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South Arc Trails There's not much night-time when the Earth is at the Summer Solstice of its annual orbit. Startrail pictures are limited to the few hours remaining after the last glow of twilight, but before the onset of early dawn. The sky is dark enought to avoid fogging the film only after what is called "astronomical twilight", a condition where the sun falls below the horizon by 18 degreees. It must remain below the horizon by this margin over the duration of the exposure. The late sunset, early sunrise and summer ecliptic leave only a few precious hours to make startrail pictures. I had gotten a late start on this night. I drove west, watching the sun set, followed by the crescent moon. I was looking for a site away from city lights and the ubiquitous rural security lights. I eventually got out of range of radio towers with their flashing warnings to aircraft, and the nearest farmhouse seemed behind the windbreak trees at the horizon. But it was well after midnight. In the motion picture business there is an admonition when shooting on location to not "burn daylight". Don't waste time when the scene requires the light of a specific time of day. Well, I had burned "nightdark" by not being ready to open my shutter at the moment after astronomical twilight ended. And regardless of when I start my exposure, it must end before astronomical dawn begins: at 3:30 AM, or the brightening sky will wash out the any startrails that had been recorded. The result shows the gentle startrail arcs whose center is the invisible south pole, the lowest ones fading into the skyglow of rural farmhouses and distant communities. The arcs flatten out and become straight as one approaches the celestial equator, then arc upward for stars whose apparent route takes them around the North Star. The Milky Way, a visually bright band that I briefly mistook for clouds as I stood under the summer sky, is spread into a faint mottled texture as a startrail backdrop to this scene.
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