Iridium Flare Over the Colorado River

October 03, 2010

Sunlight at night

Photographer: Sean M Sabatini
Summary Author: Sean M Sabatini

The photo above showing a brilliant iridium flare illuminating the nighttime sky was captured over the Colorado River, below Lake Mead, Nevada on April 4, 2002. In the span of less than a minute, a barely visible iridium satellite becomes the brightest object in the sky, and then quickly fades away. Because of the curvature of the Earth, high-altitude objects can often be lit by sunlight even though night has fallen on the surface below. Just as high clouds can remain beautifully sunlit well after the sundown,  satellites in low earth orbit (a few hundred miles up) can abruptly reflect sunlight for a few seconds, several hours after sunset or before dawn.  The Iridium satellite series is the showiest of all man-made satellites. Their highly-reflective antennae are notorious for catching the Sun and causing dramatic flares as they pass overhead. Under a dark sky the effect is especially dazzling. On this night, the surrounding landscape is partially lit by the waning crescent Moon, providing another less startling example of reflected sunlight. Note that the glitter path reflection on the river is coming directly off the iridium flare, which had a magnitude of about -6 and was 12 degrees above the horizon. The Moon, at the time the picture was snapped, was only 16 percent illuminated. 

Photo details: digital scan from 1600 Fuji color film; 34 second exposure; 50 mm lens; f/1.8. Photo taken at 3:07 a.m. before the start of astronomical twilight. The camera is looking east-southeast.