I thought the Blue Hour only occurred in France, perhaps because it was here in Paris that I first appreciated it. But in fact, the Blue Hour can occur anywhere on earth, either in the city or in the countryside. In Spain it’s called La Hora Azul.
During twilight, when the sun descends between 4 and 6 degrees below the horizon, the Blue Hour can happen. A lot depends on temperature, the amount of haze, moisture and pollutants in the air, but basically the blue waves of light from the sun diffuse into the atmosphere. They remain visible to us, while the reddish waves escape into space. I suppose this is why the sky is blue in the first place. But the blue of Blue Hour is much more intense, cold, vivid and saturated than the normal color of a blue sky.
The Blue Hour has inspired writers, musicians, filmmakers and photographers as well as painters. The multi-disciplinary Belgian artist Jan Fabre produced a series of drawings called The Hour Blue. Click here to see a video of his collaboration with the Kunsthistorishces Museum in Vienna.