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General Astronomy >> Light Pollution

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mountain monk
Carpal Tunnel
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Reged: 11/06/09

Loc: Grand Teton National Park
Re: Bortle scale accuracy? new [Re: JayinUT]
      #5981900 - 07/20/13 07:43 PM

Gentlemen: You all know far more about astronomy than I will ever know. I will only comment on "small societies..."

Because we live where we do, we have a somewhat limited idea of life at high altitude. A few factoids about places I have been, or been near to.

La Rinconada, Peru is a city of 30,000+ inhabitants at 16700 feet. Cerro de Pasco, Peru is a city of over 70,000 inhabitants at 14200 feet. Rongbuk Monastery, on the way to base camp for the north side of Everest, lies at 16340 feet. When I visited, it was still mostly ruins (destroyed by the Cultural Revolution), but was being rebuilt and is now occupied and can be reached by road. When the first British Everest expedition reached Rongbuk, in 1922, it housed 450 monks. In his book Himalayan Pilgrimage, David Snellgrove (London School of Oriental and African Studies and perhaps the preeminent authority on Tibetan culture of his generation) describes his travels to Dolpo, part of Nepal but Tibetan in culture. He describes villages at 16500 feet and says that several are higher. Petter Matthiessen describes them in his book The Snow Leopard, which won the National Book Award. I have spent time with Peruvian Indians and Tibetans and Sherpas at these altitudes and I have found no reason to believe their vision is inferior to our own. Going high with acclimatization, or living high, does not negatively affect vision. The body adapts. But that's only one half of the argument.

The other half is the argument that you can see more. Yes, of course, the law of diminishing returns sets in above...what? I cannot prove that you can see more, obviously. I will note that the Kun Lun Range is just south of the Taklamakan (various spellings) Desert, one of the driest places on the planet and very cold--well below zero in the winter. (And remote from light sources.) There, and in the Karakoram, you use camels, not yaks. I wish we had observations from there, but to my knowledge, we don't. I'll bet my cookies on a Tibetan kid born at 18000 feet and given a bit of training at observing... I wish I could do just that.

I concur with everything that Jay says.

Dark skies.

Jack

Edited by mountain monk (07/20/13 08:46 PM)


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BrooksObs
professor emeritus


Reged: 12/08/12

Re: Bortle scale accuracy? new [Re: Tony Flanders]
      #5982044 - 07/20/13 09:18 PM

Quote:

You are mis-remembering. Only 25% of the atmosphere is below you at 10,000 feet. The 50% mark is reached at 18,000 feet -- coincidentally around the limit of long-term human survival. - Tony




From 3 separate citations I consulted: "6000-10,000 feet is the altitude range some people may start to experience problems related to altitude. AMS, or Acute Mountain Sickness symptoms may set in at any altitude above 6,000 feet. At 10,000 feet, the atmosphere is only 50% of that found at sea level."

BrooksObs

Edited by BrooksObs (07/20/13 09:19 PM)


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mountain monk
Carpal Tunnel
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Reged: 11/06/09

Loc: Grand Teton National Park
Re: Bortle scale accuracy? new [Re: BrooksObs]
      #5982074 - 07/20/13 09:43 PM

Yes, but the key words here are "some" and "may."

Our company (I worked for them for over thirty years and was president) takes people up the Grand Teton. The typical client flies in from sea level or near sea level to 6000-7000 feet, spends two days in climbing school at 7000 feet, goes up to our hut at 11700 feet on the third day and climbs the Grand Teton--13700 feet-on the fourth day and returns to 6000-7000. Our rate of difficulties with AMS, after eighty years in business, is a small fraction of one percent. This is not to deny the possibility of AMS or its seriousness. I've had both forms--pulmonary and cerebral. It's serious but rare at the elevations you mention and not, I think, something that should concern most astronomers.

Dark skies.

Jack


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Ekyprotic
super member
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Reged: 11/28/12

Re: Bortle scale accuracy? new [Re: BrooksObs]
      #5982184 - 07/20/13 11:12 PM

Thanks Brooks, Tony and everyone else! Lots of great info here :-) I'm going to set the planetarium to Mag 7.5 based on this. This answers my other question about elevation- would some place even higher than what the Andes can provide (like, near Mt Everest), be even better? (There's a Mt Everest panorama in SNPP.) I take it the answer is no, but not for the reason I thought..... I figured the light pollution from India to the south would be a problem. The Andes are in an ideal location, being close to the Pacific Ocean.

A related question to this I had was what is the FOV of the human eye? Based on what I've read it's close to 180 x 180 degrees, but I also read that to visually view stars that are dimmer than Mag 6, you need to concentrate on a much smaller FOV (I surmise this was along the lines of what Brooks was saying regarding what's necessary to see very dim stars.) It was recommended to make the starting FOV in the program 120 degrees.... which is where I have it. In any case, the program suffers from distortions if the FOV is greater than 167 degrees.

Sources:

http://clarkvision.com/imagedetail/eye-resolution.html

http://www.astronomyforum.net/astronomy-beginners-forum/116992-human-eye-fov....

http://www.astronomyforum.net/amateur-astronomy-forum/38747-h-alpha-detection...

160 x 175

http://en.wikipedia.org/wiki/Naked_eye

http://en.wikipedia.org/wiki/Human_eye#Field_of_view

I found the discussion about Peru particularly interesting because I was wondering if ancient cave art depicted astronomical objects that we can only see with telescopes now. I remember reading that Sirius B may be such an object.

I also read that the Nazca Lines may have been inspired by constellations (maybe Orion) and perhaps even the dark lanes in the Milky Way.

https://en.wikipedia.org/wiki/Nazca_Lines#Purpose

my favorites are condor, giant, spider, dog and the monkey

https://en.wikipedia.org/wiki/Sirius_B#Etymology_and_cultural_significance

Dogon[edit]
See also: Nommo
The Dogon people are an ethnic group in Mali, West Africa, reported to have traditional astronomical knowledge about Sirius that would normally be considered impossible without the use of telescopes. According to Marcel Griaule's books Conversations with Ogotemmęli and The Pale Fox they knew about the fifty-year orbital period of Sirius and its companion prior to western astronomers. They also refer to a third star accompanying Sirius A and B. Robert Temple's 1976 book The Sirius Mystery, credits them with knowledge of the four Galilean moons of Jupiter and the rings of Saturn. This has been the subject of controversy and speculation. According to a 1978 Skeptical Inquirer article it is possibly the result of cultural contamination.[115] Some have suggested the contaminators to have been the ethnographers themselves.[116][117] Others see this explanation as being too simplistic.[118]



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JayinUT
I'm not Sleepy
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Reged: 09/19/08

Loc: Utah
Re: Bortle scale accuracy? new [Re: BrooksObs]
      #5982265 - 07/21/13 12:45 AM

I'll share a couple of links on altitude and people can read and do what they want with the info. I think we need to get back to discussing dark sites.

Wm Keck Observatory Link.

Institute for High Altitude Medicine Link

BaseCampMD.com

The site above lists this: High Altitude is 5000 to 11500 feet; Very High Altitude as 11500 to 18000 feet; Extreme Altitude above 18000 feet.

UIAA website


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Tony Flanders
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Bortle scale accuracy? new [Re: BrooksObs]
      #5982457 - 07/21/13 06:09 AM

Quote:

From 3 separate citations I consulted: "6000-10,000 feet is the altitude range some people may start to experience problems related to altitude. AMS, or Acute Mountain Sickness symptoms may set in at any altitude above 6,000 feet. At 10,000 feet, the atmosphere is only 50% of that found at sea level."




Gotta check your sources! That's especially true on the internet, where incorrect information propagates like wildfire. The first two statements are correct, the third is not.


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Ekyprotic
super member
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Reged: 11/28/12

Re: Bortle scale accuracy? new [Re: Tony Flanders]
      #5984097 - 07/22/13 07:46 AM

This is more of an academic question but does anyone have any idea what the limiting magnitude may be from outer space? Assuming that neither the sun nor the moon is visible from this position in space.

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Ekyprotic
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Reged: 11/28/12

Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6000965 - 08/01/13 03:25 AM

Are there or have there been any reported naked eye sightings of the planet Neptune? I figured this would be a good target for those in areas of very little artificial light pollution as it is close to Mag 8 (7.78-8.00).

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Ekyprotic
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Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6000993 - 08/01/13 04:34 AM

Found this post from 1999 about a guy who can see down to Mag 8.5

http://tech.groups.yahoo.com/group/amastro/message/898


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JayinUT
I'm not Sleepy
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Reged: 09/19/08

Loc: Utah
Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6001341 - 08/01/13 11:40 AM

One thing I have found in the hobby is that for 1 person that is vocal on their abilities, there are usually 2 or 3 that are not. So is viewing from 8.0 to 8.5 as rare as we might thing for the serious visual observer? Isn't it just possible that someone can do it and just isn't vocal about it, doesn't feel the need to share or just doesn't want to prove that they can do it. They know they can do it, they've done it and so for them that is enough? How many of these people are there in the hobby I wonder?

Edit: I don't mean to imply that being vocal or sharing is bad, or bragging. I think many people just share what they find and what they are capable of. However, I am suspicious that there are more people who can and do wonderful things and just don't publish them for whatever reason. Much like I know of several people that have done 12 or more of the AL programs but never put in for the reward. They know what they can do. Their close group of observing friends know what they can do and that is all that matters to them. So I think there are more out there than we may think who can push the limits.

Edited by JayinUT (08/01/13 11:44 AM)


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Tony Flanders
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Re: Bortle scale accuracy? new [Re: JayinUT]
      #6001410 - 08/01/13 02:21 PM

Quote:

So is viewing from 8.0 to 8.5 as rare as we might thing for the serious visual observer?




Yes. Amateur astronomy is a small world; if there were lots of people who could do this, I would know about it.

Quote:

I think many people just share what they find and what they are capable of. However, I am suspicious that there are more people who can and do wonderful things and just don't publish them for whatever reason. Much like I know of several people that have done 12 or more of the AL programs but never put in for the reward. They know what they can do. Their close group of observing friends know what they can do and that is all that matters to them.




Sure, but among that close group of friends would be somebody I know, or somebody who knows somebody I know.


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Ekyprotic
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Reged: 11/28/12

Re: Bortle scale accuracy? new [Re: Tony Flanders]
      #6002210 - 08/01/13 10:01 PM

Tony, I thought it was interesting how the person who wrote that piece said that his co-observer could see half a magnitude to a full magnitude lower than he could, at the same site, at the same time. So maybe there are some significant variances between people.

I've been scouring the net looking for any reports of naked eye observing of Neptune and have yet to find any. I have a thought......

Isn't it true that the human eye is particularly sensitive to red light? So is it possible that those very dim stars that some people can see are red stars? Maybe the reason why there are no reports of naked eye seeing of Neptune is because it's blue-green and the human eye isn't as sensitive to that color light as it is to red? Just an idea.....


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JayinUT
I'm not Sleepy
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Reged: 09/19/08

Loc: Utah
Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6002476 - 08/02/13 01:33 AM

There's a lot out there on the limits of naked eye DSO's.

First is Brian Skiff's list of objects that have been seen at this link.

There is this threat over at Astronomy where a poster states that he can see M101 and M51 naked eye and the rebuttals to that claim. Link 2 I find that thread an interesting read.

In this report at this link, it is reported that Brian Skiff has seen M81 as "a threshold object."

Brian Skiff reports that from a true dark site the limit (for observing naked eye) from dark sites seems to depend strongly on visual acuity. I'll provide that link at the bottom on his comments on altitude.

In terms of Neptune, Brian Skiff at this link failed to find it in 2005, though he believes it should be "straightforward with patience from Chile or elsewhere in the south."

My take from this and from someone who regular observers at sites form 21.64 to 21.77 is that it takes a dark site like this and observing there from a regular basis to really begin to train the eye to see to its limits. That limit will vary depending on the person. I think you can gain experience from observing as often as you can, and for a long time, the more you do it the better trained the eye is. It helps when you start going to a dark site. However, regular and consistent training of the eye at a dark site, which Brian Skiff states is 21.5 arch seconds or better, enhances the training. I'd be most interested in hearing from Tony how observing in light pollution in his opinion also helps in visual observing.

In terms of observing at altitude I share what I found there from Brian. He states:

"However, for visual observing, if you go too high, you'll lose visual sensitivity simply because not enough oxygen is getting to your brain. The optimum altitude range seems to be from about 1500 up to perhaps 3000 meters (5000 to 9000 feet). Below 1500m, the amount of crud increases dramatically, and above 3000m most people have at least mild effects from lack of oxygen. Visual observing from Mauna Kea without bottled oxygen is pretty crummy. Remember that astro-observing is mostly at the threshold of acuity, so even small physiological effects from altitude (or ill health etc) will have pronounced effects on your vision in these circumstances. (When you're observing sometime at high power, try exhaling and not taking a breath for a good chunk of a minute: before you get dizzy, the eyepiece view will fade out and go grainy.) For what it's worth, acclimation to altitude appears to be independent of age, gender, or physical condition---but the genetic engineering necessary for high altitude living has already been worked out: they're called Bolivians!"

That quote and the one above is at this link. His findings go with what I find, though I don't find an impact on myself until I go well over 10,000 feet. That is why my FOR me, my maximum height is between 9000ft and 10000ft. I often observe between 6000 and 7000 feet.

Anyway, just sharing what I found in spending some time looking around and I look forward to others insights.

Edited by JayinUT (08/02/13 01:35 AM)


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Ekyprotic
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Re: Bortle scale accuracy? new [Re: JayinUT]
      #6002562 - 08/02/13 03:48 AM

Thanks! This is exactly the kind of research I find most interesting! What's the highest level of seeing that any site that you know of has attained? 22? Also, I find it quite interesting that it seems like a number of people have reported being able to see to Mag 8.5 but no one any higher than that, not even 8.6 or 8.8? Did you find any reports for anyone claiming to have gone beyond 8.5?

Another question I have is how does myopia affect the dimmest objects we can detect? My vision is 20/60 (20/35 in my right eye and 20/80 in my left eye)...... would this affect the minimum magnitude I can see by a significant amount? Unaided or with glasses? The funny thing is when I shut my left eye and just look through my right eye it actually feels like I am wearing glasses because my vision seems so much sharper.


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Ekyprotic
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Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6002570 - 08/02/13 03:57 AM

haha that was an interesting thread- that guy was talking about how someone having a porch light on 5 miles away drives him nuts and he doesn't have any sources of artificial light pollution within 10 miles of his house.

further down in the thread he said this:

One night here I went to ~900X with my 12.5" on Saturn and saw near photographic detail. I consider seeing like that night a once in a lifetime thing, but I still have my notes and remember it vividly.

and someone responded that he'd read that 9th mag stars had actually been seen visually from Mauna Kea?

Dave - I don't want to hyjack the thread but in Stephen O'Meara's book "The messier Objects" he mentions that he was able to see stars of 8.2 with the unaided eye while doing his research in HI on Mauna Kea (at 9,000'). He mentions that others with him have made similar (8th-9th) sightings in the world's best observing sites. So I'm assuming that for extended objects in the same seeing conditions, could it be possible to include M101, even with its very low surface brightness, as a naked eye object under the best of conditions? Mr Q



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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Bortle scale accuracy? new [Re: Tony Flanders]
      #6002590 - 08/02/13 04:24 AM

Quote:

Yes. Amateur astronomy is a small world; if there were lots of people who could do this, I would know about it.

[...]

Sure, but among that close group of friends would be somebody I know, or somebody who knows somebody I know.




So astronomy's version of "Six Degrees of Kevin Bacon" is "Two Degrees of Tony Flanders".


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Ekyprotic
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Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6002595 - 08/02/13 04:35 AM

This thread here indicates SQM readings of 22.1 or so consistent in the outback of western australia and namibia- higher readings also possible, but only under overcast skies. What does 22.1 translate to in terms of limiting magnitude?

http://www.iceinspace.com.au/forum/archive/index.php/t-71823.html


from that site

I note the highest reading from Australia is 22.07 from outside Mullawa in WA, which is about 100km West of Geraldton and 500km North of Perth. I have no doubt it's right. There are 3 men and a dog per 1,000 square km out there. But not close to the equal of several readings in CONUS? I note the highest reading from New Zealand is 22.02 from Benmore Peak Observatory. Again I have no doubt it's correct as indicated in one of my earlier posts.

and

12-03-2011, 12:20 AM
Hi all,

It was me who submitted the SQM-L 22.07 reading from outside Mullewa, W.A. I visited a remote farm together with Finnish amateur astronomers in December 2009 to do some really dark DeepSky-observations. They had also a SQM which showed 22.09 as best. In a series of three readings I got 22.01, 22.02 and 22.07. That was when I pointed to a relatively "blank" region of the sky, not the Milky Way or the zodiacal light. From here we observed the Light bridge between LMC and the Milky way. See my thread

http://www.iceinspace.com.au/forum/showthread.php?t=68088

From my regular observing site here in Sweden, the SQM-L has shown 21.48 at most and my naked eye limiting magnitude was 7.4. My Australian site is way darker than that!

/Timo Karhula

This is from the second link- much more on the site!

I'm an amateur astronomer from Sweden who regularly makes a trip to Western Australia, because I have an apartment in Geraldton after my late father. Last year, in November - December, I made a trip 130 kms to the inland where light pollution is unknown. My naked eye limiting magnitude was 7.9 and the SQM-L meters showed 22.09 magnitude per square arc-seconds! For the first time in 13 trips south of the equator, I observed a bridge of light between the LMC and our Milky Way. I have written a lengthy article of my astro-trip for the Deep-Sky Observer magazine of the Webb Society which will be published this winter or next spring. Here is an excerpt from my article:

"The light bridge of the Large Magellanic Cloud

The journey’s most exciting and unexpected sky phenomenon that we observed, was without a doubt, the light or materia bridge (as I call it) of the Large Magellanic Cloud, LMC. It is not even scientifically studied yet and only a handful of people have reported it in the literature!

......

I suspect a sky capable of showing stars to magnitude 7.5 or has a darkness of about SQM 21.9 is necessary to show the light bridge between the LMC and the Norma Starcloud. Has anyone on this forum seen the bridge of light? It would be very strange if nothing more is known of this naked-eye feature!

Clear Skies!

Timo Karhula


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Ekyprotic
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Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6002597 - 08/02/13 04:44 AM

hmmm this cant be right, this site indicates that a limiting mag of 8.5 equates to an SQM reading of 28?!

http://www.cruxis.com/scope/limitingmagnitude.htm

If you enter a specific SQM reading it calculates the limiting magnitude automatically


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Tony Flanders
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Reged: 05/18/06

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Re: Bortle scale accuracy? new [Re: derangedhermit]
      #6002639 - 08/02/13 06:26 AM

Quote:

So astronomy's version of "Six Degrees of Kevin Bacon" is "Two Degrees of Tony Flanders".




Make that "two degrees of Sky & Telescope." But the same could be said of many of the people who post here, who are equally embedded in the amateur-astronomy community. It really is a very small world.


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Tony Flanders
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Bortle scale accuracy? new [Re: Ekyprotic]
      #6002642 - 08/02/13 06:29 AM

Quote:

This thread here indicates SQM readings of 22.1 or so consistent in the outback of western australia and namibia- higher readings also possible, but only under overcast skies. What does 22.1 translate to in terms of limiting magnitude?




It doesn't. The correlation between SQM readings and limiting magnitude is extremely tenuous. In my opinion, essentially non-existent for SQM readings darker than 21.6 or thereabouts.


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