Star Trails

Moraine Valley
Rocky Mountain National Park
Photograph by Tom Atwood

Star trails in long exposure photographs like this one are caused by the Earth's rotation. I have found the trails begin to form after the camera's shutter has been open for more than 30 seconds. In photos of 30 seconds or less, the stars look like stars. In this photo, a one minute and 20 second shot, you can see how the stars begin to streak. At midnight, the full moon is rising behind the camera, lighting the very highest peaks of the Rockies and making the sky almost blue. The moonlight has not yet lit the valley, where one of my favorite rivers in the world, the Big Thompson, flows through it. Shutter: 80 seconds; Aperture: f/1.8; ISO: 100; Focal length: 35 mm.