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.
--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.