Herschel-400 list -- brighter than you think (LONG)
Jay Reynolds Freeman
by Jay Freeman, April 1999
Several people have privately expressed admiration or disbelief of
my observation of the entire Herschel-400 list in a 55 mm refractor,
reported on p. 114 of the May, 1999 issue of _Sky_&_Telescope_. I
welcome skepticism, but I do not think praise is warranted. I paid
little attention to published magnitudes of the objects during my
survey, for the target was a specific list, not a magnitude limit. Yet
I did not and do not believe that the faintest objects on the
Herschel-400 list are as difficult as commonly perceived.
I have informally known for a long time that many older cataloged
magnitudes of deep-sky objects systematically underestimate their
brightness to the visual observer -- the fact that many magnitudes were
obtained in blue wavelengths guarantees that result, for many kinds of
deep-sky objects are intrinsically brighter in the visual than in the
blue, and reddening by interstellar dust creates an additional
brightness difference, favoring visual wavelengths over blue, for
objects near the plane of the Milky Way. To quantify these effects, I
decided to look up recent visual magnitudes for at least the fainter
objects on the Herschel-400 list.
I downloaded the official Herschel-400 list from the web site of the
Astronomical League (AL) on April 3, 1999, from the URL
http://www.astroleague.org/al/obsclubs/herschel/h400lstn.html
The magnitudes given by the Astronomical League are asserted to be
visual ones, though rather old. I investigated objects for which a
magnitude 12.5 or fainter was given, as well as those for which no
magnitude was provided. (The latter are indicated by "0.0" for the
Astronomical League's magnitude.) That gave me 72 objects in all, 18
percent of the list. I looked up their visual magnitudes in more recent
catalogs (see footnotes), and have tabulated the results in Table 1.
I found visual magnitudes for 57 of the 72 objects. The faintest
was 12.32, for NGC 4085, and only one other object, NGC 3395, had a
recent visual magnitude fainter than 12.0. Some of the objects for
which I found no visual magnitude are galaxies with blue magnitudes
faint enough to suggest that their visual magnitudes might also exceed
12.0. The faintest such blue magnitude is 13.06, for NGC 3912.
The faintest Herschel-400 object, according to the Astronomical
League's data, is NGC 6540, with visual magnitude given as 14.5. Other
catalogs suggest this value was obtained in the blue, as further
indicated in the tabulation and footnotes. Brian Skiff (private
communication, April, 1999) suggested that there had been no good
measurement of the visual magnitude of NGC 6540 so far. Given the
position of NGC 6540 in the Sagittarius Milky Way, it would not be
surprising if it were highly reddened, with visual magnitude
significantly brighter than blue, but I shall not speculate on how much.
The second-faintest Herschel-400 object, according to the
Astronomical League's data, is NGC 6369, with a visual magnitude of 14.0
given. A more recent visual magnitude is 11.4. The third- and
fourth-faintest objects, according to the Astronomical League's data,
are the planetary nebulae NGC 1501 and NGC 7008, both with magnitudes
given as 13.5, but with recent visual magnitudes of 11.5 and 10.7
respectively.
I don't think the general nature of these differences is as
well-known as it ought to be. Perhaps because the Astronomical League's
tabulation is commonly used as a reference for magnitudes of the
Herschel 400, that list is often believed to be a difficult challenge,
containing objects beyond magnitude 14. Yet in fact, its faintest
visual magnitudes seem two magnitudes brighter. Other things being
equal, that correction corresponds to a reduction by 60 percent -- a
factor of 2.5 -- in the clear aperture (diameter) required to see all
the objects on the list. Thus visual observers should take heart, for
the Herschel-400 list seems much more accessible to them than is widely
believed.
################
Table 1. Visual magnitudes of 72 Herschel-400 objects, by NGC number.
"AL" magnitudes are from Astronomical League data, "recent" ones
are visual magnitudes from several newer catalogs. The table
includes all H-400 objects with "AL" magnitude 12.5 or fainter,
and all those with no "AL" magnitude. For some entries with no
"recent" magnitudes, I have added blue or photographic magnitudes
as comments. See text and footnotes for citation of sources.
NGC# Type (1) Magnitudes (2) Comments
AL recent
246 PlN ---- 10.9
278 Gal 12.5 10.85
596 Gal 12.5 10.87
615 Gal 12.5 11.5
1022 Gal 12.5 11.44
1501 PlN 13.5 11.5
1535 PlN ---- 9.6
1788 DfN ---- -----
1931 C/N 13.0 11.3
1999 DfN ---- -----
2022 PlN 13.0 11.6
2024 DfN ---- ----- "Flame Nebula" or "Tank Tracks"
2185 DfN ---- -----
2371 PlN 13.0 11.2 for NGC 2371 and 2372 combined
2372 PlN 13.0 see NGC 2371
2392 PlN ---- 9.1
2479 OCl ---- ----- 9.6 (4), 10 (5)
2742 Gal 12.5 11.7
2782 Gal 12.5 11.49
2811 Gal 13.0 11.27
2950 Gal 12.5 10.95
2964 Gal 12.5 11.34
2974 Gal 12.5 10.78
3193 Gal 12.5 10.92
3226 Gal 12.5 11.4
3242 PlN ---- 7.7
3277 Gal 13.0 11.74
3395 Gal 12.5 12.1
3608 Gal 12.5 10.98
3619 Gal 12.5 ----- blue magnitude 12.6 (3)
3655 Gal 13.0 11.64
3665 Gal 12.5 10.76
3729 Gal 13.0 11.38
3813 Gal 13.0 11.72
3900 Gal 12.5 11.38
3912 Gal 13.0 ----- blue magnitude 13.06 (3)
3962 Gal 12.5 10.59
3982 Gal 12.5 ----- blue magnitude 11.74 (3)
4085 Gal 13.0 12.32
4102 Gal 12.5 ----- blue magnitude 12.3 (3)
4143 Gal 12.5 ----- blue magnitude 12.1 (3)
4150 Gal 12.5 11.66
4245 Gal 12.5 11.36
4273 Gal 12.5 11.92
4281 Gal 12.5 11.32
4346 Gal 12.5 ----- blue magnitude 12.18 (3)
4419 Gal 12.5 11.13
4478 Gal 12.5 11.23
4485 Gal 13.0 11.96
4550 Gal 12.5 11.59
4660 Gal 12.5 10.99
4800 Gal 13.0 ----- blue magnitude 12.3 (3)
4845 Gal 12.5 ----- blue magnitude 12.10 (3)
5273 Gal 12.5 11.57
5473 Gal 13.0 11.4
5557 Gal 13.0 11.10
5631 Gal 12.5 ----- blue magnitude 12.50 (3)
5689 Gal 12.5 11.9
5982 Gal 12.5 11.13
6207 Gal 12.5 11.62
6217 Gal 12.5 11.22
6369 PlN 14.0 11.4
6401 GCl ---- 9.5
6426 GCl 12.5 11.20
6445 PlN 13.0 11.2
6517 GCl 13.0 10.3
6540 OCl 14.5 ----- 14.6 (4), 15 (5)
6544 GCl ---- 8.25
6781 PlN 12.5 11.4
7000 DfN ---- ----- North American Nebula
7008 PlN 13.5 10.7
7448 Gal 12.5 11.65
Footnotes:
=========
(1) The abbreviations are: C/N -- cluster with nebula; DfN -- diffuse
nebula; Gal -- galaxy; GCl -- globular cluster; OCl -- open cluster;
PlN -- planetary nebula.
The exact nature of a few of these objects possibly differs from the
types listed, which are as the Astronomical League provided; however,
I shall not address those issues here.
(2) m1: Magnitude provided on the Astronomical League's Herschel 400 web
pages as of 3 April 1999. These data are stated to be visual
magnitudes, though quite old.
m2: Visual magnitude from more recent compilations, generally from
_Sky_Catalog_2000.0_, volume 2, 1985. Alan Hirshfeld and
Roger W. Sinnott, eds. Sky Publishing.
_Sky_Catalog_2000.0_ did not give visual magnitudes for
planetary nebulae, so I obtained those from
_Planetary_Nebulae_, 1991. Steven J. Hynes. Willmann-Bell.
(3) For objects other than planetary nebulae, and for which _Sky_Catalog_
_2000.0_ gave no visual magnitude, I added a blue magnitude from
that same source, if one was given.
(4) The magnitude given is a photographic magnitude provided by
_Sky_Catalog_2000.0_, with wavelength band specified only as
"photographic".
(5) The magnitude given is a photographically determined blue magnitude,
given in _NGC_2000.0_ (1988, Roger W. Sinnott, Sky Publishing). This
source gives photographic blue magnitude values only to the nearest
magnitude.
--
Jay Reynolds Freeman -- freeman at netcom dot com -- I speak only for myself.
Ratboy99
You work too hard.
rat
~( );>
tfla...@my-dejanews.com
fre...@netcom.com (Jay Reynolds Freeman) wrote:
> I did not and do not believe that the faintest objects on the
> Herschel-400 list are as difficult as commonly perceived.
Quite by accident, the first version of the Herschel 400 list that
I stumbled on was at http://www.seds.org/billa/herschel/h400.txt.
Posted by Bill Arnett and attributed to Brenda Branchett of Deltona,
Florida. I don't know where she got her magnitudes from, but they
seem to be in line with the ones you have posted, and they correlate
reasonably well with how hard I find the objects, after correcting
for the surface brightness of galaxies, except that planetary
nebulae seem to be listed by photographic rather than visual
magnitude. Only two objects are listed below mag 12.0: the
planetaries NGC 1501 and NGC 7008, at 13.3 and 13.5 respectively.
Subjectively, most of the Herschel 400 objects are quite easy to
see in my 7-inch Dob under exurban skies, and a fair number are
actually quite bright, including many that are readily visible in
my 10X50 binoculars. After all, this is supposed to be a list
of the 400 best objects, not the 400 hardest objects.
So far, I have found about a dozen to be genuinely challenging -- not
necessarily the ones with the greatest listed magnitudes, either.
Curiously, the hardest ones on my combined list of Herschel 400 objects
and RASC 110 objects are often from the 30 objects that are on the
latter list but not on the former.
- Tony Flanders
Cambridge, MA
-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Bob Smith
I must say that on S.A.A there is a lot of helpful equipment talk and this,
believe me, has been of extreme value to me. I don't know where I'd be
without the help of guys like Todd and others who devote so much of their
time to equipment.
BUT, you sir, stand out amongst all by actually going out and doing
something so extraordinary - showing that good astronomy can be done with
the simplest of equipment made up for with intellect and perseverance. Your
accomplishment will, I know, incent many people to go after the Messier,
Herschel lists, or even start a Variable Star observing program with modest
equipment and they too can say - I did it.
May Refractor Red live on...
Long live Refractor Red
Bob Smith
Atlanta, GA
bsmith at msn dot com
>
>> Herschel-400 list -- brighter than you think
>> by Jay Freeman, April 1999
>>
>> Several people have privately expressed admiration or disbelief of
>>my observation of the entire Herschel-400 list in a 55 mm refractor,
...
Dave
>In article <freeman-not-h...@netcom.com>,
> fre...@netcom.com (Jay Reynolds Freeman) wrote:
>
>> I did not and do not believe that the faintest objects on the
>> Herschel-400 list are as difficult as commonly perceived.
I feel that they are the next observing list to tackle after the
Messier list. They are moderate in difficult but not so hard as to
discourge as well...
>
>Subjectively, most of the Herschel 400 objects are quite easy to
>see in my 7-inch Dob under exurban skies, and a fair number are
>actually quite bright, including many that are readily visible in
>my 10X50 binoculars. After all, this is supposed to be a list
>of the 400 best objects, not the 400 hardest objects.
I have seen all in a 8 inch Dob myself. :)
Now the next 400 was a lot harder :)
Come and visit Dave's Astronomy Page at
http://www.ccse.net/~davidc2/
Dave from Jacksonville
I am Homer of Borg you will assim.....OHH DONUTS!!!!
Herschel 400 Certificate #146, Herschel II Certificate #6
dave_...@my-dejanews.com
> by Jay Freeman, April 1999
>
> Several people have privately expressed admiration or disbelief of
> my observation of the entire Herschel-400 list in a 55 mm refractor,
> reported on p. 114 of the May, 1999 issue of _Sky_&_Telescope_. I
> welcome skepticism, but I do not think praise is warranted. I paid
> little attention to published magnitudes of the objects during my
> survey, for the target was a specific list, not a magnitude limit. Yet
> I did not and do not believe that the faintest objects on the
> Herschel-400 list are as difficult as commonly perceived.
snip
Jay,
Are you aware that the listed magnitudes in the AL "Observe the Herschel 400
Objects" handbook (title?) are more in line with your recent magnitude
fiqures? In fact, in some cases, e.g. NGC 246 and NGC 1931, they are
considerably lower.
Some of the galaxies on the Herschel 400 list that are in the 11th magnitude
range (handbook) have been extremely difficult for me to positively log. For
example, I have been unable to see NGC 6118 (mag 11.5) in Serpens Caput from
two different sites in south central Pennsylvania using 17 and 20" classical
Cassegrain reflectors. Under the dark Vermont skies of the Stellafane
convention I was able to bag this elusive galaxy with an 8" Newtonian
reflector. On Monday night I searched in vain for another difficult galaxy,
NGC 2613 (mag 11.0) in Pyxis using the 17" classical Cassegrain. I had no
trouble finding NGC 2811 (mag 11.7) in Hydra. NGC 2974 (mag 11.0) in Sextans
proved to be more difficult.
It just shows to go you that listed magnitudes should be taken with a grain of
NaCl. :-)
Dave Mitsky
ASH, DVAA
Wouter van Reeven
> Some of the galaxies on the Herschel 400 list that are in the 11th magnitude
> range (handbook) have been extremely difficult for me to positively log. For
> example, I have been unable to see NGC 6118 (mag 11.5) in Serpens Caput from
> two different sites in south central Pennsylvania using 17 and 20" classical
> Cassegrain reflectors. Under the dark Vermont skies of the Stellafane
> convention I was able to bag this elusive galaxy with an 8" Newtonian
> reflector. On Monday night I searched in vain for another difficult galaxy,
> NGC 2613 (mag 11.0) in Pyxis using the 17" classical Cassegrain. I had no
> trouble finding NGC 2811 (mag 11.7) in Hydra. NGC 2974 (mag 11.0) in Sextans
> proved to be more difficult.
>
> It just shows to go you that listed magnitudes should be taken with a grain of
> NaCl. :-)
The way a deep-sky object appears in the eye-piece not only depends on
the total amount of light it emits (or the total magnitude) but also the
surface brightness.
According to "The Deepsky Field Guide to U2000" NGC 6118 has a total mag
of m=11.7 while a surface brightness of sb=13.9.
The three galaxies you compare have these numbers :
NGC 2613 m=10.5 sb=13.2
NGC 2811 m=11.3 sb=11.3
NGC 2974 m=10.9 sb=12.5
So you see that the ones with the lowest sb are most difficult to see.
Wouter van Reeven
--
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
| Alone in the clouds all blue... |
| |
| * |
| '* * * |
| * * |
| * |
| |
| Clear skies! |
| Wouter 'Teus' van Reeven |
| Ree...@Strw.LeidenUniv.Nl |
| http://www.strw.leidenuniv.nl/~reeven/ |
| icq 34696027 |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Lumpy Darkness
: According to "The Deepsky Field Guide to U2000" NGC 6118 has a total mag
: of m=11.7 while a surface brightness of sb=13.9.
: The three galaxies you compare have these numbers :
: NGC 2613 m=10.5 sb=13.2
: NGC 2811 m=11.3 sb=11.3
: NGC 2974 m=10.9 sb=12.5
: So you see that the ones with the lowest sb are most difficult to see.
Well, I'm not so sure it is that simple. Isn't it possible that a galaxy
can have a bright nucleus or fairly birght HII regions that are pretty
easily seen, but the extended portions (being most of the galaxy) are very
dim. That yields a low surface brightness to, doesn't it?
--
-Lumpy Darkness-
Northern California amateur astronomers, check out TAC
The Astronomy Connection at http://www.seds.org/TAC
Jay Reynolds Freeman
> Objects" handbook (title?) are more in line with your recent magnitude
> fiqures? In fact, in some cases, e.g. NGC 246 and NGC 1931, they are
> considerably lower.
Glad to hear it, but no, the only AL data I have used for the H400 is
the material on their web site.
> Some of the galaxies on the Herschel 400 list that are in the 11th magnitude
> range (handbook) have been extremely difficult for me to positively log. For
> example, [ ... NGC 6118 ]
I agree, that one is a toughie. I believe you were one of the folks
who first called my attention to it as such, last summer. One thing that
I do have going for me out here in California is high transparency at some
of the sites I use. Several thousand miles of ocean immediately upwind
helps with that, a lot.
tfla...@my-dejanews.com
dav...@mediaone.net (Dave) wrote:
> I feel that [the Herschel 400 is] the next observing list to tackle after
> the Messier list. They are moderate in difficult but not so hard as to
> discourge as well...
As I near the completion of both the Herschel 400 and the RASC 110, I would
have to disagree with this statement. All in all, I think that the RASC 110
is a better-selected list. Not surprising; it is easier to make a list of
110 good objects than 400 good objects. Also, the RASC 110 was not
constrained by having to stick to things that William Herschel found. Great
as he was, he did miss some fine objects. However, I would *not* recommend
attacking the RASC 110 without a nebula filter. Herschel, of course, didn't
have one of those ...
- Tony Flanders
Cambridge, MA
-----------== Posted via Deja News, The Discussion Network ==----------
Wouter van Reeven
>
> Wouter van Reeven said. . . :
>
> : According to "The Deepsky Field Guide to U2000" NGC 6118 has a total mag
> : of m=11.7 while a surface brightness of sb=13.9.
> : The three galaxies you compare have these numbers :
>
> : NGC 2613 m=10.5 sb=13.2
> : NGC 2811 m=11.3 sb=11.3
> : NGC 2974 m=10.9 sb=12.5
>
> : So you see that the ones with the lowest sb are most difficult to see.
>
> Well, I'm not so sure it is that simple. Isn't it possible that a galaxy
> can have a bright nucleus or fairly birght HII regions that are pretty
> easily seen, but the extended portions (being most of the galaxy) are very
> dim. That yields a low surface brightness to, doesn't it?
>
True. The Uranometria 2000 gives this definition of surface brightness :
V'_25 = V_T + delta(V) + 5log(D) - 2.5log(D/d) - 0.26, with
V_T the total V magnitude
delta(V) = 0.25 for cD or E-type galaxies
delta(V) = 0.13 for SO-type galaxies
delta(V) = 0.11 for all other type galaxies
D = major axis in arcminutes
d = minor axis in arcminutes.
D and D are measured for the B_25 isophote, that is the isophote where
the surface brightness in the B magnitude is SB_B = 25.
So the biggest part of the galaxy should be invisible for amateur
telescopes. The surface brightness calculated this way is the MEAN
surface brightness. It's very safe to assume that there are parts of the
galaxy which have a SB higher than the one stated in the table, for
instance the nucleus and some bright HII-regions.
However, the total magnitude and the SB together give a good impression
of what to expect of a galaxy. Experience has taught me that low-SB
galaxies are more difficult to see than high-SB galaxies. I have mostly
observed with a small telescope (6" Newtonian), so if any bright
HII-regions are present in a galaxy I wouldn't see them. But I do have
some experience with bigger telescopes (20" and even a 40" in the south
of France) and still, low-SB galaxies, despite bright HII-regions might
exist, are difficult objects to observe. The eye catches a large fuzzy
path more easily than a few barely visible spots and then the SB is an
important factor.
But I have to admit that some galaxies, despite low SB, are more easily
seen that some other galaxies with higher SB. I only meant to say that
the total magnitude in combination with the SB give good hints on what
to expect.
Dave
>In article <37093757...@news.newsguy.com>,
> dav...@mediaone.net (Dave) wrote:
>
>> I feel that [the Herschel 400 is] the next observing list to tackle after
>> the Messier list. They are moderate in difficult but not so hard as to
>> discourge as well...
>
>As I near the completion of both the Herschel 400 and the RASC 110, I would
>have to disagree with this statement. All in all, I think that the RASC 110
>is a better-selected list.
Where can I find the RASC list? That sounds interesting...
Dave
Jim
>tfla...@my-dejanews.com wrote:
>
>>In article <37093757...@news.newsguy.com>,
>>
>>As I near the completion of both the Herschel 400 and the RASC 110, I would
>>have to disagree with this statement. All in all, I think that the RASC 110
>>is a better-selected list.
>
>Where can I find the RASC list? That sounds interesting...
Ditto. And what is the RASC 110?? Is this a list of 110 non-Messiers
put out by the Royal Astronomical Society of Canada?
(Hey, it's a guess.)
Thanks
Jim
--
There are also heavenly bodies and there are earthly bodies; but the
splendor of the heavenly bodies is one kind, and the splendor of the
earthly bodies is another. The sun has one kind of splendor, the moon
another and the stars another; and star differs from star in splendor.
1 Corinthians 15
Dave
wrote:
>
>Ditto. And what is the RASC 110?? Is this a list of 110 non-Messiers
>put out by the Royal Astronomical Society of Canada?
>(Hey, it's a guess.)
And it was a good guess. I was emailed where I could get the list and
here is the address:
http://www.seds.org/messier/xtra/similar/rasc-ngc.html
Come and visit Dave's Astronomy Page at
http://www.ccse.net/~davidc2/
Dave from Jacksonville
I am Homer of Borg you will be assim.....OHH DONUTS!!!!
David W. Knisely
> >Where can I find the RASC list? That sounds interesting...
>
> put out by the Royal Astronomical Society of Canada?
> (Hey, it's a guess.)
>
>
OBJECTS" in each edition of the RASC Observer's handbook (on page 259 of
this year's edition). This might be the list which was mentioned, and
is a fine group of objects for an observing program intermediate to the
Herschel 400. Also in the Observer's Handbook is a list of 45 "DEEP-SKY
CHALLENGE OBJECTS" intended for scope in the 8 inch to 18 inch range.
The lists like the Messier, RASC, or Herschel 400's are good ways to
motivate a person to get out regularly to observe in a somewhat
structured program. Doing these programs will make a person a better
observer, sharpening their object locating and observing skills (its
also nice to have the certificates on the wall :-)).
I have my own "interesting" list which I put together of objects which
I consider to be worthy of a good look in many amateur scopes. I used
this listing in an old Peachtext List Manager database as source
material for writing my monthly observing reports for my club several
years ago, and I add to it from time to time (it currently has about 314
objects on it). It included the Messiers, the best of the Herschel's,
and a few other NGC/IC or other objects which are often pretty, or at
the very least will tend to show at least some detail (or which are well
known, like the Horsehead for example). I am currently slugging my way
through the Herschel II list now, and it is more of a challenge to my
observing skills than just a listing of pretty targets for star
parties. However, it is serving its true purpose (ie: it makes me get
out under the stars). Each person might just have to decide on their
own what they want to look for, so they can either make up their own
listing, or use the established program listings. What matters is that
a person get out and REGULARLY observe the sky. Those who don't do this
are missing out on the biggest aspect of our hobby. Clear Skies to you
from A.L. Messier Award #224, and Herschel Club Award #12 :-).
--
David Knisely KA0CZC dk8...@navix.net
Prairie Astronomy Club, Inc. http://www.4w.com/pac
Hyde Memorial Observatory, http://www.blackstarpress.com/arin/hyde
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