Ah, South Dakota. A transition state between the lush prairies and farmlands to the east, and the arid mountains to the west. A bit of both co-reside in this state, and tonight I find myself in a stretch of farmland where the grass has been harvested into giant tootsie-rolls of hay and left at random locations in the field. The mosquitos are fierce, a sure sign of nearby water sources that feed these fields. I do not have my mosquito suit, having left it at home, the land of ten thousand lakes, certain it would not be needed elsewhere.
But I have found another windmill artifact, this one apparently still serving its original purpose, pumping water from the aquifer below to the surface where it can be put directly to agricultural use. Perhaps the catch trough is the source of some of these mosquitos!
There is no wind to make the carnivores work for their blood meal, they land with impunity on any moist skin, and all of my skin is moist tonight. The temperature is 65 degrees, and the dewpoint is the same!
The windmill is about a quarter mile in from the road. I pull off to the side at the field access, an open gate and a vehicle bridge over the gulley. I don’t dare drive into the field, this is not my domain, but I am willing to lug my equipment into place, taking several trips for the tripods, cameras and batteries (to allow the dew heaters to prevent the lenses fogging).
There was not a whisper of breeze, but whatever wind had previously been blowing had left the windmill blades facing south, a fortuitous placement for my composition. I had long wanted to make a direct superposition of the windmill on the North Star, to have the startrails perfectly circumscribe the fan of blades, and here was my chance! I set up the cameras and was surprised where they had to be placed. After a moment I realized that this was exactly right. At this latitude, Polaris was at 450 elevation, the cameras needed to be very low and aimed high to get the composition and angles to work. Even with my wide-angle lenses, the cameras hugged the ground to get the view I wanted.
On my knees to set the tripods, aim the cameras, set the dew heaters, focus and aperture, I finally opened the shutters. I could relax for a while. The exposure time was going to be 80 minutes, exactly one-eighteenth of a day. I had determined this time by counting the number of blades on the windmill, 18. It was a detail that only a mathematician could appreciate, but I have long had suspicions that there are underlying mathematical principles to the esthetic response. I could indulge my intuition in this farmer’s hayfield.
I looked around at the hayfield and realized that I was now surrounded by a thick fog. I could not see more than a few yards in any direction. So this is what happens when the air temperature falls below the dewpoint! I was well aware of the condensation that happens when a lens, radiating heat into space, drops its temperature: it fogs! And so here was an example of the air itself, not just a glass or metallic object, dropping below the dewpoint. Fog!
I experienced a moment of fear. I was out in the middle of some field, I could not see, and I was not sure where my car, or even the road was. Worse, this would ruin the pictures I was taking. But looking up, the sky above was clear. I was in a circular container of fog with the top still open. I could not see any farmhouse lights, my innate sense of direction is poor, but I had the stars to guide me!
If I was not familiar with the sky I would have remained a little frightened, cocooned by a featureless mist with no pointer back to my home base, the car. Instead, I felt somewhat protected. I couldn’t see the traffic on the road, but then again, they couldn’t see me. Their headlights couldn’t penetrate to my camera setup, and no one would wonder what I was doing in the middle of this field. The sky above was open, and my pictures were progressing just fine.
Knowing that I had been traveling north on the road, with the field on the right, I took the steps west, leaving my cameras behind in the fog, until I encountered the road, then north until I found my parked car. I was back at my base camp. I now had a problem. How do I get back to the cameras when their exposure time was up?
My GPS tracker was the answer. I set a waypoint at my car’s location, and then headed back into the fog with the navigation device to find my cameras, this time by “dead reckoning”. I had only a sense of their direction relative to the car and so I set off hoping to see the silhouette of the windmill in a reasonable range. If I didn’t find it, I could always return to the car by aiming for its waypoint, and try again. The GPS signals have no trouble penetrating fog. Fortunately, I found the cameras on my first foray. In a truly worst case, I would have had to wait til morning for the fog to burn off in order to find them. The exposures would have been long ruined, but I would have recovered my equipment.
With markers at both ends of my route, I could now make my way back and forth through the night, each time wandering a slightly different route, but always ending up on target.
Eventually however, the sky covered up completely and even my guiding stars could not be seen. I’m glad this didn’t happen earlier in the evening, before I had my GPS markers set. I would not have been able to find the car so easily. As silly as it sounds to be lost in a hayfield, it would have been a frightening experience. As I packed up and ferried my gear back to the car, following the GPS breadcrumbs, I contemplated the situation I had encountered. My windmill whiteout was a personal lesson in the loss of orientation that explorers experience when they meet more dangerous whiteout conditions. I would advise modern explorers to bring their GPS units!