[Thebox (OP)]

If the sky is blue because of scattering caused by atmosphere, then why is the atmosphere not blue at ground level where the atmosphere is more dense?

you have it wrong!

[evan_au]

I believe this has been quite adequately explained to you previously in threads in "New Theories".

why is the atmosphere not blue at ground level where the atmosphere is more dense?

It is.

Stand at ground level on a clear day, and look up. The sky is blue, due to scattering by dust in the atmosphere.

Now fly in a U2 spyplane above 70,000 feet. You don't need to wait for a clear day, since you are now above the clouds (and, indeed, above most of the atmosphere). The sky is almost black above you, as there is little scattering of light by dust particles. The sky is blue around and below you, as there is enough dust in the atmosphere as you look through a great depth of it.

Now fly in the International Space Station. You don't need to wait for a clear day, since you are now above the atmosphere. The sky is black, as there is no atmospheric dust particles* to scatter the light. You can see a band of blue light around the Earth, where the atmosphere scatters sunlight.

See: https://www.nasa.gov/multimedia/imagegallery/image_feature_1529.html

* There is also some faint Zodiacal Light, from dust which is in orbit around the Sun, and outside Earth's atmosphere. This light is so faint that human eyes can't really pick up any color in it.

[Thebox (OP)]

I believe this has been quite adequately explained to you previously in threads in "New Theories".

why is the atmosphere not blue at ground level where the atmosphere is more dense?

It is.

Stand at ground level on a clear day, and look up. The sky is blue, due to scattering by dust in the atmosphere.

Now fly in a U2 spyplane above 70,000 feet. You don't need to wait for a clear day, since you are now above the clouds (and, indeed, above most of the atmosphere). The sky is almost black above you, as there is little scattering of light by dust particles. The sky is blue around and below you, as there is enough dust in the atmosphere as you look through a great depth of it.

Now fly in the International Space Station. You don't need to wait for a clear day, since you are now above the atmosphere. The sky is black, as there is no atmospheric dust particles* to scatter the light. You can see a band of blue light around the Earth, where the atmosphere scatters sunlight.

See: https://www.nasa.gov/multimedia/imagegallery/image_feature_1529.html

* There is also some faint Zodiacal Light, from dust which is in orbit around the Sun, and outside Earth's atmosphere. This light is so faint that human eyes can't really pick up any color in it.

Stand outside on a nice day, look up at the sky and see the blue sky that you say is scattering of the light dues to air molecules. Now observe the space between your eyes and the blue sky, it is colourless although there is air .  According to science light should also then scatter and be blue to the observation at ground level also.
Quite clearly literally speaking, we do not observe blue in the space between the ground and sky.

So according to ''you'' somehow the light stops scattering once it as entered deeper into out atmosphere.



scat1.jpg (58.52 kB . 898x572 - viewed 1495 times)

There is nothing about ''your'' version of a blue sky I find to be true.   The physics involved would be wrong.

[alancalverd]

Worth looking up Rayleigh scattering.  Wikipedia has an excellent article on the subject. Fact is

1. It's not dust but elastic scattering of photons from air molecules.

2. You can detect Rayleigh scattering from small volumes of gas but you need a very long  path length before the effect is visible. It is difficult to do the experiment at ground level because the planet gets in the way and over any reasonable distance there will be a considerable amount of dust, fog, etc.

Your best bet is to set up a white arc light about 200 ft above a frozen lake and observe it on a dark night from around 15 miles distance. The light will appear yellow, with a blue haze around it, just like the sun and sky. I'm pretty sure you could find a suitable  spot in Canada somewhere.

[Thebox (OP)]

Worth looking up Rayleigh scattering.  Wikipedia has an excellent article on the subject. Fact is

1. It's not dust but elastic scattering of photons from air molecules.

2. You can detect Rayleigh scattering from small volumes of gas but you need a very long  path length before the effect is visible. It is difficult to do the experiment at ground level because the planet gets in the way and over any reasonable distance there will be a considerable amount of dust, fog, etc.

Your best bet is to set up a white arc light about 200 ft above a frozen lake and observe it on a dark night from around 15 miles distance. The light will appear yellow, with a blue haze around it, just like the sun and sky. I'm pretty sure you could find a suitable  spot in Canada somewhere.

I look ''up'' and I look ''across,  ''across' being a greater distance than ''up'' to the blue sky.  I really do not think the observation lies of where I observe the blue sky to be.  If you were correct then the astronaut would also see a blue sky directly beneath him and at ground level looking ''across'' the air should also still scatter light for the entire distance viewed. 
I don't get it, it makes no sense to me that it scatters.  Where is the force feedback in the scattering to compress the radiation to 400nm?

[Thebox (OP)]

air2.jpg (30.98 kB . 898x572 - viewed 1472 times)

[Bored chemist]

Your torch isn't as bright as the Sun.
The path length isn't several miles wide.
You have not done a meaningful experiment.

Why did you even raise the idea when you had been told you would need, at least, an arc  lamp?
Were you trolling?

[The Spoon]

Of course he is. Comments like this 'Where is the force feedback in the scattering to compress the radiation to 400nm?' when he has been told that compression is not involved and crap like 'force feedback' included for good pseudoscience measure.

[evan_au]

Now fly in a U2 spyplane above 70,000 feet.

Since none of us are likely to ride a U2 (especially since they made very few dual-seat versions), I tried the experiment today using the tail camera on an Airbus A380.

At 39,000 Feet Altitude
You are above most of the atmosphere. The air looks blue as you look towards the horizon, but as you look higher, it is darker (fewer molecules to scatter the light)

A380_39000_feet_small.jpg (45.55 kB . 640x459 - viewed 1508 times)
At 15,000 Feet Altitude
The air looks slightly blue as you look towards the top of the picture (more air molecules to scatter the light)

A380_15000_feet_small.jpg (376.92 kB . 2502x1906 - viewed 1508 times)
At a Lower Altitude
I wasn't able to determine the actual altitude, but you are low enough to make out factory buildings on the ground.
The air is fairly uniformly blue above the clouds and higher.

A380_low_for_buildings_small.jpg (49.68 kB . 640x475 - viewed 1501 times)

[Thebox (OP)]

Now fly in a U2 spyplane above 70,000 feet.

Since none of us are likely to ride a U2 (especially since they made very few dual-seat versions), I tried the experiment today using the tail camera on an Airbus A380.

At 39,000 Feet Altitude
You are above most of the atmosphere. The air looks blue as you look towards the horizon, but as you look higher, it is darker (fewer molecules to scatter the light)

blue.jpg (21.59 kB . 898x572 - viewed 1438 times)
At 15,000 Feet Altitude
The air looks slightly blue as you look towards the top of the picture (more air molecules to scatter the light)
 [ Invalid Attachment ]
At a Lower Altitude
I wasn't able to determine the actual altitude, but you are low enough to make out factory buildings on the ground.
The air is fairly uniformly blue above the clouds and higher.
 [ Invalid Attachment ]

Good observation Evan

At 39,000 Feet Altitude
You are above most of the atmosphere. The air looks blue as you look towards the horizon, but as you look higher, it is darker (fewer molecules to scatter the light)

But as you look lower in any of the observations where the air is much more dense than at altitude, the air  looks clear, transparent, like glass.So why is the light  still not scattering at lower altitudes and looking blue?
I have drawn all 3 of your observations in one picture in basic form.


blue.jpg (21.59 kB . 898x572 - viewed 1438 times)

The white represents clear.   The black is also clear.   The blue the sky.

[Thebox (OP)]

it is darker (fewer molecules to scatter the light)

It is not darker, it just looks darker, it is ''light'' in space remember, it is not looking darker it looks clearer.

The visible spectrum is ''opaque'' relative to the transparency of space.

added- I have drew your observation to objective reality of the observation.


correct observation.jpg (39.3 kB . 898x572 - viewed 1479 times)

[The Spoon]

it is darker (fewer molecules to scatter the light)

It is not darker, it just looks darker, it is light in space remember, it is not looking darker it looks clearer.

The visible spectrum is ''opaque'' relative to the transparency of space.

added- I have drew your observation to objective reality of the observation.


correct observation.jpg (39.3 kB . 898x572 - viewed 1479 times)

Only according to your own definitions of the words 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', 'transparency'.

[Thebox (OP)]

it is darker (fewer molecules to scatter the light)

It is not darker, it just looks darker, it is light in space remember, it is not looking darker it looks clearer.

The visible spectrum is ''opaque'' relative to the transparency of space.

added- I have drew your observation to objective reality of the observation.


correct observation.jpg (39.3 kB . 898x572 - viewed 1479 times)

Only according to your own definitions of the words 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', 'transparency'.

Actually nothing to do with me, I do did not create the Universe and made it that way.   It is observational facts not a belief system.

[Bored chemist]

Actually nothing to do with me, I do did not create the Universe and made it that way.   It is observational facts not a belief system.

Well, I'm glad you accept you didn't create the universe.
Can you explain why you feel empowered to create new meanings for words like 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', and 'transparency'?

Certainly, the way you are using them has nothing much to do with their usual meanings.

[Thebox (OP)]

Actually nothing to do with me, I do did not create the Universe and made it that way.   It is observational facts not a belief system.

Well, I'm glad you accept you didn't create the universe.
Can you explain why you feel empowered to create new meanings for words like 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', and 'transparency'?

Certainly, the way you are using them has nothing much to do with their usual meanings.

Ok, I will call it gogi, poki, nanaphal, if it makes you happy.  I am not changing the definitions , I am correcting the semantics. You can still call it dark and light if you like, but it won't change the semantics I provided.

semantics
sɪˈmantɪks/Submit
noun
the branch of linguistics and logic concerned with meaning. The two main areas are logical semantics, concerned with matters such as sense and reference and presupposition and implication, and lexical semantics, concerned with the analysis of word meanings and relations between them.
the meaning of a word, phrase, or text.

[Bored chemist]

Ok, I will call it gogi, poki, nanaphal, if it makes you happy.  I am not changing the definitions ...

OK, that's a start.
Now tell us what those words mean.

They do not seem to mean what 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', and 'transparency' mean.

[Thebox (OP)]

Ok, I will call it gogi, poki, nanaphal, if it makes you happy.  I am not changing the definitions ...

OK, that's a start.
Now tell us what those words mean.

They do not seem to mean what 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', and 'transparency' mean.

Some people are just not that intelligent. The whole point is your semantics and description of darkness, what it means is wrong.   It would still be called darkness, but darkness would be a property of the object rather than the absence of light.

[Bored chemist]

Ok, I will call it gogi, poki, nanaphal, if it makes you happy.  I am not changing the definitions ...

OK, that's a start.
Now tell us what those words mean.

They do not seem to mean what 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', and 'transparency' mean.

Some people are just not that intelligent. The whole point is your semantics and description of darkness, what it means is wrong.  It would still be called darkness, but darkness would be a property of the object rather than the absence of light.

If you want to coin separate words for
"having the property of absorbing all or nearly all of the em radiation in the range about 400 to 700 nm wavelength" and "unillluminated,
that's fine by me. However in English, the word "dark" means both of those, and the word, "darkness" is construed accordingly.

Some people are, it seems not intelligent enough to realise that a word can have two meanings, depending on context.
They then rigidly try to stick to just one of those meanings even when it's not appropriate.
For example, it is dark in my cellar at the moment. Darkness reigns there.
If I go down there and turn the lights on, it will no longer be dark. The darkness will be  expelled.
There are two wooden cupboards there one is made from ebony and the other from birch.
The first is dark, the second is light.
That remains true even if I turn the lights back off again.

[Thebox (OP)]

Ok, I will call it gogi, poki, nanaphal, if it makes you happy.  I am not changing the definitions ...

OK, that's a start.
Now tell us what those words mean.

They do not seem to mean what 'darker', 'light', 'space', 'clearer', 'visible', 'opaque', and 'transparency' mean.

Some people are just not that intelligent. The whole point is your semantics and description of darkness, what it means is wrong.  It would still be called darkness, but darkness would be a property of the object rather than the absence of light.

If you want to coin separate words for
"having the property of absorbing all or nearly all of the em radiation in the range about 400 to 700 nm wavelength" and "unillluminated,
that's fine by me. However in English, the word "dark" means both of those, and the word, "darkness" is construed accordingly.

Some people are, it seems not intelligent enough to realise that a word can have two meanings, depending on context.
They then rigidly try to stick to just one of those meanings even when it's not appropriate.
For example, it is dark in my cellar at the moment. Darkness reigns there.
If I go down there and turn the lights on, it will no longer be dark. The darkness will be  expelled.
There are two wooden cupboards there one is made from ebony and the other from birch.
The first is dark, the second is light.
That remains true even if I turn the lights back off again.

I for one understand the difference a word can have in meanings.    You however still do not understand why it is not dark in your cellar.
Your two cupboards in the light  seem different in appearance , one being light in appearance and the other being dark in appearance.   However when it is dark, both cupboards are the same in appearance,both cupboards are dark in appearance.
The space between you eyes is unaltered in appearance although you ''see'' that space turn dark. 
Darkness what you call with the lights out, is not just the absence of light, it is the original appearance of all objects without enough intensity or magnitude of electromagnetic radiation to produce visible light. ( the visible of a  dark and light cupboard).

  added-
While the lights are on , one of your cupboards appears visibly dark.
When the lights are off, both cupboards appear visibly dark.

In the ''dark'' you can still see the cupboards, but they both appear dark. This gives you the sense that the space is also dark, that bit is an optical  illusion.

[Bored chemist]

You however still do not understand why it is not dark in your cellar.

However when it is dark...

Hang on; you just said it can't be dark down there.
Make up your mind.
Perhaps the problem is that you can't understand that it is, in fact, dark down there.
Shall we set up a poll?