On their way to the Earth's surface, they encounter atmospheric particles such as dust and water droplets, which filter the sunlight, ultimately making it less bright. When the Sun is just above the horizon, its rays impact the Earth at a low angle and they have to travel through more of the Earth's atmosphere before they reach us. What is the blue hour? Why Is the Light Golden? The Sun's angle in your city-click on the table By this definition, the golden hour begins with civil dawn in the morning and ends with civil dusk in the evening. However, the warm sunlight that is characteristic for the golden hour most likely occurs when the Sun is between 6 degrees below and 6 degrees above the horizon. Rather, it refers to a state of natural lighting that is most common around sunrise and sunset. The moments when 99% of people see sunlight Definition of the Golden Hourīecause the golden hour is a colloquial term, it doesn't have an official definition similar to dawn, dusk, and the 3 phases of twilight. The warm sunlight makes the golden hour a favorite among photographers and filmmakers. Business Date to Date (exclude holidays)Ī golden retriever enjoys the golden hour on a beach in Vietnam.I have actually tested this ozone explanation of blue hour, using the Precomputed Atmospheric Scattering code to render two versions of the same scene: one for atmosphere with an ozone layer and another without any ozone. So the ozone absorption effect is also less pronounced.Īnd at twilight the Earth's shadow prevents light from passing through troposphere, making the only light visible scattered from the stratosphere and above, and this light in large part gets there through the ozone layer, traversing it through the long dimension. Thus ozone has much smaller effect on daytime sky.ĭuring sunset much of the sunlight passes through the troposphere, getting redder, while getting scattered into the observer more than from the stratosphere where most of the ozone layer is located (due to higher concentration of air molecules). For the same reason it's reddened less by Rayleigh scattering, leaving more blue light to make the sky blue. Here's spectral cross section of ozone absorption in the visible(+NIR) range - the Chappuis band:Ĭould you explain why the effect of ozone is more important after sunset? Why doesn't this change the story during sunset, or during the day?ĭuring the day sunlight passes much smaller distances through the atmosphere, thus is absorbed less. See in particular my answer for the question at Chemistry.SE: What exact color does ozone gas have?. Ozone doesn't absorb blue light (much): on the contrary, it absorbs red light much more, thus making the sky look blue. Wikipedia states very strongly that explanations of this in terms of Rayleigh scattering are wrong, and that the real explanation is the absorption of blue light by ozone. What's the right explanation for the blue hour? And if the blue light is reemitted, then the effect of ozone should qualitatively be very similar to the effect of Rayleigh scattering, since it's just another scattering route that favors blue light, leading us back to the original puzzle. If the blue light is not reemitted, then this just amounts to having less blue light, so it can't explain why the blue hour is more blue. But it doesn't explain why that would create the effect. Why would the color go from blue to golden to blue again? However, it seems this can't be the full story, because photographers know that after sunset, there is a so-called blue hour where the color of the sky becomes a deep blue again. During the sunset, the length of atmosphere the light from the Sun has to travel through becomes so long that the blue is depleted, giving the sky a golden color. During the day, blue light from the Sun is scattered towards us from all directions, causing a blue sky. Rayleigh scattering affects blue light more. There's a great story about why the sky is blue during the day, and turns golden during sunsets:
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