Blue hour photos that is. “The blue hour occurs when the Sun is far enough below the horizon so that the sunlight’s blue wavelengths dominate due to the Chappuis absorption caused by ozone. Blue hour usually lasts about 20–30 minutes right after sunset and right before sunrise. Photographers cherish blue hour for the tranquil mood it sets. When photographing blue hour it is recommended to capture subjects that have artificial light sources, such as buildings, monuments, cityscapes, or bridges.” – Wikipedia
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