available in hardcopy from ProQuest UMI Books on Demand.
http://wwwlib.umi.com/bod (BOD catalogue nos. WB1-2050305-060 and
WB1-2050305-061)

Barnard, E.E. 1927. Barnard's Catalogue of 349 Dark Objects in the
Sky. CDS VizieR catalogue VII/220A/barnard and VII/220A/notes.
http://vizier.u-strasbg.fr/viz-bin/Cat?VII/220A . The catalogues can
be queried through the CDS VizieR gateway at
http://vizier.u-strasbg.fr/viz-bin/V...rce=3DVII/220A ; Cartes
du Ciel compatible build
http://www.stargazing.net/astropc/external.html

Hilton J., Lahulla J.F. 1995. Distance measurements of Lynds galactic
dark nebulae. CDS VizieR catalogue J/A+AS/113/325/table1a and table1b.
http://vizier.cfa.harvard.edu/viz-bi...A%2bAS/113/325

Lynds, Beverly T. 1962. Catalogue of Dark Nebulae. Astrophys. J.,
Supp. 7, 1 NASA ADS Link:
http://cdsads.u-strasbg.fr/cgi-bin/n...pJS....7....1L

Meeus, Jan. 1999. (2d) Astronomical Algorithms. Willman-Bell.
http://www.willbell.com/math/mc1.htm

  #2  
Old August 8th 05, 02:18 PM
William Hamblen
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On 7 Aug 2005 21:08:50 -0700, "canopus56" wrote:

3) Mary R. Calvert's annotated line-drawing chart showing the
outlines of the objects in Barnard's catalogue from Volume II of the
Atlas.


BTW, Mary Calvert = Mrs. Barnard.

  #3  
Old August 8th 05, 07:26 PM
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A common problem
encountered when first observing dark nebulae is "Are you looking at
the right object?" For dark objects, this questions is more vexing
than when looking at typical light-emitting objects. Dark objects have
even less contrast than against the background night sky than dim
stars.


I have never understood how a visual observer could claim to "see" a
dark nebula. If all you are seeing is an absence of stars, then you
might as well be looking at some star-poor region of the sky, and any
attempt to observe a dark nebula will automatically be successful.

If the dark nebula is instead delineated by it bordering against a
bright nebula, then the observer is "seeing" the bright nebula rather
than the dark nebula.

For those who claim to have "seen" dark nebulae, what is it that
constitutes a successful or unsuccessful attempt?

  #4  
Old August 8th 05, 10:20 PM
canopus56
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wrote:
I have never understood how a visual observer could claim to "see" a
dark nebula. . . . If the dark nebula is instead delineated by it
bordering against a bright nebula, then the observer is "seeing"
the bright nebula rather than the dark nebula. snip


The basic criteria for visual "seeing" is that the object can be
perceived and distinguished from it's surrounding. "Seeing" is not
limited to bright objects that emit or reflect photons that eventually
strike your retina. It is the ability to detect a physical object that
controls.

To use an analogy, in a Bortle 2 true dark class sky, terrestrial water
vapor clouds are visible only as dark outlines. ("Any clouds in the sky
are visible only as dark holes or voids in the starry background.") In
a Bortle 3 class rural sky, terrestrial water vapor clouds are visible
by their reflection of ambient light pollution. ("Clouds may appear
faintly illuminated in the brightest parts of the sky near the horizon
but are dark overhead.")

Neither means of "seeing" a terrestrial water vapor cloud detracts from
the fact that you are "detecting" a physical object. The point is you
can detect the object sufficiently to appreciate it and that you have a
reasonable assurance that you are looking at the right object.

Your question poses the basic dilemma for visual observers of dark
celestial objects: How to distinguish between seeing legitimate
physical objects and merely dark areas in the night sky that have an
absence of light due to the absence of objects? Barnard (1907, 1910,
1913 and 1916) also struggled with this basic problem, using in part
the Horsehead Nebula (Barnard 1913) as a test case.

In Lynds 1962 catalogue, she approached the problem by using the 200
inch Palomar telescope to measure the average brightness of nearby
areas of the sky and comparing them to the average brightness of a
suspect cloud area. Based on those differences she assigned a visual
"opacity" number between 1 to 6. Subsequent, infra-red spectrum and CO
radio emission mapping confirmed the basic structure of molecular gas
found in Lynd's 1962 visual study and that all but a couple of the
Barnard clouds have a physical existence.

In his technologically earlier time, Barnard approached the problem
more informally, apparently using subjective extinguishment of stars
behind a dark cloud and "nebulosity" around images of adjacent stellar
point objects as supplemental criteria. The basic problem of how to
distinguish between a true dark cloud and an area that simply has an
absence of stars is probably why Barnard's 1919 designation of dark
objects is much more conservative than Lynd's 1962 designations. For
example, the B78 complex is much more extensive than that marked by
Barnard - as is evident even to child today casually observing the area
with the naked-eye or wide-field binoculars. Barnard just didn't have
the technological tools to make a reproducible "scientific" declaration
of the extent of many dark objects.

Since the post-Lynd infra-red and radio catalogues confirm the presence
of Lynd-Barnard dark clouds, the Barnard line-drawing charts can be
safely used to distinguish between the two cases of a cloud and a
region with the absence of stars. Lynd's 1-6 opacity scale, along
with common knowledge among amateurs, also is a helpful criterion. My
experience is that Lynd 5 and 6 opacity clouds are the easiest to see
for amateur visual observing. My experience is that at Lynd 4 opacity,
visual detection of clouds becomes more problematic, except for large
areas like B78. Detection of Lynd 4 clouds also depends on the
contrast between the cloud and the average brightness of galactic disk
behind the cloud.

Try some easier high-opacity clouds first. B92 and B93 in M24 are
obvious examples were the background stars in the stellar disk enhance
the features of foregoing molecular cloud, without the cloud emitting
visual energy. See -
http://www.seds.org/messier/more/m024_m2.html
http://www.seds.org/messier/more/m024_b92.html
http://www.seds.org/messier/more/m024_b93.html

The B78 (near theta Ophi) and the Pipe Nebula are another good easy
example, except higher opacity dark clouds stand out as darker regions
in an area of general opacity. Even with (or perhaps best with) small
aperture wide-field binoculars, the dark clouds in Sgr-Ophi region
that obscure the view of the Milky Way's core are evident. Compare -

My index chart to Barnard's Atlas Plates -
http://members.csolutions.net/fisher...rs_scow7_1.gif

Barnard's Chart and Plate 20 regarding B78 at the Georgia Technical
Institute
http://video.library.gatech.edu/cgi-bin/bpdi/bpdi.pl

Alex Mellinger's Milky Way Galaxy photograph -
http://canopus.physik.uni-potsdam.de/~axm/mwpan_vr.html

Mellinger's wide-field close-up of the B78 - Pipe Nebula complex -
http://canopus.physik.uni-potsdam.de...ges/1997-08_14

In conclusion, yes, you generally only "see" the light emissions from
the galactic disk that are brighter than the light absorbing foreground
dark cloud. This defines the boundaries of the cloud. Nonetheless,
dark cloud objects like B92 and 93 have a legitimate beauty and
attraction of their own well-suited for pleasure observing.
Uncertainty in distinguishing between the dark cloud and areas void of
stars may cause many amateurs to shy away from dark cloud observing.
The Calvert charts in Volume II of Barnard's Atlas greatly aid in
reducing that uncertainty.

For those who claim to have "seen" dark nebulae, what is it that
constitutes a successful or unsuccessful attempt?


As to the criterion for sucessful or unsuccessful attempt, IMHO they
are not much different than the basic self-assessment and honesty that
controls "averted vision" detection for light-emitting stars and
extended objects like galaxies. The ability to see both dark and
"light" object depend on sufficient contrast bewteen the object and the
light-polluted background sky; both depend on the light grasp of your
telescope.

One additional constraint for Barnard dark clouds is the absence of a
scale, analogous to stellar magnitudes, that describes how dark the
object is. I hope to address that in the future by distributing a table
that links Lynd's 1-6 opacity scale to the objects in Barnard's
catalogue.

- Canopus56

References:

Barnard, E. E. 1907. On a nebulous groundwork in the constellation
Taurus. ApJ 25:218-225.
NASA ADS Link:
http://adsabs.harvard.edu/cgi-bin/np...pJ....25..218B


Barnard, E. E. 1910. On a great nebulous region and the question of
absorbing matter in space and the transparency of the nebulae. ApJ 31:
8-14
NASA ADS Link:
http://adsabs.harvard.edu/cgi-bin/np...pJ....31....8B


Barnard, E. E. 1913. Dark regions in the sky suggesting an obscuration
of light. ApJ 38:496-501.
NASA ADS Link:
http://adsabs.harvard.edu/cgi-bin/np...pJ....38..496B


Barnard, E.E. 1916. Some Dark Markings on the Sky and What They
Suggest. RASC 10:241-249.
NASA ADS Link:
http://adsabs.harvard.edu/cgi-bin/np...RASC..10..243B
( There is a minor indexing error in the NASA ADS entry. The article starts on page 241, not 243. Use NASA ADS, "GIF" display option to loop back to page 241).


Bortle, John. 2005. The Bortle Dark-Sky Scale.
http://skyandtelescope.com/resources...ticle_81_1.asp accessed
8/2005

  #5  
Old August 9th 05, 04:23 PM
Brian Tung
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Allison Kirkpatrick wrote:
I have never understood how a visual observer could claim to "see" a
dark nebula. If all you are seeing is an absence of stars, then you
might as well be looking at some star-poor region of the sky, and any
attempt to observe a dark nebula will automatically be successful.

If the dark nebula is instead delineated by it bordering against a
bright nebula, then the observer is "seeing" the bright nebula rather
than the dark nebula.


If you see a black square on a white page, are you seeing the black
square, or are you seeing a white page with a square-shaped obstruction
in it? There's obviously no objective difference between the two.
It's a matter of interpretation, and I suspect most people would say
they saw a black square, even if not a single photon so much as leapt
up out of the square into the eyes. Even if the whiteness of the page
were not inherent, but were drawn on the page, pointilistically, I
still think most people would say they saw a black square.

The difficulty with dark nebulae arises because not because they are
the "photo negative" of bright nebulae, I don't think, but because they
have indistinct edges, unlike a black square on a white page, and
because the white dots of the stars are so much further apart. The
principle is the same, though; it's only the practice of detection that
is the tricky part.

What Herschel and others eventually discovered is that from a
statistical perspective, they can't just be star-poor regions of the
sky. It's theoretically possible that in the midst of a 400 mag-10 and
up stars per square degree region of the sky, you could have a hole a
degree across with only four stars that bright in it, but it's pretty
darned unlikely. Assume a Poisson (random) distribution and figure out
the odds.

If there are dark nebulae that are superimposed on already star-poor
regions, you probably wouldn't be able to see them unless you could
see very dim stars through the telescope, which would give a richer
background to discern the nebula. A smaller telescope wouldn't be able
to pick these out.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
  #6  
Old August 9th 05, 05:57 PM
canopus56
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Brian Tung wrote:
If there are dark nebulae that are superimposed on already star-poor
regions, you probably wouldn't be able to see them unless you could
see very dim stars through the telescope, which would give a richer
background to discern the nebula. A smaller telescope wouldn't be able
to pick these out.


Since Barnard was working with 10" aperature astrophotography and the
catalogue lists nothing analogous to a magnitude (perhaps a contrast
index?), my current interest is which Barnard objects are visual and
which require astrophotography to bring out the contrast you describe.
The Tau-Per cloud is an example of region where an obscuring object is
visually detected by being an unusually star poor region.

- Canopus56

  #7  
Old August 9th 05, 09:46 PM
Brian Tung
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Kurt (canopus56) wrote:
Since Barnard was working with 10" aperature astrophotography and the
catalogue lists nothing analogous to a magnitude (perhaps a contrast
index?), my current interest is which Barnard objects are visual and
which require astrophotography to bring out the contrast you describe.
The Tau-Per cloud is an example of region where an obscuring object is
visually detected by being an unusually star poor region.


Barnard's catalogue contains no magnitude because there can't be one.
At best, one could list the extinction. But that wouldn't necessarily
tell you how well the object stands out from the background, because
it depends on the background.

Do those dark nebulae glow prominently enough in other wavelengths?

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
  #8  
Old August 9th 05, 11:56 PM
canopus56
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Brian Tung wrote:

Barnard's catalogue contains no magnitude because there can't be one.
At best, one could list the extinction. But that wouldn't necessarily
tell you how well the object stands out from the background, because
it depends on the background.


I hope to address that in the future by distributing a table that links
Lynd's 1-6 opacity scale to the objects in Barnard's catalogue. Such a
table will not address the key point of background contrast.
Unfortunately, I am having problems replicating some the associations
that Lynds made in Table 2 of her original 1962 paper between Lynds ID
nos and Barnard ID nos. About ten of Lynds ID nos. are more than 5
degrees away from the corresponding J2000 position in Barnard's
catalogue - making the association suspect.

My abilities and resources are not up to link Barnard ID nos with the
IRAS or Dames's CO databases - which are based on non-visual emissions
rather than visual opacity. Informally, Lynd's opacity seems to work
for pleasure observing purposes.

- Canopus56

 




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