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Photographer’s Note

An old photo for today's post.
This is the sun rising over the lake Onatrio on a warm August day with the silhoutte of Toronto donwtown on the horizon. I also tried to capture the gradient of sky changing from the red at the horizon and blue at top. Lake ontario looks a bit frozen due to the slow shutter speed.

Urban Legend?: Pollution colours the sky
Another thing that you should also consider while watching this sky is that this colouration is caused by the deeply reddened sun shining from below the horizon onto a high stratum of dust particles and aerosols. So now can you also see all the pollution over the big city of Toronto.

What I have written above is very far from the truth. It was just to arose your emotions, and to remind you guys that sometimes it is a good idea to confirm the facts and not act from the emotions.

It is often said that dust and anthropogenic pollution causes brilliant hues of colours at dawn and dusk. But I wonder why the large cities—such as NYC, London, Mexico City or New Delhi are not celebrated as mecca for surises/sunset colours.

BACKGROUND
1. The colours we see in the sky are the result of scattering, refraction, and diffraction of sunlight by particles in the atmosphere, especially small particles such as air molecules.
2. Particles smaller than the wavelength of visible electro magnetic spectrum, cause greater selective scattering than the bigger particles.
3. Shorter wavelengths of Violet and Blue get scattered more than the longer wavelengths of Red and Orange.

Farther the light travels through the atmosphere, the redder it becomes. Blue light is always scattered the most due to its short wavelenght, but during sunset and sunrise, all of blue light gets scattered at the horizon and this causes only yellow, orange or red light to reach the ground.

The overall scattering produced by most of the pollutants in the urban smog is not strongly wavelength-dependent. The pollutants are much bigger than the wavelengths of colours in the visible light and scatter all the colours. This subdues the colours reaching the observer dramatically. The vibrant oranges and reds of clean atmosphere give way to pale yellows and pinks when pollutants fill the air.

In a nutshell: Pollution can cause the brilliant hues at sunrise and sunset but most of the times this is not the case.

PS: Just wanted to share some scientific trivia with today's post. I just could not write a note simpler than this explaining the phenomenon, Please forgive me if it was too much and correct me if you think I missed something.

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Additional Photos by Sarju Sooch (sarju) Gold Star Critiquer/Gold Star Workshop Editor/Gold Note Writer [C: 1126 W: 52 N: 1270] (5308)
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