Night vision at altitude

[AustinBoston]

In the summer of 2001, we spent some time near the Grand Canyon.  We stayed at a campground in Jacob Lake, AZ, which is on the Kaibab Plateau.  

While we were there, we took a day to visit Bryce Canyon National Park.[/quote].  It was a long day, and included viewing the canyon (more like a series of u-shaped washouts from a cliff), doing some horseback riding, and getting soaked in a thunderstorm.  Bryce is well worth seeing.  It was a long day, and we squeezed it for all it was worth.  It was past sunset when we headed back to the campground, and it was a bit of a drive.

PJay was driving, and we had just passed through a small town when I told her I was looking for a place to pull over to look at the stars.  The night was spectacularly clear, and there was no moon.  We both dedicated ourselves to watching the side of the road for wildlife.  After leaving a small town, we started up one of several passes we had to cross.  We went up, and up, and up.  

Near the top, there was a small parking area, and that is where we stopped.  The kids were asleep.  There was a small parking area just off the side of the road.  It may have been posted, but there wasn't going to be anybody coming by to complain.  We hadn't seen a car outside a town in about an hour.  Time has erased my memory as to just where we stopped.  I remember figuring the altitude was just under 9,000 feet at the time, but using Google Earth, I can't find a spot on our route that meets what I remember of it and is near 9,000 feet.

I was actually a bit disappointed with the starscape.  I expected to see more than at lower altitudes because so much of the Earth's atmosphere is below you at that altitude.  But it was not impressive.  I figured at the time that the light from the headlights had dulled our night vision.  We'd give it some time, and our eyes would adjust.  After 20 minutes, it was clear that night vision was not significantly improving.  We eventually moved on and headed home.  In the years that followed, I learned that night vision actually decreases with altitude.  The lack of oxygen (at 9,000 feet, you get 20% less oxygen with each breath than at sea level) dulls the sensitivity of the retina.  

Today, the FAA requires pilots flying unpressuraized aircraft at night above 5,000 feet to use oxygen.  It used to be 10,000 feet day or night, and is still 10,000 feet (only another 1,000 feet higher than we were) in the day.  There is a part of me that wishes I realized that at the time.  A few days later, we drove out of Death Valley late at night, arriving in Vegas after Midnight.  It was just as dark, just as clear, and just as moonless in Death Valley, but it was 9,000 feet lower in elevation.  The things we miss without realizing it.

Austin

[CajunCamper]

Austin, you know some S@%T. All along I thought it was my 46 year old eyes giving me problems.

CajunCamper

[naganthunter]

Austin, you know some S@%T. All along I thought it was my 46 year old eyes giving me problems.

CajunCamper

Hypoxia's the name, your senses are the game....sounds like you might be a pilot Austin?

Hypoxia can also effect your ablity to think straight.  If you're a smoker, you can become hypoxic at even lower altitudes...I guess we all ought to carry some supp O2 while camping at high altitudes!  God knows a pop-up ain't pressurized!!    :p

[JimS]

Not only do you have to let your night vision adjust, which can take about three hours, but coming from a relatively low elevation to 9000 feet will have an effect.  You have to get acclimated to the elevation which requires at least 24 hours per 1000 feet gain.  But from experience, this breaks down when you get above 6000 or so and acclimation takes more time.
I live at 6000 feet and work at 7000 and it took me months to get use to the elevation, but now after 30 years, I don't even notice it.
Also, I have noticed that when I get out with my telescope, even at higher elevations, heat shimmer can have a big effect on how much you can see.  I like cold, still nights with no star flicker, then the heavens just come alive!