The “Golden Hour” is that time after sunrise and before sunset when the sun is close to the horizon and its light is considerably more diffuse than when the sun is higher in the sky. In the middle of the day, when the sun is higher in the sky, the light is typically much harsher with deep shadows and bright highlights yielding images with high contrast that, to many, is much less appealing. It is also harder for the camera sensor to record the full brightness range of the scene.
Conversely, with the sun lower in the sky, the shadows are not deep and the camera is better able to capture the full range of the light levels. Further, the lower angle can dramatically enhance the texture and dimensionality of the scene.
When “painting with light”, the time of day can turn a contrasty scene lacking in depth into something with rich tones and fascinating texture that is something special.
Compare these two images of the Grand Mosque in Abu Dhabi, the one on the left was taken just after noon while the one on the right was taken about 15 minutes before sunset.
For even more drama, try shooting during the “Blue Hour“.