Ouray Star Trails

Ouray, Colorado creates the foreground of a well balanced photo because it’s perfectly centered between two beautiful mountains. I’ve visualized taking this composition of star trails above Ouray for the past few years, but there were either nightly clouds that blocked the stars, or I wasn’t there at the right time. I finally captured this shot this September on my fall colors trip through the San Juan Mountains.

In simplified terms, this photo is a continuous 120 minute exposure. During long exposures like this the Earth spins causing the stars to naturally trail across the photo. Star trails occur in any direction of the night sky during long exposures, but they only trail in perfect circles around Polaris (The North Star), which is why I positioned Polaris in the upper center of the photo.

To be technically specific, this photo was created by setting the camera to continuously shoot 144, 50-second exposures that were then “light stacked”. If the photo had actually been a single 120 minute exposure it would be brightly overexposed with no discernible details. The light stacking process analyzed all 144 exposures and kept only the “new” pixels from each image that were brighter than in the previous exposures to create one composite image. Light stacking is done in software, and some cameras do it internally and output the completed composite image. Through this method the base image which is properly exposed is retained, and only new light is added to the image as it appears. In the case of this photo, the new light that was added appears as the star trails and cars driving on the streets.

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