The other day I was trying to figure out the meaning of the word twilight. I thought I knew what it meant. I thought it only referred to the time after sunset until it gets completely dark. And then I heard the word used in reference to the time right before sunrise.
Twilight is the time between dawn and sunrise, and the time between sunset and dusk. Sunlightscattered in the upper atmosphere illuminates the lower atmosphere, and the surface of the Earth is neither completely lit nor completely dark. The sun itself is not actually visible because it is below the horizon. Due to the unusual and romantic quality of the ambient light at this time, twilight has long been popular with photographers and painters, who refer to it as "sweet light" or the "blue hour", after the French expression l'heure bleue. Twilight is technically defined as the period before sunrise and again after sunset during which there is natural light provided by the upper atmosphere, which does receive direct sunlight and reflects part of it toward the Earth's surface.
That phrase, the blue hour, just sounds so cool to me. I took my camera out at the blue hour a lot this past summer and so here above is one image from the blue hour, from back in July.