A Darker View

In some of the forums I participate, there have regularly been discussions into the effects of high altitude on eyesight. When observing visually with a telescope eyesight is often pressed to the limits, and any loss of vision due to high altitude and low oxygen should impact visual acuity. As someone who regularly spends time at high altitude I have always wondered just how much is lost?

The effects of working at 13,600ft are significant, strenuous effort readily leaves one out of breath, minor headaches are not uncommon, and often you are just tired at the end of the day. But I have never noted significant loss of cognitive or visual ability.

I have had a couple opportunities to try oxygen at the summit in the past, but never with a telescope available. This last week I tried just that. Viewing several objects without oxygen and the with, in an effort to observe just how much different a little oxygen actually has on the ability to see dim objects in the eyepiece.

The unit we use at Keck is a HELiOS personal oxygen system. This uses a small reservoir of liquid oxygen to supply a brief puff of pure oxygen directly via a nasal cannula each time a breath is drawn. Most of the crew, including myself eschew use of the system, allowing our body to adapt to the stresses of high altitude. But a number of units are available in the rack if you need them.

To make the test as stringent as possible I observed each object without oxygen first. After spending the entire day at altitude as well as waiting for sunset, it had been well over ten hours since I had breathed full pressure air. I observed several objects, M51, Omega Centauri, M8 & M20, M81 & M82, and M4, all of which I am very familiar with and observe regularly with 'scopes big and small. I made particular note of what features I could, and could not see with the small refractor.