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Today (July 5th, 2019 just before 8 pm KST), along the Han River in Seoul, the surface of the sun could be viewed with my naked eye (no protection needed), and this was safe on the eyes. It appeared much redder and it wasn't bright at all. Also, there was no visible "fog" that blocked the view of the sun in my vicinity.

I am curious about the conditions needed to create this phenomenon A possible use-case of an answer could mean the possibility to better predict when I should go view the sunset over the Han River in Seoul. It's beautiful!

Past Related Topics

Why can I look directly at the sun during a sunset but not at noon?

This is different from my question as, while you can still look at it, it is still slightly harmful to your eyes. It can still create some visual artifacts in your vision after you stop staring for even a few seconds.

The sun I saw today at sunset was not bright at all. You could stare at the sun for minutes, tens of minutes, etc without any visual impairments. Also, the sun was red in color.

There appears to be at least one more additional condition needed to produce the visual I saw today.

My Thoughts

Just to be clear, this seems to go beyond the physics of the standard sunset. To me, there seem to be 3 atmospheric conditions that are playing their part in this phenomenon. The first 2 will give you the standard sunset with its beautiful colors.

  1. Rayleigh Scattering.
  2. The longer distance light travels along the Horizon.
    • This enhances Rayleigh Scattering and gives the colors of the sunset.
  3. ???
    • Either this enhances Rayleigh Scattering more along the horizon (enhances #2)
    • Or it's a separate phenomenon completely
      • When combined with #1 and #2, allows people to view the surface of the sun without protection!

More Background Information

  1. I have seen this phenomenon a few times before in Seoul.

    • Phenomenon never occurred in the US in my hometown for me
      • Hometown is farther north than Seoul.
      • Harbin, China would be a similar latitude.

  2. I have never seen this phenomenon during the winter.

    • It's possible it has happened, but I didn't see it!
    • It's only occurred in the Spring and Summer for me.

  3. While the afternoon was thicker in air pollution, I believe around sunset the air pollution nearby was much more clear.

    • Around this time (if UTC conversion were correct), there was a thicker air pollution mass around China and the northern part of the Yellow Sea.
      • Sun sets in the West, and any air conditions to the west could affect the sunset.
      • Is that in line-of-sight? Did the air pollution reach higher in the atmosphere around China? With line-of-sight, that would be around 10 - 60km in the air over the Yellow Sea and China.

Analysis

With #1 and #2 directly above, the longer distance that light travels along the horizon during (1) the sunset and (2) the winter in the Northern Hemisphere doesn't seem to play a big part. Otherwise, I should see this a lot in the winter around sunset. I don't, and I never have.

Can air pollution be clear nearby, yet block all the bright light rays farther away?

Photo

Here is a photo that can help show the conditions that were present at the time. Please note that the sun appears much brighter in this picture than it was in-person. The sun was actually really dull red. As you can see, there were clouds, but I am trying to find maps that show the cloud coverage around that time, as I don't believe it was thick.

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  • $\begingroup$ Check the weather at 8pm - timeanddate.com/weather/south-korea/seoul/historic?hd=20190705 $\endgroup$
    – Christopher Rucinski
    Jul 5, 2019 at 21:52
  • $\begingroup$ As a child in the 1960's in Los Angles, the effect you are discussing was very common. It was primarily due to air pollution in combination with moist air from the Pacific, or so I was told. I don't know the exact pollutants but believe a significant portion was from automobile exhaust. $\endgroup$
    – user824
    Jul 5, 2019 at 23:51
  • $\begingroup$ @Friddy while the picture looks "heavily" cloudy, it was more clear than it looks. I have seen instances where I could look at the sun directly due to cloud cover and other highly visible material, but that was less apparent during this time. There appeared to be little in the way in my near vicinity. $\endgroup$
    – Christopher Rucinski
    Jul 6, 2019 at 6:06
  • $\begingroup$ @Christopher_Rucinkski, In LA the air was clear but with high relative humidity. It was my understanding that the moister air reacted with the pollutants. Although not a scientific article this one marketplace.org/2014/07/14/la-smog-battle-against-air-pollution outlines the type of pollution. See this about photochemical smog energyeducation.ca/encyclopedia/Photochemical_smog. $\endgroup$
    – user824
    Jul 8, 2019 at 15:27

1 Answer 1

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I am familiar with this phenomenon. In London, in winter 1947, I remember being able to see sunspots with the naked eye. The sun was very orange, like the one in your photo. The reason I was able to see sunspots was,of course, that the London sky was polluted with fumes and the winter sun was low on the horizon, so the rays had a greater thickness of atmosphere to penetrate. Much of the short wavelengths were filtered out, while the longer, redder wavelengths were able to get through. Much the same thing seems to have happened when you took this photograph of Seoul. It is common knowledge that red wavelengths penetrate foggy or hazy atmospheric conditions better than shorter wavelengths.

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  • $\begingroup$ I do highly believe that there is a 3rd condition that needs to be met, and that condition is particles in the air. Due to the curvature of the Earth, the effects of fog, haze, and distant clouds along the 400km+ line-of-sight path. Again, the clouds nearby were much thinner than they appear in the picture. I looked at some weather 400km to the west-north-west of Seoul and found that high clouds were present and very possible in the line of sight. With the Incheon, Korea and Seoul weather, it's possible these all added up to show this dull red sun?? $\endgroup$
    – Christopher Rucinski
    Jul 6, 2019 at 6:27
  • $\begingroup$ dizzib.github.io/earth/curve-calc/… $\endgroup$
    – Christopher Rucinski
    Jul 6, 2019 at 6:28

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