The blue hour (from French l'heure bleue)[a] is the period of twilight in the morning or evening, during the civil and nautical stages, when the Sun is at a significant depth below the horizon and residual, indirect sunlight takes on a predominantly blue shade.The blue hour occurs when the Sun is far enough below the horizon that the sunlight's blue wavelengths dominate. Because "blue hour" is a colloquial term, it doesn't have an official definition similar to dawn, dusk, and the 3 phases of twilight. Rather, it refers to a state of natural lighting that usually occurs at daybreak in the morning and during the last stages of twilight in the evening.
How and When it HappensEdit
The Earth’s post-sunset and pre-sunrise atmosphere solely receives and disperses the sun’s shorter blue wavelengths, which is the reason why the hue of this hour is so blue. On the other hand, the sun’s longer red wavelengths scatter themselves out into space without touching the Earth. 
When the sky is clear, the blue hour can be a colorful spectacle, with the indirect sunlight tinting the sky yellow, orange, red, and blue. This effect is caused by the relative diffusibility of shorter wavelengths (bluer rays) of visible light versus the longer wavelengths (redder rays). During the blue "hour", red light passes through space while blue light is scattered in the atmosphere, and thus reaches Earth's surface. Blue hour usually lasts about 20-30 minutes right after sunset and right before sunrise. For instance, if the sun sets at 6:30 p.m., blue hour would occur from 6:40 p.m. to 7 p.m.. If the sun were to rise at 7:30 a.m., blue hour would occur from 7 a.m. to 7:20 a.m.. Time of year, location, and air quality all have an impact on the exact timing of blue hour. 
Blue Hour PhotographyEdit
Many artists value this period for the quality of the soft light. Although the blue hour does not have an official definition, the blue color spectrum is most prominent when the Sun is between 4° and 8° below the horizon. 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. In order to successfully capture the enchantment of blue hour in your photographs, consider these guidelines:
• Plan accordingly: Due to the fact that blue hour is short, come prepared with your camera settings in the right place. It is recommended to use a sun calculator to find out when the Sun will be at the perfect angle at your chosen shooting location.
• Adjust light levels: Utilize a higher ISO than you would during normal daylight hours.
• Utilize wide aperture: With the help of a wide aperture you can make lights (such as street lamps) appear soft and glowy.
• Utilize a tripod: Using a tripod will allow you to maintain a strong and steady stance when capturing your perfect blue hour image.
• Shoot in RAW: It is recommended that you shoot in RAW if you are using a DSLR/ any other type of advanced camera. Shooting in RAW will allow you to maintain and enhance the beautiful cool tones of blue hour.
• Don’t forget to play: Remember, blue hour occurs twice a day, every day. Feel free to experiment with your aperture, flash, ISO, and shutter speeds!
Camera Settings and SubjectsEdit
• Exposure: light is limited during blue hour. Because of this, your shutter speed will need to be a bit slower than it usually is in order to let the maximum light into your lens. It is optimal to use a slow shutter speed and a small aperture for landscape photographer during this hour.
• Manuel Focus:It is recommended that you shoot in manual focus during blue hour. this is because shooting in auto focus will give your camera a difficult time finding something to focus on due to the low and limited light of blue hour.
• Portraits: If you’re in the mood for some unique and creative portraits, blue hour is a great time for you. Don’t neglect using a fast shutter speed when shooting portraits at this time, you’ll want to avoid blurry images. Make sure your model’s face is illuminated enough during this time, shooting near street lights or other external sources of light can help with this.
• Landscapes: Landscapes are perfect for blue hour photography! However, the key is in finding the right one. Find a setting that will look flattering under the conditions of blue hour. You can begin by finding settings that already have light in them, like a lit up bridge, the moon, street lamps, or city lights reflected on a body of water can work well during this hour.
- Verfaillie, Roland (2011). L'heure Bleue. San Francisco: Purple Onion Press. p. 5.
- "The Blue Hour". timeanddate.com. Retrieved 6 April 2019.
- "What is the blue hour? Learn about this magic time between daylight and darkness". mnn.com. Retrieved 7 April 2019.
- "Blue Hour – Magic Hour". timeanddate.com. Retrieved 16 October 2017.
- "What is the blue hour?". earthsky.org. Retrieved 7 April 2019.
- Harman, Christina. "Guide to Blue Hour Photography". loadedlandscapes.com. Retrieved 7 April 2019.
|Wikimedia Commons has media related to Blue hour.|
- Blue hour mobile application (iOS, Iphone/iPad)
- bluehoursite.com: Everything about Blue Hour and Night Photography (news, articles, tips and calculator)
- Twilight Calculator, Golden Hour/Blue Hour table
|This science article is a stub. You can help Wikipedia by expanding it.|