By Maria Merola אריאל © Copyright Double Portion Inheritance, August 2002-2023
The phenomenon occurs because thinner clouds are transparent, and the light from the Sun or the Moon is relatively very bright. Our eyes and camera sensors are unable to distinguish the part of the Sun/Moon which is obscured by the thin clouds from the part which is unobstructed by clouds.
Parts of the clouds outside the Sun/Moon disc are still visible, making it appear as if they are behind the Sun/Moon. We can simulate this using a light source and a few sheets of semi-transparent material, like old camera films.
If the light source is bright enough, then the transparent material would appear as if it is not there, giving the illusion it is behind the light source.
Explained: Why Clouds Appear Behind the Sun and Moon
Sometimes clouds appear to be behind the sun or the moon in photos and videos, like the example above (source). This confuses people, as the sun is 93 million miles away, so it’s impossible for clouds to be behind it. Some people take this as evidence that reality is an illusion, or the Earth is flat.
But what’s really going on here?
Basically, the sun is extremely bright. So bright, that in most photos and videos it just appears as something at the maximum brightness the camera can handle, so just appears as flat white. If there’s something in front of it that’s transparent enough to let though a lot of the sunlight, then that bit will be less bright, but still higher than the maximum brightness the camera can handle.
So, the camera will still see it as the same as the rest of the sun, bright white. This creates the illusion that partially transparent objects go behind the sun.
The upper cloud that goes “behind” the sun is transparent, so the sun shines through it.
The middle and lower clouds are less transparent, so they partially block the sunlight enough to fall below the maximum brightness the camera can handle, hence they are visible, and seem to go in front (which is what all the clouds are really doing)
In the above image, the power lines are not transparent.
But because they are out of focus, that has the same effect (thin out of focus objects are effectively transparent blurs)
Here is a simulation of this I just did, a work light behind a sheet of cardboard, and a hole covered in paper representing the sun. The old negatives represent clouds, and the antenna represents power lines, etc.
Firstly, with the “sun” off.
The “clouds” (partially transparent film strips) look like they are behind the “sun.”
Zoomed in, the cloud still goes “behind the sun.” The antenna also seems to go behind (although less so, almost like it's piercing the sun.
Here’s a really simple version of the experiment that anyone can do, you need:
*A darkish room.
*A single sheet of white paper.
*Three inches or so of Scotch “magic finish” tape, (or similar thin semi-transparent non-shiny material).
*A bright light.
*Some dark background.
*Put the tape on the side of the paper, so it's half on, and half off.
*View it against the dark background.
*Notice the tape is highly visible against the dark background.
Put the tape in the side of the paper, so it’s half on and half off. View it against the dark background. You will notice that the tape is highly visible against the dark background.
This is not a camera effect. This is exactly how it is seen by the naked eye.
The topic also has some practical application, in that I’m “scanning” in some 16mm negatives by photographing them with the work light behind them. So it’s like I’m photographing these partially transparent in front of a bright light. This is analogous to photographing clouds.
I need to adjust the exposure, so that “the whites” in the negative are as bright as possible without going over the maximum that the camera can handle. If the light were too bright, then we would see areas of flat black, and too dim areas of flat white (it’s negative so reversed). Careful adjustment leads to the best dynamic range.
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