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Hello, the faintest star I have glimpsed is around 15.5-16 in my 12", and about the same with my 16", has anyone gone any fainter, say magnitude 17.5 and downwards...thanks...clear skies...

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In my 10 inch Newtonian, I have gone into the mid 15's. The scope has shown the central star in M57 and that one is around 15.1 to maybe 15.2. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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3 months back, I was able to glimpse a 15.1 magnitude star with my 4.7" refractor near M97. I have to say one can go down to mid 15's with a 5" under dark skies and high altitude.

/Jake

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I have heard of people go to around 14th magnitude in a 6 inch, but not quite as faint as 15.1, even under pristinely dark conditions. I prefer using photometrically calibrated star fields for limiting magnitude determinations rather than relying on some of the computerized star atlas programs and their magnitudes. Towards the faint end, some of their catalogs (like the Hubble Guide Star Catalog) can be as much as a full magnitude off of the actual visual magnitude. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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3 months back, I was able to glimpse a 15.1 magnitude star with my 4.7" refractor near M97. I have to say one can go down to mid 15's with a 5" under dark skies and high altitude.

/Jake

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I have heard of people go to around 14th magnitude in a 6 inch, but not quite as faint as 15.1, even under pristinely dark conditions. [snip]

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I don't know, Dave. 13.8 magnitude Pluto's been detected in a 70 mm aperture so, 14th magnitude would be a pretty conservative limit for a 150 mm (6 inch) aperture. If you review Schaefer's paper on telescopic limiting mags, many observers reported detections in the low- to mid-14's, with two exceeding 15th magnitude and Skiff going to 15.58 using 6 inch scopes.

When going after the central star in the Ring Nebula, I've detected the 15.7 magnitude star in the adjacent triangular asterism. That was with my old 10 inch, f/4.5 Meade Newtonian, a scope with good but far from great optics. Two observers in the Schaefer paper reported seeing as faint as 16.1 to 16.3 with the same aperture. Frankly, I suspect there's another 0.2 to 0.5 magnitude to be had with that aperture.

I've not tried a limiting magnitude sequence with my 18 inch.

Bill in Flag

--------------------
Grand Canyon Adventure
Lowering the Threshold

18" Obsession
4.5" Meade 4500
10x50 Swift Audubon

Cosmic Voyage

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Hello, the faintest star I have glimpsed is around 15.5-16 in my 12", and about the same with my 16", has anyone gone any fainter, say magnitude 17.5 and downwards...thanks...clear skies...

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In my 10 inch Newtonian, I have gone into the mid 15's. The scope has shown the central star in M57 and that one is around 15.1 to maybe 15.2. Clear skies to you.

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Those Nebraska skies are very nice! I once hosted the Iowa Star Party in "Nebraska".

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3 months back, I was able to glimpse a 15.1 magnitude star with my 4.7" refractor near M97. I have to say one can go down to mid 15's with a 5" under dark skies and high altitude.

/Jake

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I have heard of people go to around 14th magnitude in a 6 inch, but not quite as faint as 15.1, even under pristinely dark conditions. [snip]

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I don't know, Dave. 13.8 magnitude Pluto's been detected in a 70 mm aperture so, 14th magnitude would be a pretty conservative limit for a 150 mm (6 inch) aperture. If you review Schaefer's paper on telescopic limiting mags, many observers reported detections in the low- to mid-14's, with two exceeding 15th magnitude and Skiff going to 15.58 using 6 inch scopes.

When going after the central star in the Ring Nebula, I've detected the 15.7 magnitude star in the adjacent triangular asterism. That was with my old 10 inch, f/4.5 Meade Newtonian, a scope with good but far from great optics. Two observers in the Schaefer paper reported seeing as faint as 16.1 to 16.3 with the same aperture. Frankly, I suspect there's another 0.2 to 0.5 magnitude to be had with that aperture.

I've not tried a limiting magnitude sequence with my 18 inch.

Bill in Flag

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I recall once in 1998 using my variable aperture off-axis stop to stop-down my 10 inch to 3.6 inches (91mm) and managing to just barely glimpse Pluto (magnitude 13.7). I could not see it in any smaller aperture, so that was about as far as I could go. Scaling this up to 4.7 inches would yield a limiting magnitude of 14.1, thus, still a full magnitude short. Using the same scaling for 10 inches would yield a limiting magnitude of about 15.7 for my scope, which is in rough agreement with your results although maybe just a tad fainter than I have actually verified with some calibrated star fields (15.1 to 15.6 typically on a halfway decent night). Clear skies to you.

--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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Scaling this up to 4.7 inches would yield a limiting magnitude of 14.1, thus, still a full magnitude short.

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Again, the magnitudes of the faintest stars in the Hubble Guide Star Catalog are often *very* inaccurate. The observer cannot *and should not use them for magnitude estimates. The Guide Star Catalog is just an engineering product used for pointing the Hubble Space Telescope and not for accurate photometry of stars.

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...the data comes from research and photometry by Brian Skiff, Tom Polakis, and possibly one or two others that may have contributed as well).

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Scaling this up to 4.7 inches would yield a limiting magnitude of 14.1, thus, still a full magnitude short.
/Jake

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And yes, the magnitude 15.1 might not be accurate but it is what Megastar gives and it is the best I can get. The star in question was GSC 3827:466.

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"Never" --

The star you've marked in your drawing of M-97, which you post on your website here...
http://www.kolumbus.fi/jaakko.saloranta/Deepsky/Messier/M97.html
...is indeed the GSC star you've indicated, and my copy of star chart programs gives the same magnitude rating, 15.1. You in fact say on that webpage "Faint star (~mag 15)" which, in fact (as shown below) turns out to be exactly correct.

I use a method that Sue French recommended for determining more accurate visual magnitude ratings: load the Java applet Aladin on the VizieR website, get the field for an object using one of the available surveys (generally I just use POSS I or II) and then overlay the survey NOMAD. It has visual magnitude photometric data for quite a few of the stars down to ~16th mag, as well as R and B magnitudes. Sue seems to consider the Vmag data provided by NOMAD -- when it's available -- to be pretty accurate.

I plotted your star and came up with the NOMAD reference. It is rated at 15.03 visual magnitude: so, it is only *very* slightly brighter than the GSC indicates, certainly not enough to be very noticeable -- likely not visually discernible at all except through instruments.

I don't think you are far off the mark. The screen dump from Aladin is attached.

The star is:

NOMAD1 1450-0213439 NOMAD-identifier
USNO-B1 1450-0207228 Identifier in USNO-B1

RAJ2000 168.5310028 deg Right ascension in ICRS, Ep=J2000
DEJ2000 +55.0522694 deg Declination in ICRS, Ep=J2000

Vmag 15.030 mag

I think it certainly is *possible* to go on and on, arguing this in regard to various survey methods, etc., but the issue is really whether or not you have seen the star. I believe that your sketch is good evidence of this, and certainly the locale of the observation (and your background) would tend to support it. The star IS, as you said, ~15th magnitude; and you say you saw it, how, and where. This seems as satisfactory as the evidence given by any good visual observer, at least to me...

Now, let's look at Lt. Col. Saloranta's bona fides. He doesn't ever seem to give "plugs" about himself but a bit of checking on the Net shows that he writes the monthly deep-sky observing column in the Finnish astronomy magazine "Tähdet ja Avaruus" (Stars & Space), a printed publication whose web URL is here:
http://www.avaruus.fi/

Saloranta also has a huge website containing astronomical observations and drawings of thousands of objects:
http://www.kolumbus.fi/jaakko.saloranta/Deepsky/Astro.html

He regularly observes every year at high altitude sites in Spain, or Greece, or Hawaii, and specializes in using small aperture portable telescopes he can take with him on air flights, having prepared countless drawings with them which I personally find persuasive; for example, here's his drawing of PN Abell 24:
http://www.kolumbus.fi/jaakko.saloranta/Deepsky/Abell/Abell24.html

Saloranta's drawings of open clusters are striking, and when I compare them to DSS images, I'm almost always impressed with their accuracy. Here is his NGC 2354:
http://www.kolumbus.fi/jaakko.saloranta/Deepsky/NGC/NGC2354.html

On his Constellation Index Page --
http://www.kolumbus.fi/jaakko.saloranta/Deepsky/8inch.html
-- Saloranta states at the bottom:
"3223 deep sky (no double stars + limited asterism catalogue) objects listed/observed
1200+ deep sky (since 2001) objects sketched"

So, we're not talking about the 'blunder of a novice' here. I think there are ways to dispute facts and opinions that are positive and constructive, but unfortunately there are also ways that seem to suggest a "GOTCHA!" implication. If the objectors to "Never" in this case do not feel that he has seen the star, it's a matter of conjecture UNLESS they also have done comparable observing at "Las Indias, La Palma, Spain (750m / 2460ft)" with a similar scope, where he made this observation on March 27-8, 2008. Otherwise, it's merely a contest of argument from authority, and you have to reason out from available evidence as to who is most persuasive: the original (highly experienced) claimant, or various objections drawn from entirely different experiments, plus inferences and extrapolations. If Saloranta's assertion is denied ON THE FACE OF IT, even with his given evidence (his drawing), then nobody can be believed, and there is little point for anyone to post visual observations on CN or forums elsewhere.

The skeptic should, if I'm wrong about NOMAD's figure of Vmag for the star, provide alternative references and data. Maybe they'd tend to prove whether it's really "~15th mag" or "15.1" mag, or something entirely different. But then -- as arguments between Roger Clark and Brian Skiff attest in their exchanges on Amastro -- these matters are often very esoteric, and even professional experts can disagree.

Regoma

Edited by Olivier Biot (06/16/08 03:11 PM)

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David,
My copy of this chart goes down to magnitude 19.1, but it has huge gaps below 16.
What's really needed is a field of stars similar to Roger Clark's star cluster sequences in his book "Visual Astronomy of the Deep Sky" that have 0.1mag sequences from 16.5 to 19 for those with larger scopes and darker skies.
M14 would be a good one since its horizontal branch hovers around 17.1 yet has stars from 13.8 to past 20.
So would NGC206, with brightest stars above 17 but lots of stars down to mag.21. Even a 36" could use that.

This can give limiting stellar magnitude, but seems to fall short of giving the observer what he really wants: a clue to how faint a DSO can be seen. There, a combination of total integrated magnitude, surface brightness, and brightness gradient all have to be taken into account to make a realistic appraisal of your chances of seeing something.
I've learned never to take anything for granted, since the actual magnitudes of faint DSOs isn't always perfectly determined. I've had a hard time with some NGC objects, though I have quite a number of UGC, IC, and MCG galaxies in my log. It's gotten to the point where I assume it WILL be visible unless proven otherwise.

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The chart is my own creation, so for my purposes, it was designed to determine how faint one was going in order to see whether it was worth going after the central star in the Ring. As such, I eliminated the photometry of stars fainter than about 16.6, as I had little need to know if I was going fainter (and I doubt I could go that faint with my 10 inch anyway). Clear skies to you.

--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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Taking a quick look at the sketches made from our observing trip... most of the sketches easily show stars fainter than 14.1 magnitude. So seeing like a 15.1 magnitude star with a 4.7" telescope is not impossible but has more like a 10% chance of doing so. This was tested several times during the course of 2 weeks from different sites. On average, at an altitude of 7000ft 14.5 magnitude stars were reported almost constantly visible with an 4.3" aperture.

And yes, the magnitude 15.1 might not be accurate but it is what Megastar gives and it is the best I can get. The star in question was GSC 3827:466.

/Jake

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I would not say that you absolutely couldn't see a 15th magnitude star with a 4.7 inch, but it is unlikely most people can do this on a regular basis with that aperture. I still suspect that the star you saw may be slightly brighter than 15, as the NOMAD photometry uses the YB6 catalog that also relies on scans of photographic plates (Lick Observatory's Northern Proper Motion and the Yale/San Juan Southern Proper Motion programs) rather than photometry of the individual stars. In the picture I provided of the M57 field, the "bright" 13th magnitude star near the Ring I managed to see at least half the time I looked for it in my little 80mm f/5 "short tube" refractor from my dark sky site (ZLM 6.5 to 7.0). This result scaled up to my larger aperture scope suggests that in my 10 inch, I would not be able to go much past 15.6 or so, which is about what I got when I actually did observe the area around M57. I also require that if a star is considered "seen", it must be visible to my eye *at least* 20 percent of the time. This is a bit different from the requirements of a few other observers, but is a pretty consistent level to judge things with. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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And yes, the magnitude 15.1 might not be accurate but it is what Megastar gives and it is the best I can get. The star in question was GSC 3827:466.

/Jake

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The Sloan Digital Sky Survey Photometric Catalog gives a Vmag for this star of 15.03. So, the Guide Star Catalog photometry appears to be pretty much spot on in this instance.

Bill in Flag

--------------------
Grand Canyon Adventure
Lowering the Threshold

18" Obsession
4.5" Meade 4500
10x50 Swift Audubon

Cosmic Voyage

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