The sky turns a soft blue.
This happens near sunrise or sunset. The sun is far below the ground. It makes the light look pretty. We can see it in the morning or night. Do you like the blue sky?
The sky turns a soft blue.
This happens near sunrise or sunset. The sun is far below the ground. A layer in the air makes the light blue. This blue time can be very short. It can last for many minutes. It can also last for a long time. The blue color can look yellow or red too. Some people like to take photos then. The light is very soft. It makes a calm feeling. It is a pretty time of day.
The blue hour is a special time of day. It happens near sunrise or sunset. During this time, the sky looks mostly blue.
This happens when the Sun is far below the horizon. The horizon is the line where the sky meets the land. The blue color comes from the ozone layer. This is a layer of gas in our air. The ozone layer uses Chappuis absorption. This means it lets blue light pass through more easily.
Blue hour can last from 20 to 96 minutes. The time depends on where you live. Near the equator, the blue hour is very short. This is because the Sun rises and sets at steep angles. Near the poles, the time is much longer. The Sun rises and sets at shallow angles there.
Artists and photographers love this time. The light is very soft. It can make a calm mood. Some people like to take photos of city lights then. They may photograph bridges or big buildings.
The blue hour is a special time of day. It happens during twilight in the morning or evening. During this time, the sunlight looks mostly blue. This light creates a very calm mood. It is not the same as a clear day. A clear day uses something called Rayleigh scattering. The blue hour is different because of the ozone layer.
This blue color happens in a specific way. The Sun must be deep below the horizon. It must be far enough down for Chappuis absorption to work. This is a thing that happens in the ozone layer. The ozone layer absorbs some light. This allows the blue wavelengths to dominate. Red light passes through space during this time. Meanwhile, blue light scatters in the air to reach us.
People use the term blue hour in a casual way. It does not have an official scientific definition. It is not like dawn or dusk. Instead, it refers to a state of natural lighting. This lighting usually happens during the nautical stage of twilight. This stage occurs near sunrise or sunset. Photographers and artists find this time very useful. They like the soft quality of the light.
How long the blue hour lasts can change. It usually lasts between 20 and 96 minutes. The time depends on your place on Earth. Near the equator, the blue hour is quite short. This is because the Sun sets at a steep angle. Near the poles, the time is much longer. The Sun sets at a shallow angle there. In Egypt on June 21, the timing is very specific.
Let us look at the numbers from Egypt. On that day, sunset is at 7:59 PM. The blue hour lasts from 7:59 PM to 9:35 PM. Sunrise is at 5:54 AM. The blue hour is from 4:17 AM to 5:54 AM. The golden hour happens around these times too. Photographers often capture cityscapes or bridges during the blue hour. They like to use artificial lights from buildings. This makes for beautiful photos.
The blue hour is a specific period of twilight in the morning or evening. During this time, the sunlight takes on a deep blue shade. This phenomenon occurs when the Sun is at a significant depth below the horizon. It is a period of natural lighting that usually happens around the nautical stage of twilight. While the term is used commonly, it lacks an official scientific definition. It is distinct from terms like dawn or dusk. Instead, it describes a particular state of light in the atmosphere.
To understand how this happens, we must look at the atmosphere and the Sun. Many people believe the blue color comes only from light scattering. They think the atmosphere simply disperses blue light while scattering red light away. However, the real cause involves a process called Chappuis absorption. This process occurs within the ozone layer. When the Sun is far enough below the horizon, the ozone layer absorbs certain parts of the light spectrum. This absorption allows blue wavelengths to dominate the light we see.
The mechanism of light travel during this time is quite specific. During the blue hour, red light passes through space. Meanwhile, blue light is scattered within the Earth's atmosphere. This scattering allows the blue light to reach the surface of the Earth. If the sky is clear, the blue hour can be a colorful spectacle. The indirect sunlight can tint the sky with yellow, orange, red, and blue. This happens because of how different wavelengths of light behave. Shorter blue rays are more easily diffused than longer red rays.
The duration of the blue hour is not the same everywhere. It usually lasts between 20 and 96 minutes. This length depends on your location on the planet. Near the equator, the blue hour is shorter. This is because the Sun rises and sets at very steep angles. In regions closer to the poles, the period is much longer. In those places, the Sun rises and sets at shallower angles. These different angles change how much time the light spends in the twilight stages.
We can see how these timing changes work by looking at Egypt. On June 21st in Egypt, the sunset occurs at 7:59 PM. During this time, the blue hour lasts from 7:59 PM until 9:35 PM. The sunrise in Egypt on that day is at 5:54 AM. The blue hour begins at 4:17 AM and ends at 5:54 AM. There is also a period called the golden hour. In this example, the golden hour happens from 5:54 AM to 6:28 AM. It also occurs from 7:25 PM to 7:59 PM.
Artists and photographers find the blue hour very important. They value the period for its soft quality of light. The blue color spectrum is most prominent when the Sun is between 4° and 8° below the horizon. Photographers often use this time to create a tranquil mood. It is a favorable time to photograph subjects with artificial light sources. These include buildings, monuments, bridges, and cityscapes. The combination of natural blue light and man-made light can be very striking.
The blue hour connects to several larger scientific and artistic ideas. It is an example of an atmospheric optical phenomenon. It relates to the study of color temperature and light scattering. Understanding the blue hour requires knowledge of the ozone layer and the Sun's position. It also connects to the study of how humans perceive light and color. By studying these moments, we learn more about our atmosphere and the physics of light.
Where will your curiosity go next?
🖼️ Images & Media (1)
More to explore
✨ What else?
Related topics you might enjoy
🔬 Go deeper
More advanced topics to explore
🪜 Step back
Simpler topics to build understanding
What is Nepedia?
A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.