When I was hiking a week ago, I had a couple of interesting revelations about using flashlights at night.
Both happened in the pre-dawn hours. The first revelation came second chronologically, on Sunday morning. It was mostly overcast, so I wasn't motivated to spend lots of time looking at the sky. So I went down to the stream early to fetch water to boil for my morning coffee. The path is quite steep and fairly long, so I was using my headlamp. And I mused — not for the first time — how a flashlight cuts you off from the world around you. When you're in the woods on a moonless night, you can't see much without a flashlight, but you can see equally well (or poorly) in every direction. The flashlight creates a bubble of light around you. Inside that bubble, everything is clear. Outside, it's totally black.
Many sites on the web review flashlights, and it's a little startling how much they assume that brighter flashlights are always better. In the backcountry that's simply not true. The last thing you want to do is to blow your dark adaptation completely.
So is the faintest possible flashlight best, then? No, that's not true either — as my experience the previous morning had shown. On Saturday morning, when it was clear, I did want to see the sky as much as possible, and didn't want to destroy my dark adaptation. So I climbed down from the boulder where I was perched using just my red flashlight.
Frankly, it was pretty scary. The highest point of the boulder is perhaps 10 feet off the ground — not a long enough drop to kill, but enough to be quite unpleasant. On the side I climbed up, there was a rock pile reaching almost to the top — but not quite within reach of my foot as I lowered myself off the boulder. I knew quite well that there was solid ground just inches below my foot, but the red flashlight wasn't bright enough to illuminate it. So I had to trust my memory, and jump blind. Needless to say, it worked. But I'm not sure that preserving my dark adaptation was worth the brief moment of terror.
What does this have to do with astronomy? I'll get to that in my next blog.