People are roasting this person for asking a dumb question. But I think this is a valid query and the answer is actually pretty cool.
Unfortunately, you usually get a response like this.
This is accurate. But not very explanatory. "It's how light works" just feels a bit condescending.
We need to Bill Nye this shit.
The first thing you need to know is that light competes with light. And the brightest light is always the victor.
And this phenomenon is not specific to cameras. Our eyeballs also play in the light vs light competition.
Every person with a mobile phone has already seen this effect. What happens when you look at your phone on a really sunny day?
You can't see shit.
The sun is so overwhelmingly bright that it is reflecting light off the screen that is much brighter than the light being emitted from the phone.
However, newer phones are starting to have screens that are extremely bright. Up to 3000 nits in some cases. They are able to emit light brighter than the sun's reflection.
What happens to our eyes when we go outside on a sunny day?
Our pupils get as small as they possibly can. Smaller pupils let in a lot less light. And when they are that contracted, we can only register really really bright things.
But if we are in the dark, our pupils get super big. They allow in a bunch more light. And after we adjust to the dark, we can see really really dim things.
If our pupils stayed contracted and we looked at a starry sky, it would be as blank as the phone screen on a sunny day. You can even test this with an eye patch. Go into a very bright room and keep one eye covered for about 20 minutes. Then go outside and look at the sky with each eye. One eye will see stars and the other will not.
And this should give you a clue as to how light pollution works. Light bounces off stuff in the atmosphere. And when a city shoots a bunch of light upward, that light reflects back down and is much brighter than the stars.
The brightest light always wins.
Most stars are just incredibly dim. You need to be in a very dark environment in order to see them shine. You need them bigass pupils fully activated. And cameras need either a very large aperture (lens pupils), or a very long time interval to see them.
The sun is so so soooo bright. Many thousands of times brighter than distant stars. And the moon is also very bright. Especially if you are on or near the surface. The properties of moon dust, the regolith, are a near perfect diffuse reflector. Which is why astronauts struggled to see and photograph stars during their moon excursions.
If they opened up their camera apertures and did a long exposure, they'd just get a blank white frame.
There are dozens of photos in which that exact thing happened.
This is exactly what happens if you accidentally shine a flashlight directly into your eyes.
But if we ever have a moon mission during lunar night, those astronauts are in for a starry treat. They won't have any atmosphere to absorb starlight. So they'll be able to see the Milky Way, in all its glory, with just their naked eyes.
also, apparently, when you are at the bottom of a deep well during daytime, and the sun is NOT directly in line-of-sight over it, you CAN see the Stars.
I really hope this doesn't come off as embarrassing, but this is actually a myth.
But it is a really cool ancient myth from one of Aristotle's essays written 2400 years ago.
And I think it is kind of neat that intellectuals from back then were trying to understand and figure out how light works. And it is impressive that a myth has lasted this long.
The problem is that the sky is a giant light source. A pretty bright one, in fact. People often forget that the sky is a giant hemisphere of scattered light because the sun is so overwhelming in comparison. It's just so much dimmer than the sun, it gets outshone on sunny days.
But you can see the sky being a light source on snowy days. If you look at photos of snow, you'll notice all the shadows are tinted blue.
That's the sky getting into the nooks and crannies where the sun don't shine.
So if you were deep in a well, you'd just see the blue sky.
HOWEVER, if you were to create a deep hole on the moon during lunar daytime, you could totally see stars. You'd be in a dark environment, your pupils would open up, there is no atmosphere to scatter light from the sun, and the glare of the surface wouldn't compete with the starlight.
Aristotle was on to something, he just chose the wrong celestial body.
Naomi is an anti-vaxx dipshit and not a great person.
But I think this question was asked in good faith and is also a perfectly valid query.
Moon nomenclature can be a bit confusing. People will reference the far side of the Moon and the dark side of the Moon and conflate the two.
From our perspective, there is a near side and a far side. The "near side" is always facing Earth. And people sometimes think the side facing away from us is also the "dark" side of the Moon.
But the far side is not always in darkness. Only when we see a full moon is it dark.
Astronomers have tried to update the terminology to lunar day and lunar night, but that hasn't really caught on as popular vernacular. It's hard to undo Pink Floyd's influence.
All of this is to say, it is easy for people to get confused about the far side of the Moon being illuminated by the Sun. It's quite common to imagine it as in perpetual darkness.
But lunar night is not completely in a void of darkness. The light from the universe does very dimly illuminate the lunar backside. And while traditional optics aren't easily able to see the Moon's butt, NASA does have a special UV camera that surveys the lunar night.
It's called the "Lyman-Alpha Mapping Project."
They love their clever acronyms.
I've seen people also confused about the lighting in this photo.
The Sun is directly behind the Moon, yet the left side seems to have light wrapping around to the lunar night side.
And the reason for this makes my light-loving heart full. Because light is light and it works the same way in space as it does in my studio.
This phenomenon is called "Da Vinci glow" or earthshine. The Sun is bouncing light off the Earth, and it is reflecting onto the side of the Moon. And even though it is usually too dim to see without a very long exposure, this eclipse was able to reveal it.
Here is what earthshine looks like to human eyes adjusted for darkness.
And here is a brightened, long exposure example.
It's literally just this on a cosmic scale...
There is also moonshine, which is more than just a legally dubious beverage.
You may have already seen an example.
The left is exposed as our eyeballs would see it. And the right is brightened with long exposure and a high gain setting.
The Sun is behind the Earth, but it is shining light off the Moon and giving very dim illumination to the night side.
The Moon is a big retroreflector. You have seen a different form of retroreflection when you are driving at night and the highway signs light up as you pass. Your headlights are shining directly back at you.
The special properties of Moon dust give it a near-perfect diffuse matte reflection. And when the Sun is in the right position, it acts similarly to our car headlights and the light shines back in our direction.
A studio reflector needs to be angled just right to shine the light exactly where you want it. The angle of the light is like a bumper shot in billiards.
The Moon scatters light in all directions like a typical matte surface.
However, a non-retroreflective matte reflection on a sphere typically has a bright center and then graduates into darkness around the edges. But the Moon's super matte retroreflection maintains brightness across almost the entire surface area.
So even though the Moon is quite small compared to the Earth, its regolith creates a powerful reflection of the Sun's light. You'd think a full moon would be twice as bright as a half moon, but this retroreflective surge makes the Moon roughly 10 times brighter.
If the Moon weren't such a dusty bitch, moonlight would be dimmer and that nighttime photo of the Earth may not have been possible.
