The "blue hour" is one of my favorite times to take photographs.

Wikipedia defines the blue hour as:

"The blue hour is the period of twilight each morning and evening when the sun is a significant distance below the horizon and the residual, indirect sunlight takes on a predominantly blue hue. This effect is caused by the relative diffusability of short blue wavelengths of light versus the longer red wavelengths. During the blue "hour" (typically the period is about 40 minutes in length), red light passes straight into space while blue light is scattered in the atmosphere and therefore reaches the earth's surface. Because of the quality of the light, this period is treasured by artists. Photographers call it sweet light."

Here's an example of how the blue hour impacts a photograph. This was my last photo shoot from my recent trip through the Capital Cities of the Southeast.

Sunset was 4:08 PM in Charleston, West Virginia. With all of the cloud cover, there wasn't much of a sunset to photograph. At 4:16 PM, the sky was still gray. I was beginning to doubt whether any colors would appear at all that night:

Downtown AtlantaDowntown Atlanta (east side) at dusk from the Jackson Street Bridge over the Freedom Parkway NE in Atlanta, Georgia on December 2, 2014. And here's another one from Charleston, South Carolina:

Ravenel BridgeSunset at the Arthur Ravenel Jr. Bridge across the Cooper River (connecting downtown Charleston to Mount Pleasant) in Charleston, South Carolina on December 7, 2014

Finally, here's a recent one from Providence, Rhode Island:

Waterplace ParkWaterplace Park, the Woonasquatucket River and downtown Providence from the Martin Luther, Jr. Bridge at Francis Street in Providence, Rhode Island on July 24, 2015.