Is it possible to perceive a difference between sunrise and sunset?

Pendant (n).
One who,
by correcting others,
gives himself (or herself)
just enough rope
by which to hang.

Me, 1993

Having been a ‘pendant’ (by the above definition) for many years, I’ve gotten into the habit of questioning my own preconceptions about yIn ‘u’ Hoch je (Life, the Universe, and Everything). Colour me pretentious, but I actually believe that this is a Good Thing, especially in this (anti-)social media dominated era, where misinformation and disinformation foster bad memes and ‘FAKE NEWS!!!!1’. Being constantly on guard for the possibility that one’s view of reality could be wrong is, surely, a useful attitude. Training an open mind is, I believe, the route to wisdom.

‘Sunray Meadow’ by @lacharpenta
Used with permission (click to embiggen)

So when my friend Goldie, in response to last week’s wibblette, adamantly asserted that @lacharpenta’s photo, above, was definitely taken in the morning, not the evening, I wondered how he could be so certain. I began to doubt my own belief that it was impossible to determine whether the Sun in this photo was rising or setting. So, I decided to DuckDuckGo the question ‘Is there any difference in sunlight between morning and evening?‘.

The results were very interesting. I learned about Rayleigh scattering, Mie scattering and the Tyndall effect – but only a little: most of it went straight over my head (if you’ll pardon the pun).

One of the persuasive arguments I discovered was that human activity during the day kicks up pollutants into the atmosphere, so that, come evening, the Sun’s light is scattered more. This atmospheric dirt settles overnight, so the morning and evening skies can appear different.

And one thing I found particularly fascinating was that we can perceive a difference because of how our eyes work.

I was, however, unable to come up with a definitive answer.

Here’s an extract from one article this search revealed:

According to atmospheric physicists David Lynch and William Livingston, the answer is “yes, and no.”

All “twilight phenomena” are symmetric on opposite sides of midnight, and occur in reverse order between sunset and sunrise, the authors note in “Color and Light in Nature” (Cambridge University Press, 2001). That means there’s no inherent, natural cause of a major optical difference between them. However, two human factors break their symmetry.

The first is in our heads. “At sunset, our eyes are daylight adapted and may even be a bit weary from the day’s toil,” Lynch and Livingston write. “As the light fades, we cannot adapt as fast as the sky darkens. Some hues may be lost or perceived in a manner peculiar to sunset. At sunrise, however, the night’s darkness has left us with very acute night vision and every faint, minor change in the sky’s color is evident.” In short, you may perceive more colors at dawn than at dusk. [Red-Green & Blue-Yellow: The Stunning Colors You Can’t See]

Human activities also drive a divergence between them. “At sunset the sky is full of pollutants and wind-borne particles,” the authors write. “During the night, winds die down, smog-producing urban activity eases and the atmosphere cleanses itself. The dawn is clearer than any other time of day.”

‘Do Sunrises Look Different from Sunsets?‘, Live Science, 2012

If there is a difference between the appearance of skies near dawn and dusk due to the increase of pollution in the air during the day (and I don’t doubt that), then, surely, this effect will be greater in urban areas, due to smog.

Couple that with the concept of ‘normality’: it’s a natural tendency to believe that what experience teaches each of us to expect (in all manner of things) is ‘normal’ for everyone else, too. So, if you live in an urban area, you’ll be used to this greater dawn/ dusk sky difference effect… and perhaps come to believe that this is the same everywhere, and for everyone. Although I grew up in ‘The Smoke’ (London), for the last two decades I’ve lived in a rural area, where there’s never any smog. As I write this, the Sun is going down, and the sky seems to me just as blue as it was this morning.

So, perhaps it’s unsurprising that Goldie should both consider that this particular photograph is ‘definitely’ a morning one and find it hard to understand why I can’t see that. He’s absolutely right that this photo was shot in the morning: I got that straight from the horse’s mouth.

Hey there Yetan. Your friend is correct, it's a morning view to the east. Its funny, morning and evening pics have a different vibe, often to do with the colour of the sky, I think, mornings cooler/evenings warmer tones.

— laird of the debatable lands (@lacharpenta) October 15, 2022

But being right about this image doesn’t mean that it’s always possible to tell a rising Sun from a setting one in every case; there are too many variables. Thanks to Goldie, I’m now better prepared to guess this of a similar photo, but I hope that I will always refrain from stating my opinion with certainty.

The Goon Show: morning and evening greetings