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High Altitude Astronomy: Does it make that big of a difference?

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#1 2LiveAndDieInLA

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Posted 17 November 2015 - 07:40 PM

I know most of the world's great telescopes are located on mountain tops or inland in high altitude areas.  I understand this.

 

However, for the amateur astronomer or astrophotographer, how much of a difference does high altitudes make when dealing with reasonable apertures?  (ie, under 30 inches)

 

Has anyone here ever done astrophotos above 8,000 feet?  Was there a significant difference?

 

I can imagine being 10,000 feet up would make some difference.  That's two miles of dense atmosphere you are avoiding.  The air gets quite thin above that level.



#2 csrlice12

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Posted 17 November 2015 - 07:53 PM

If you're used to it, altitude can make for some of the most transparent skies you'll ever see...if you're not used to it, its hard to see when you can't breathe......


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#3 hbanich

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Posted 17 November 2015 - 08:00 PM

I can attest that the benefits of visual observing at 7 to 9 thousand feet are significant. As you already noted, you're above the thickest part of the atmosphere and that definitely shows in the eyepiece. Transparency and contrast are definitely boosted.

 

Plus there's enough air to breath - get much above 9000 feet and the lack of oxygen eliminates what you've gained from altitude. A camera won't care, but the operator might.


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#4 GJJim

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Posted 17 November 2015 - 08:24 PM

The big optical observatories in Chile (Tololo, Pachon, Paranal) offer an unusual combination, excellent seeing conditions and good transparency at relatively low altitudes. Average people can function at 8000-9000 feet without becoming muddle-headed. 

 

The same is true for amateurs, as long as we stay below ~9500 feet we can enjoy the advantages of the thinner air above without losing visual or mental acuity. Above that altitude our visual senses are dulled, and above 12K feet almost everyone will suffer slowed thought processes and less coordination. Some people might also experience altitude sickness if they visit a mountain site without first spending time and getting acclimated at an intermediate level.

 

Our club has observing sites at 6000, 8000, and 10700 feet MSL. All are quite dark (SQM 21.3-21.9), but there is a visible difference in the zenith sky "blackness" at these different locations. 


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#5 bobzeq25

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Posted 17 November 2015 - 08:37 PM

What makes a huge difference to an amateur astrophotographer are dark skies.  1 hour of data can easily be worth 10 in many people's backyards.  Discussed here, with examples:

 

http://www.samirkhar...-exposures.html

 

The high altitude is an extra advantage for the big scopes.  But the site needs to be chosen carefully, mountains are frequently subject to winds that seriously impact seeing. 

 

A mountain away from the jet stream and developed areas, in the middle of an ocean (Hawaii) or a desert (Chile) is the hot setup.  Dark skies are more available to most amateurs.


Edited by bobzeq25, 17 November 2015 - 08:40 PM.


#6 Scott99

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Posted 17 November 2015 - 08:50 PM

 

Our club has observing sites at 6000, 8000, and 10700 feet MSL. All are quite dark (SQM 21.3-21.9), but there is a visible difference in the zenith sky "blackness" at these different locations. 

 

wow, which club is it?  Maybe I should make that move to CO…..


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#7 GJJim

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Posted 17 November 2015 - 09:15 PM

 

 

Our club has observing sites at 6000, 8000, and 10700 feet MSL. All are quite dark (SQM 21.3-21.9), but there is a visible difference in the zenith sky "blackness" at these different locations. 

 

wow, which club is it?  Maybe I should make that move to CO…..

 

 

We're out in Grand Junction, the Western Colorado Astronomy Club, new members always welcome.  :grin: The 6000 ft. site is on the Colorado National Monument, about a 15 minute drive from downtown. It's a 45 minute drive to the other two sites on the Uncompahgre Plateau and the Grand Mesa, and they tend to be a bit snowy from Dec-Apr.


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#8 AndrewXnn

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Posted 17 November 2015 - 10:22 PM

I've viewed from Mt Lemmon near Tucson.

It's about 9,150' elevation.

However, when I was there the dew point was around 52F.

That's not much drier than my home which is further north at sea level.

 

In comparison, viewing was good, but not fantastic.

Being so close to Tucson, there was too much light pollution.

 

So, my take is that while elevation does play a role, it's not as important as dew point and light pollution.

Water vapor in the atmosphere is more of a detriment than oxygen & nitrogen.

At the same elevation skies are clearer during cold nights than warm.



#9 Feidb

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Posted 17 November 2015 - 10:31 PM

I've seen some of the best views at -192 feet. At 8K+ feet, I've been slammed by inversion layers and all kinds of other issues. Mountains and high altitude can be a trap for weather events just as much as basins. It depends on where the altitude is at. Logic would tell you that being above all the gunk is what you want, and it should be. However, WHERE that above the gunk is located is key. It's been quite a while since I've been to a high altitude place where the skies were great. I know they're around.


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#10 2LiveAndDieInLA

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Posted 19 November 2015 - 01:55 PM

It would be interesting to use one of these on a mountain to find out how great it really is.

 

http://unihedron.com/projects/darksky/



#11 Tony Flanders

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Posted 19 November 2015 - 02:24 PM

It would be interesting to use one of these on a mountain to find out how great it really is.

 

http://unihedron.com/projects/darksky/

Not useful for this purpose. At a site free of artificial light pollution, all the important light sources (airglow, zodiacal light, starlight) are well above the top of Mt. Everest. So all other things being equal, an SQM will actually measure a dark mountaintop as being brighter (nominally worse) than a dark sea-level site. That's because the atmosphere will absorb more of those natural light sources at sea level than on a mountaintop.

 

But since natural light sources are what you're trying to observe in the first place, that absorption is clearly a bad thing.

 

An SQM can measure skyglow, but it cannot measure transparency, which for amateurs is the main purpose of going to higher altitudes.


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#12 2LiveAndDieInLA

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Posted 19 November 2015 - 02:36 PM

 

It would be interesting to use one of these on a mountain to find out how great it really is.

 

http://unihedron.com/projects/darksky/

Not useful for this purpose. At a site free of artificial light pollution, all the important light sources (airglow, zodiacal light, starlight) are well above the top of Mt. Everest. So all other things being equal, an SQM will actually measure a dark mountaintop as being brighter (nominally worse) than a dark sea-level site. That's because the atmosphere will absorb more of those natural light sources at sea level than on a mountaintop.

 

But since natural light sources are what you're trying to observe in the first place, that absorption is clearly a bad thing.

 

An SQM can measure skyglow, but it cannot measure transparency, which for amateurs is the main purpose of going to higher altitudes.

 

 

Interesting.  Is there any device that can measure transparency?



#13 GJJim

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Posted 19 November 2015 - 03:51 PM

 

 

It would be interesting to use one of these on a mountain to find out how great it really is.

 

http://unihedron.com/projects/darksky/

Not useful for this purpose. At a site free of artificial light pollution, all the important light sources (airglow, zodiacal light, starlight) are well above the top of Mt. Everest. So all other things being equal, an SQM will actually measure a dark mountaintop as being brighter (nominally worse) than a dark sea-level site. That's because the atmosphere will absorb more of those natural light sources at sea level than on a mountaintop.

 

But since natural light sources are what you're trying to observe in the first place, that absorption is clearly a bad thing.

 

An SQM can measure skyglow, but it cannot measure transparency, which for amateurs is the main purpose of going to higher altitudes.

 

 

Interesting.  Is there any device that can measure transparency?

 

Not a device, but visibility of the magnitude 6.7-7 stars in the "cup" of the Little Dipper (Ursa Minor) is a simple way to judge transparency. These stars are at the threshhold of perception and I've found they are visible only with good transparency even at dark sites.



#14 2LiveAndDieInLA

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Posted 19 November 2015 - 04:52 PM

Not a device, but visibility of the magnitude 6.7-7 stars in the "cup" of the Little Dipper (Ursa Minor) is a simple way to judge transparency. These stars are at the threshhold of perception and I've found they are visible only with good transparency even at dark sites.

 

 


 

Interesting.  Is there any device that can measure transparency?

I guess part of the issue that presents is that which stars are and are not visible is dependent on the visual acuity of the observer.  Machines of some sort would be more consistent.


Edited by 2LiveAndDieInLA, 19 November 2015 - 04:52 PM.


#15 csrlice12

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Posted 19 November 2015 - 05:13 PM

distance from any and all light sources is best, not just the gas filter, but the fuel gage to let you know you've went far enough........



#16 Binojunky

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Posted 19 November 2015 - 05:30 PM

When observing from the summit of K2 I found my oxygen mask got in the way of the eyepiece and also the finder scope, TD.


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#17 Tony Flanders

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Posted 19 November 2015 - 05:46 PM

Interesting.  Is there any device that can measure transparency?

No. I've never even seen a good definition of transparency, much less a good way to measure it.
 
Professionals who engage in photometry (measuring the brightness of stars and other objects) do often measure extinction -- the fraction of the light from an object that doesn't reach your eye and/or instrument. But I'm not sure that's exactly the same thing as transparency, as the term is used by amateurs.

To measure extinction, you compare a star of known brightness at the zenith to a star of identical known brightness lower in the sky -- say 30 degrees above the horizon.

There's twice as much air between you and a star 30 degrees above the horizon as there is between you and a star at the zenith. So comparing the measured brightnesses of those two stars gives you the extinction.

This assumes that the air is equally clear or opaque all over the sky, which is not necessarily true. But photometry is only possible when that is reasonably close to true.

It's pretty easy to extract the apparent brightness of a star from a CCD image, but I'm not aware of any device that can do it in real time.

#18 2LiveAndDieInLA

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Posted 19 November 2015 - 06:08 PM

When observing from the summit of K2 I found my oxygen mask got in the way of the eyepiece and also the finder scope, TD.

jbarnet, World's Most Interesting Astronomer....is that you?   :lol:



#19 csrlice12

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Posted 19 November 2015 - 06:18 PM

Oh, well, if you gotta be picky about oxygen and all....... :lol:



#20 vsteblina

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Posted 19 November 2015 - 06:44 PM

The best night in my entire life was at 6400 feet on the Beaverhead National Forest.  The interesting part was that it did not seem that dark.  Until, I noticed what objects I could see naked eye.

 

However, my favorite observing sites are those that I can wear shorts while observing.



#21 precaud

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Posted 19 November 2015 - 06:54 PM

I walk out the door and observe from 7,000 ft. Transparency is generally better than seeing. Especially in the winter, when atmospheric moisture is at a minimum.

 

Is it better than lower altitudes? Dunno. I've never observed anywhere else.

 

But I must admit, reading some of the testimony of those who have done both makes me wonder what all you low-altitude folks are missing. Or not.



#22 GeneT

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Posted 19 November 2015 - 06:58 PM

Living in Ely, Nevada, altitude 6400 ft., I did not notice much difference going up to 9000 ft. If you go from 500 ft. to above 5000 ft., I believe you will notice how much cleaner sky objects look.


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#23 Starman1

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Posted 23 November 2015 - 03:58 PM

I know most of the world's great telescopes are located on mountain tops or inland in high altitude areas.  I understand this.

 

However, for the amateur astronomer or astrophotographer, how much of a difference does high altitudes make when dealing with reasonable apertures?  (ie, under 30 inches)

 

Has anyone here ever done astrophotos above 8,000 feet?  Was there a significant difference?

 

I can imagine being 10,000 feet up would make some difference.  That's two miles of dense atmosphere you are avoiding.  The air gets quite thin above that level.

I observed above 8300' from 1977 to 2012, and here is what I noticed about high altitude:

--the air is drier and clearer, on the average.  Less dew, and better transparency.

--the zenith isn't necessarily any darker, but faint features in galaxies and nebulae are easier.

--the sky from 45 degrees altitude down to the horizon, which constitutes the majority of the sky, is a lot darker and clearer than at lower altitude.  The Extinction Factor is much smaller. So the overall sky appears darker and clearer than a low altitude site with the same zenithal darkness.

--seeing is often better because the turbulence present in the lower atmosphere is reduced considerably.

 

However:

--above 8000', a lack of air can lead to altitude symptoms and even pulmonary edema in some extreme cases.  It's best to stay under 10,000' and most people

note an improvement in their eyesights down to below 8000', probably due to increased oxygen reaching the retina.

--older people suffer less from this than younger people.  The reason?  One doctor speculated that the older person has become used to a lower blood flow and oxygen level in the brain, so the lack of oxygen is less deleterious.  If that's true, it's sad.  I note, though, that 8000' caused me to occasionally have altitude symptoms when i was younger, but never does now.

--higher altitudes are usually much colder, so it takes a tolerance (and the right clothing) for cold, even in the summer.  I have seen a 32°F night in August at 8600' and even -40°F at 10,000' in October when the temperatures at 2000' were in the 80s and 60s respectively.  If you are like my wife, and think +60°F is cold, high altitude sites are not for you.

--since 99% of dark adaptation occurs on the retina, pupil diameter is relatively unimportant.  Keeping oxygen supplied to the retina is paramount.  The literature abounds with observers reports detailing how altitudes between 7000" and 8000" revealed fainter objects to the observers compared to altitudes over 9000'.

--high altitude is less of a problem for people who live their every-day lives at it.  If you live at 7000', a trip to 8000' will be inconsequential.  If you live at 300', though, a trip to 8000' can be much harder to accommodate physically.  It's much easier to acclimate to high altitude if you don't drink alcohol, drink a lot more water than usual, and confine any form of exercize to the 4th day at altitude or even later.

 

Unlike Vladimir, I have never observed at any site where shorts were the right attire at night since I left Indiana as a young man (there, you got eaten alive by bugs if you wore shorts at night).  It was in the high 40s at a desert site star party earlier this month.  Even at my low altitude (850') desert site, when it's 105°F in the daytime, it's 50°F at night.  If you can wear shorts at 50°, you're a better man than I am, Gunga Din.


Edited by Starman1, 23 November 2015 - 03:59 PM.

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#24 StarWolf57

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Posted 23 November 2015 - 04:54 PM

For astrophotos, yes it can make a difference, which explains why major observatories are generally found at high altitude. For visual - YMMV for the reasons others have stated.



#25 2LiveAndDieInLA

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Posted 24 November 2015 - 01:29 PM

Excellent post Starman1.  I appreciate the information.




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