Wednesday, February 4, 2015

An Awesome Sight: the Red Sunset

I was in a discussion once where a theist said that the beauty of the sunset was reason to believe in God.  I certainly don't deny that a sunset can be beautiful, and I feel the same sense of awe that he does when I see it.  But that sense of awe does not translate to "God made all this".  I marvel at nature.  Nature holds many wonders and secrets to be discovered.  And that's beautiful.

What is nature's way of making the brilliant red color of the setting sun?  It's called Rayleigh scattering.  Basically, light passing through the atmosphere gets scattered by particles in the air, and the lower wavelength light experiences more scattering than the longer wavelength light.  Lower wavelength light is blue, and longer wavelength light is red.  So the blue light is more diffuse, and gets scattered throughout the whole sky, which makes it look ... (wait for it) ... blue.  The effect is more pronounced when the sun is near the horizon, because there is more atmosphere that the light must pass through.  The red light light is less diffuse because it is scattered less.  So when we look at (or near) the sun we see more direct light, which is red.  That's the effect of Rayleigh scattering in a nutshell.

I told my theist friend about this phenomenon, and he insisted that I was wrong, and that I don't know what I'm talking about.  He happens to be an amateur astronomer, and he thinks he has the correct scientific explanation: diffraction.  I showed him a couple of articles that explain it, but he continued to insist that I was wrong.  Since that time, he has made numerous statements to the effect that I know nothing about science.  Now that hurts, coming from someone who obviously understands it less than I do.  It's not so much that I'm bothered by his opinion, but that he has the respect of other theists who are even more scientifically ignorant, and they tend to believe him rather than me.

I have declined to discuss my own education and credentials in that forum for a couple of reasons.  One is that I don't want to reveal personal information any more than I have to.  But a bigger reason for me is that I despise people who base their argument on their degrees or their credentials.  If your argument is correct and valid, it shouldn't matter who you are or what credentials you have.   But since my theist friend still won't listen to me, I'll just give him a little argument from authority.  I hope this is enough to convince you, buddy.

At sunrise and sunset, when the path through the atmosphere is longer, the blue and green components are removed almost completely leaving the longer wavelength orange and red hues we see at those times. The remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange. The removal of the shorter wavelengths of light is due to Rayleigh scattering by air molecules and particles much smaller than the wavelength of visible light (less than 50 nm in diameter). -

Atmospheric nitrogen and oxygen scatter violet light most easily, followed by blue light, green light, etc. So as white light (ROYGBIV) from the sun passes through our atmosphere, the high frequencies (BIV) become scattered by atmospheric particles while the lower frequencies (ROY) are most likely to pass through the atmosphere without a significant alteration in their direction. -

Sunsets are reddened because for sun positions which are very low or just below the horizon, the light passing at grazing incidence upon the earth must pass through a greater thickness of air than when it is overhead. Just before the sun disappears from view, its actual position is about a diameter below the horizon, the light having been bent by refraction to reach our eyes. Since short wavelengths are more efficiently scattered by Rayleigh scattering, more of them are scattered out of the beam of sunlight before it reaches you. Aerosols and particulate matter contribute to the scattering of blue out of the beam, so brilliant reds are seen when there are many airborne particles, as after volcanic eruptions. -

most of us know that white light – like sunlight – is composed of all the colors of the rainbow. Tiny molecules in our atmosphere cause light to scatter. That’s why our sky looks blue: it’s because the atmosphere scatters the bluish component of white sunlight. And it’s why the sun looks reddish when it’s near the horizon. -

A phenomenon called Rayleigh scattering causes light from the Sun to bounce off tiny particles in the atmosphere and scatter in different directions. Sunlight consists of many different colours: from red, which has the longest wavelength of all visible light, through to violet at the blue end of the spectrum, which has the shortest wavelength. Due to this short wavelength, blue light is scattered more effectively than other colours, and this is why the sky normally appears blue to us.
At sunrise or sunset, however, when the Sun is low on the horizon, the light rays must pass through more of the atmosphere – and therefore bounce off more molecules – than at other times of day. This means that more blue light gets scattered away before the light reaches your eyes. Other colours – such as red, orange and yellow – can therefore continue to pass through the atmosphere unaffected, creating beautiful colours at the start and end of the day. -

No comments:

Post a Comment