The "Blue Hour" refers to the period of twilight when the sun is just below the horizon, creating a soft, diffused light. This time occurs twice a day, in the morning before sunrise and in the evening after sunset. The sky takes on a deep blue hue, which is ideal for photography and outdoor activities, as it provides a unique and serene atmosphere. During the Blue Hour, the contrast between artificial lights and the natural blue sky can create stunning visual effects. This phenomenon is often sought after by photographers and artists, as it enhances the beauty of landscapes and cityscapes, making it a popular subject in works by Vincent van Gogh and many contemporary photographers.