There is an amazing phenomenon that occurs on clear evenings after sunset. As sunlight is scattered in the upper atmosphere it illuminates the lower atmosphere and produces luminous blue skies. It is known as the blue hour, even though it normally only lasts for a short period of time.
In early March I was hoping to capture Harrisburg at twilight for a photography contest. So one evening I made the hour drive and arrived just as the sky turned a brilliant blue. Within five to ten minutes the sky began to darken and the moment was gone, but lives on in this image.