Dave Nash sees to mag. 8.2 naked-eye at NSP
Brian Skiff
merits of sky quality and darkness of the Texas Star Party versus the Nebraska
Star Party, Dave Nash claimed to have seen some mag. 8 stars from NSP last
August. The test was "blind" in the sense that he made a sketch of a small
area of the sky without looking at an atlas to select stars. (As will be
seen, however, Dave is far from being blind.) The region is near the head of
Draco, the asterism sometimes called the "lozenge". Upon comparing with the
Tirion "Sky Atlas 2000", he was surprised to find that the most difficult
stars were marked with the smallest symbols on the chart, corresponding to
roughly mag. 8.
At my request, Dave supplied IDs for the specific stars involved. Only
the brightest star involved had any reliable published photometry, so I was
curious to find out just how bright these stars really were. I promised to
observe them photoelectrically at the first opportunity. I was able to do so
about 3 o'clock this morning, and the results are summarized below.
For the record, I used the Lowell 53cm photometric telescope, Stromgren
b and y filters, and a 29" diaphragm. I observed Dave's stars together with
nine primary and secondary Stromgren standards, whose colors extended beyond
the range of colors of Dave's stars. The y filter observations are
transformed to standard Johnson V magnitudes, as is usual in this sort of
work. (The Stromgren y filter has the same central wavelength as a V filter,
but is only ~200A wide, instead of ~1000A wide. For what it's worth, my
several hundred observations of Landolt equatorial standards show that I match
his V system systematically to within a couple thousandsth of a magnitude over
the color range -0.28 < B-V < 1.75. As a further historical aside, the
original primary standards for the UBV system were measured on the same 53cm
telescope in the mid-1950s by Harold Johnson and Daniel Harris.) The rms
errors of the linear fits to V magnitude and b-y color were +/-0.009 and
0.008, respectively. I would have preferred to use more standards, but these
nine were entirely adequate for the purpose at hand.
During the course of a general survey of mag. 6-8 stars, I had previously
measured the two brighter stars three and two times, respectively. This
morning's results agree with those observations well within their mutual
errors, so I am confident that the single observations of the fainter stars
are reliable to within about 0.015 mag. or better.
Name RA (2000) Dec V b-y spec SAO HD BD
HD160520* 17 37 14 +55 44.5 7.027 0.710 K0 7.2(GC) 7.18 7.4
.006 .003
HD162131 17 46 30 +53 34.7 7.609 0.088 A2 7.5(AGK1) 7.34 7.5
.005 .001
HD163010 17 50 31 +57 26.6 8.01 0.01 B9 7.5(AGK1) 7.9 7.7
HD161353 17 42 13 +52 03.4 8.06 0.58 K0 7.8(AGK1) 8.1 7.9
HD161179 17 41 23 +51 28.3 8.15 0.77 K2 8.0(AGK1) 8.1 7.9
* for HD 160520, Kornilov et al. (1991) give: V = 7.050, B-V = 1.158, from
four observations.
The table lists the stars along with 0'.1-precision positions. The new
magnitudes and colors come next. For the two multiply-observed stars, I give
the rms scatter of the data on the second line of each entry. For the fainter
three stars, I give the results to just two decimals. The spectral types are
listed directly from the HD catalogue, which is the only source of types for
these particular stars. My b-y colors combined with the spectral types show
that the sample consists of two early-A type stars (probably dwarfs) and three
garden-variety K-giants.
The final three columns are "visual" magnitudes from three sources: the
SAO star catalogue, the HD catalogue, and the BD. The original source for the
SAO magnitudes is given in each case. As you can see, the magnitudes in the
early catalogues aren't _so_ bad, but nevertheless usually report the stars
to be brighter than they really are, and scatter around "truth" by up to half
a magnitude.
In summary, Dave saw three mag. 8 stars from Merritt Reservoir, which
shows not only that NSP has a great site, but that Dave is a skilled visual
observer and also probably has acute (sharp) vision. He probably can see
similarly faint from similarly-good sites, such as TSP, or other high and dry
dark places. I've been observing from "perfect" sites in the desert Southwest
US and Chile for twenty years and haven't been able to go fainter than about
V=7.2, so my hat's off to ya, pal!
\Brian Skiff (b...@lowell.edu)
Louis Binder,O.D.
Does this mean the limiting magnitude challenge has been laid down for
TSP, WE the Fort Bend Bendonites shall see...TSP-37days and counting.
Results will be posted on our home page ;
http://rampages.onramp.net/~binder/
Louis S. Binder,O.D.
FBAC/HAS
John Ongtooguk
: ... In summary, Dave saw three mag. 8 stars from Merritt Reservoir, which
: shows not only that NSP has a great site, but that Dave is a skilled visual
: observer and also probably has acute (sharp) vision. He probably can see
: similarly faint from similarly-good sites, such as TSP, or other high and dry
: dark places. I've been observing from "perfect" sites in the desert Southwest
: US and Chile for twenty years and haven't been able to go fainter than about
: V=7.2, so my hat's off to ya, pal!
With no intent of detracting from anyone's abilities....I've
read that one can gain about 2 magnitudes over the usually
stated visual limit of around 6.5 by observing thru a short
tube, mask with a hole, etc., anything that will block most
of the sky. I think it was in Sidgewick's (speling ?) handbook.
Would such a technique be a better measure of sky conditions,
as it would minimize the impact of bright horizons ? Maybe
some zero power/aberration free binoculars are in order, made
from a couple of optical grade toilet paper tubes.
John Ongtooguk (jo...@vcd.hp.com)
Mark Gingrich
have pigged out on bilberry muffins and washed them down with mass
quantities of carrot juice! ;)
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Mark Gingrich gri...@rahul.net San Leandro, California
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dave Nash
>Dave Nash can see 8.2-magnitude stars? Holy smoke! Somebody must
>have pigged out on bilberry muffins and washed them down with mass
>quantities of carrot juice! ;)
OK, that's it. At first I thought it was due to being in a region
with very different soil characteristics. That turned out not to be
the case. I now know why the water at NSP tasted so different from
water out of urban supplies.
:-)
>--
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Mark Gingrich gri...@rahul.net San Leandro, California
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
Dave Nash, School of Chemical Sciences, University of Illinois
E-mail: na...@aries.scs.uiuc.edu; WWW: http://www.scs.uiuc.edu/~nash/
"Holy Smoke! Somebody blew up the Pope!"
Kenneth Drake
> With no intent of detracting from anyone's abilities....I've
> read that one can gain about 2 magnitudes over the usually
> stated visual limit of around 6.5 by observing thru a short
> tube, mask with a hole, etc., anything that will block most
> of the sky. I think it was in Sidgewick's (speling ?) handbook.
> Would such a technique be a better measure of sky conditions,
> as it would minimize the impact of bright horizons ? Maybe
> some zero power/aberration free binoculars are in order, made
> from a couple of optical grade toilet paper tubes.
>
> John Ongtooguk (jo...@vcd.hp.com)
I have a pair of these!! They're called 0-MAGS. 1x90 binos presented
to my x-wife as a gag gift. She got the Sony! I never thought of really
trying to use them. Thanks John for the idea. I'll post the results of
my
experiment.
Kenneth Drake
Kenneth Drake
writes:
Is Barbara Wilson still a "Bendonite"? If so, the challenge is no
contest!
"DRAKO"
Mel Bartels
positive effect at all (even using a separate tube for each eye).
You can get to 8.5 if you can manage to employ magnification without any
increase in the eye's aperture. This dims the sky background such that
the contrast between the star and sky increases to the point where the
star becomes visible. Now, if you could somehow make a mask and aim it
precisely to an arcminute or so in line with each eye, then you might be
able to see some gain.
--
Regards, Mel Bartels, programmer/technical analyst;
mailto:mbar...@efn.org
homepage http://www.efn.org/~mbartels/
How To Computerize a Dobsonian Telescope:
http://zebu.uoregon.edu/~mbartels/altaz/altaz.html
David W. Knisely
bilberrys or carrots). However, the most impressive thing I experienced was the
shadow that my hand cast on my nametag, caused by the Milky Way ("You know its
bright (dark) when the Milky Way casts shadows.") If you want to see the site for
yourself, come to the Nebraska Star Party, August 10-17, at Merritt Reservoir near
Valentine Nebraska. For more information, check out its web site at
http://www.4w.com/nsp , or E-mail to n...@infoanalytic.com for registration
information.
David Knisely
Dave Nash
> With no intent of detracting from anyone's abilities....I've
> read that one can gain about 2 magnitudes over the usually
> stated visual limit of around 6.5 by observing thru a short
> tube, mask with a hole, etc., anything that will block most
> of the sky. I think it was in Sidgewick's (speling ?) handbook.
Something similar is mentioned in Fred Schaaf's _The Starry Room_, in
which he refers to some limiting magnitude tests done using a shielded
sight tube (similar to what you describe). I don't recall what the
limit was, but it was (a) dimmer than +8.0 and (b) taken from the Lick
Observatory area in the early 20th century (i.e., before light
pollution was much of a problem).
I *have* taken some limiting magnitude measurements while wearing a
black cloth hood to screen out ambient skyglow, but I don't have
enough data on this to be conclusive. I was wearing the hood not to
hike dark sensitivity _per se_, but rather to help block a few
offending lights at the various sites I used. I think this added a few
tenths to typical limits from sites in eastern Illinois, but I haven't
tried from a genuinely dark site like NSP. (Hmmm..first time for
everything, right? :-)
> Would such a technique be a better measure of sky conditions,
> as it would minimize the impact of bright horizons ? Maybe
> some zero power/aberration free binoculars are in order, made
> from a couple of optical grade toilet paper tubes.
>
> John Ongtooguk (jo...@vcd.hp.com)
Kenneth Drake
writes:
At TSP not long ago (I think '94) Brian Skiff led me one fainter star
at a time at the zenith to mag 7.9. naked-eye. I was completely
blown-away because I never had tried it and didn't believe the stories
I had heard before. Trust me, it can be done.
Kenneth Drake
Klaas van Ditzhuyzen
I did from Australia, seeing Sirius at 3 pm local time after I looked it up
with setting circles with a 70mm telescope. I saw it along the telescope
with the naked eye.
Any other observations ?
Klaas
David W. Knisely
Since the last NSP, I have gotten to 7.0 from my local site several times (and
occasionally fainter). Before I went to the NSP, I was initally a little skeptical
about how faint I could go, but after a couple of quick checks, I was very happy,
and went back to my telescope (Dave was down the hill a bit from me, and he
continued to count the stars while I went bananas looking at things in the Milky Way
I had never seen before). Maybe we need some people to start a "how faint can you
go" research program?
David Knisely, Prairie Astronomy Club, Inc.
Stephen C. Wingreen
On clear, northern Florida winter nights, from our not-too-dark site in Lloyd, FL, I can
frequently count eight Pleiads. I'm not sure what the magnitude of the eighth Pleiad is,
but isn't it a little fainter than mag. 7? I wonder what I would see from a really dark site.
Steve
Grieg A. Olson
<kl...@uniface.nl> wrote:
> Does somebody have experience with seeing stars in the daytime ?
>
> I did from Australia, seeing Sirius at 3 pm local time after I looked it up
> with setting circles with a 70mm telescope. I saw it along the telescope
> with the naked eye.
>
I also saw Sirius in the late afternoon when the sun was still up and
Sirius was in the south.
Grieg
The following disclaimer was written by a company lawyer. I take no responsibility for it.
Standard Disclaimer______________________
Opinions expressed herein are my own and may not represent those of 3M.
Dave Nash
>On clear, northern Florida winter nights, from our not-too-dark site in Lloyd, FL, I can
>frequently count eight Pleiads. I'm not sure what the magnitude of the eighth Pleiad is,
>but isn't it a little fainter than mag. 7? I wonder what I would see from a really dark site.
Nope. I've been able to see as many as 9 without much trouble, but
under less than optimal conditions (ones that don't permit seeing
magnitude +6.5 stars, never mind +7.0 or dimmer) The 6 Pleiads that
most people see without trouble are 3rd or 4th magnitude; there are
several other 5th magnitude stars in the bunch. I forget the exact
numbers, but I believe there are around a dozen other stars brighter
than magnitude +7.0 in the Pleiades (excluding the 6 brightest ones).
My limiting magnitude based on Pleiades counts is *always* much worse
(at least 1 magnitude) than that based on the "sketch part of the sky"
approach that Brian Skiff and I have mentioned on s.a.a.
recently. Part of the problem is that the Pleiades are so close to
each other that with averted vision, the stars tend to merge together,
making it hard to identify (let alone confirm) stars close to the
limit.
Your best bet for figuring out Pleiades limits (absent more photometry
from Mr. Skiff :-) would be to get a good star catalog and look things
up (apparently the YBSC, which is complete down to ~+6.5, has pretty
reliable magnitudes nowadays), or else get something like _Sky Atlas
2000_ and count the different sized dots.
>Steve
Mel Bartels
at least 20 Pleiades, it is a bad sky for me. I'll have to see to what
magnitude penetration that goes, but I would guess 6.5 to 7.
--
Regards, Mel Bartels
mailto:mbar...@efn.org homepage: http://www.efn.org/~mbartels
how to computerize a dobsonian telescope:
http://zebu.uoregon.edu/~mbartels/altaz/altaz.html
Dave Nash
>I use the counting of Pleiades to estimate sky clarity. If I don't see
>at least 20 Pleiades, it is a bad sky for me. I'll have to see to what
>magnitude penetration that goes, but I would guess 6.5 to 7.
For the record, I checked the magnitudes of the Pleiades stars using the
starchart program Voyager II. VII uses the SAO catalog, which, unfortunately,
is outdated in its magnitude estimates. Nevertheless, this should be a useful
starting point. I don't know where the exact boundary of the Pleiades is, so
as a crude heuristic I assumed that all stars within 1 degree of Alcyone (the
brightest member) belonged to the cluster.
Stars with magnitudes of:
2.5 - 3.5: 1
3.5 - 4.5: 5
4.5 - 5.5: 3
5.5 - 6.5: 4
6.5 - 7.5: 12
7.5 - 8.0: 4
Voyager's implementation of the SAO catalog stops at magnitude 8.0 on
my version, so I don't have the full total of 8th magnitude stars.
Note also that the six "easy" stars -- the ones most people see
readily -- are all 4.5 or brighter, and if you can get down to only
5.5, the number of Pleiades should go up to 9 -- assuming your vision
is sharp enough to resolve all the suckers.
>--
>Regards, Mel Bartels
>mailto:mbar...@efn.org homepage: http://www.efn.org/~mbartels
>how to computerize a dobsonian telescope:
>http://zebu.uoregon.edu/~mbartels/altaz/altaz.html
Kenneth Drake
A. Olson) writes:
>
>In article <4kd3af$4...@news.knoware.nl>, Klaas van Ditzhuyzen
><kl...@uniface.nl> wrote:
>
>> Does somebody have experience with seeing stars in the daytime ?
>>
>> I did from Australia, seeing Sirius at 3 pm local time after I
looked it up
>> with setting circles with a 70mm telescope. I saw it along the
telescope
>> with the naked eye.
>>
>
>I also saw Sirius in the late afternoon when the sun was still up and
>Sirius was in the south.
>
>Grieg
I've seen Sirius twice in daylight.
Once from TSP around 2:00 P.M. through a fellow amateurs scope.
Next time was from Lake Conroe in mid November of '88 or '89.
I was wrapping up an attempt to see the Leonid meteor shower as
daylight arrived. We had the 10" f/5.6 tracking Sirius and were
constantly pulling away from the scope to see it naked eye when we
realized the sun had come up. We were not able to hold it for more
than 5 seconds or so at a time.
Kenneth Drake
Paul Schlyter
I saw Aldebaran once i daylight, while observing a daylight occultation
of Aldebaran by the moon. Then it was of course easy to find Aldebaran
in the telescope: point the telescope at the moon and look a little beside
the moon. The instrument was a small 2.4" refractor -- this was some 15
years ago.
--
----------------------------------------------------------------
Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF)
Grev Turegatan 40, S-114 38 Stockholm, SWEDEN
e-mail: pau...@saaf.se p...@home.ausys.se