Offline Pinky

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How do sunsets work?
« on: November 29, 2018, 08:49:10 AM »
I have read these
https://wiki.tfes.org/Sun
https://wiki.tfes.org/The_Setting_of_the_Sun
https://wiki.tfes.org/Magnification_of_the_Sun_at_Sunset

And I am more confused than ever.

The second Wiki-page says that sunset is due to the Sun moving so far away that its observed size shrinks beyond the resolution of the eye.

But the third Wiki-page says that the observed size doesn't shrink despite the Sun moving further away, because of light-scattering in the atmosphere.

If the Sun maintains its observed size despite moving further away, then why does the Sun disappear eventually? Why is there a cutoff? Why does the Sun maintain a certain observed size throughout the day and then the observed size suddenly shrinks within a few minutes and it's gone?

How far away is the Sun when it goes from non-shrinking to shrinking?



The second Wiki-page mentions some non-transparent atmospheric layer that dims sunlight, but that doesn't explain the sharp cutoff and it doesn't explain why the Sun-disc shrinks asymmetrically while maintaining its radius.

Re: How do sunsets work?
« Reply #1 on: December 02, 2018, 05:55:36 PM »
Because the earth is an oblate spheroid. A globe. Easy answer.

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Offline junker

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Re: How do sunsets work?
« Reply #2 on: December 02, 2018, 07:22:05 PM »
Because the earth is an oblate spheroid. A globe. Easy answer.

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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #3 on: December 02, 2018, 08:08:37 PM »
If you feel that it isn't clear, feel free to help rewrite it to make a better distinction between the actual sun and the visible sun.

Offline Spingo

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Re: How do sunsets work?
« Reply #4 on: December 04, 2018, 09:05:11 PM »
If you feel that it isn't clear, feel free to help rewrite it to make a better distinction between the actual sun and the visible sun.

Even after reading the Wiki on the sun I’m still not sure what you are reffering to when you mention, the actual sun and the visible sun, for is the actual sun not also visible?

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Offline rabinoz

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Re: How do sunsets work?
« Reply #5 on: December 04, 2018, 09:37:49 PM »
If you feel that it isn't clear, feel free to help rewrite it to make a better distinction between the actual sun and the visible sun.
Sorry to be so late posting this, but maybe you could explain why there is any "distinction between the actual sun and the visible sun" other than some slight refraction when the sun appears on the horizon?

I do tend to believe what I see, unless given a good reason why that is incorrect and sunsets I see look like this:

Sun near setting at Weipa
               

Sunset at Weipa
Not only that but the apparent size of the setting sun is the same as when overhead apart from a slight reduction in height:

The real sun[/i] certainly appears to move across the sky without changing in size as in these photos taken from a video made by Matrix Decode with very good photos of the sun through a filter (an arc welder's glass) shown  at a number of times of day from 12:00 PM to 7:00 PM on 9/March/2016 in Malaga, Spain.

Here are three afternoon ones from his video and they do an excellent job of showing that the sun size does not change!
   

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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #6 on: December 04, 2018, 10:39:32 PM »
You posted what appears to be light projected onto the atmosphere. Please explain why the outer edges of the sun are dimmer than its center.

Re: How do sunsets work?
« Reply #7 on: December 04, 2018, 10:42:58 PM »
You posted what appears to be light projected onto the atmosphere. Please explain why the outer edges of the sun are dimmer than its center.
Are you saying those are not pictures of the sun?

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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #8 on: December 04, 2018, 10:46:11 PM »
I do believe that is the sun. I am asking why the outer edges of the sun are significantly dimmer than the center of the sun like a projection on a movie screen.

Here was the image that was posted:



Here is another example, of a solar eclipse as seen through an eclipse filter:



The brightest areas are at the center of the sun.

Projetor Hotspot:



Source: Hotspotting or brightness inhomogeneity

The hotspot is also true for laser beams.

Again, I ask, why should this be true for the sun?
« Last Edit: December 04, 2018, 11:27:03 PM by Tom Bishop »

Re: How do sunsets work?
« Reply #9 on: December 04, 2018, 11:25:22 PM »
Sunsets for the same reason that sunrises occur. The Earth is spinning and this means that different parts of the surface turn towards (sunrise) and then away (sunset) from the direction of the Sun. 


Regarding mael_cookies post, why are people warned for contributing information about a thread which is correct?  A concise answer without any waffle.  What's the problem?

Re: How do sunsets work?
« Reply #10 on: December 04, 2018, 11:31:27 PM »
Tom, regarding your question...
Quote
I do believe that is the sun. I am asking why the outer edges of the sun are significantly dimmer than the center of the sun like a projection on a movie screen.


The answer I have provided elsewhere but I will say it again.  This is a well known phenomenon we see in 'white light' called limb darkening.  The Suns 'surface' is actually a layer of its atmosphere known as the photosphere. Looking in the centre of the visible disk we are looking directly down into the lower levels of the photosphere where the plasma is hotter than in the upper levels. Hotter is always brighter on the Sun.  At the edges we are looking more obliquely across the upper layers only where the plasma is cooler and hence darker.  This gives the effect of limb darkening.


When observing the Sun at specific wavelengths such as Ha and CaK we are looking at light emissions coming from the chromosphere (sphere of colour) The chromosphere is above the photosphere and is normally invisible without special filters apart from during a total solar eclipse.  If you look closely at photos showing totality you will notice the reddish prominences looking like flames arcing away from the solar limb. These are coming from the chromosphere.   

The chromosphere, though much hotter than the photosphere is emitting light only at specific wavelengths and therefore the darkening effect is much less.
« Last Edit: December 04, 2018, 11:39:35 PM by LoveScience »

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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #11 on: December 04, 2018, 11:33:59 PM »
Lets see what Dr. David H. Brooks of George Mason University has to say about this:

https://www.sciencedaily.com/releases/2017/08/170803091936.htm

Quote from: David H. Brooks
The Sun's surface, the photosphere, has a temperature of around 6000 degrees, but the outer atmosphere, the corona -- best seen from Earth during total solar eclipses -- is several hundred times hotter. How the corona is heated to millions of degrees is one of the most significant unsolved problems in astrophysics.

"Why the Sun's corona is so hot is a long-standing puzzle. It's as if a flame were coming out of an ice cube. It doesn't make any sense!"

The sun's corona is the wispy 'atmosphere' the sun, seen only during the moment of Total Solar Eclipse, or with a coronagraph.

6000 degrees is also significantly different compared to 15 million degrees Kelvin for the inner center of the sun.

Why are the outer layers of the sun significantly dimmer than the center? As admitted, it is a mystery that doesn't make any sense under the current theories of the sun.
« Last Edit: December 04, 2018, 11:44:48 PM by Tom Bishop »

Re: How do sunsets work?
« Reply #12 on: December 04, 2018, 11:43:55 PM »
As regards Davids comments about the very hot corona I completely agree with him but that has nothing to do with the limb darkening effect we see in white light.  The Sun has an upper photospheric temperature of about 5500K and a core temp of 15 million K as he says.  We know the core temp from the fact that hydrogen burning (into helium) by a method known and the P-P chain is taking place. In higher mass stars the CNO cycle is more dominant. The light we see from the Sun today is the byproduct of nuclear fusion reactions that took place between 100,000 and 1 million years ago. What are initially released as gamma ray photons lose energy from interactions in the convection and radiation zones within the Sun. The loss of energy converts them into X ray photons, then UV photons until eventually they enter the optical band by the time they reach the photosphere at which point they escape into space. The journey to Earth then takes 8 minutes and 20 seconds travelling at 299,792,458 m/s.

The corona is the outermost layer of the solar atmosphere and lies beyond the chromosphere.  It is divided into the inner and outer corona and its total extent out into the solar system is not exactly known. 

Surely it is the mysteries of science that creates the fascination of it. If we knew everything about the Sun there would be no incentive to carry on studying it. We are very fortunate in having the Sun at such close distance from us compared with all the other stars. It allows us to study a G2 type main sequence star in the mid term of its evolution. 
« Last Edit: December 04, 2018, 11:54:19 PM by LoveScience »

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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #13 on: December 04, 2018, 11:50:06 PM »
Dr. Brooks says that it is an unsolved mystery that doesn't make sense under the theories of the RET sun.

Will you show that he is wrong and that it does make sense?

Or, will you continue to present unsolved mystery as fact that we need to disprove?

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Offline markjo

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Re: How do sunsets work?
« Reply #14 on: December 04, 2018, 11:50:40 PM »
Tom, how is that relevant to how sunsets work in FET?
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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #15 on: December 04, 2018, 11:59:14 PM »
Tom, how is that relevant to how sunsets work in FET?

The failure of science to explain this is entirely relevant.

See the third link in the OP: https://wiki.tfes.org/Magnification_of_the_Sun_at_Sunset

Re: How do sunsets work?
« Reply #16 on: December 05, 2018, 12:03:01 AM »
The failure of science to explain what exactly?  Science is about learning and working towards understanding what we don't yet know. Or is that irrelevant to you as well?

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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #17 on: December 05, 2018, 12:08:51 AM »
The failure of science to explain what exactly?  Science is about learning and working towards understanding what we don't yet know. Or is that irrelevant to you as well?

It is not irrelevant to me at all.

Science is working towards better understanding. I agree. We explain the inconsistent brightness better in our Wiki as being a cause of a projection upon the atmoplane, whereas RET cannot explain it.

If you want to challenge it, then we expect you to explain this under your Round Earth Theory.

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Offline stack

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Re: How do sunsets work?
« Reply #18 on: December 05, 2018, 12:21:06 AM »
The failure of science to explain what exactly?  Science is about learning and working towards understanding what we don't yet know. Or is that irrelevant to you as well?

It is not irrelevant to me at all.

Science is working towards better understanding. I agree. We explain the inconsistent brightness better in our Wiki as being a cause of a projection upon the atmoplane, whereas RET cannot explain it.

If you want to challenge it, then we expect you to explain this under your Round Earth Theory.

I wouldn't say that "projection upon the atmoplane" is an explanation. As evidenced by?

Also curious why you're citing a paper funded by NASA, wouldn't that immediately discredit it in your eyes?

"The study, published in Nature Communications and funded by the NASA Hinode program".

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Offline Tom Bishop

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Re: How do sunsets work?
« Reply #19 on: December 05, 2018, 12:25:44 AM »
I wouldn't say that "projection upon the atmoplane" is an explanation. As evidenced by?

As evidenced by the sun. I am waiting for you to provide a better explanation.

If you cannot explain this under your model, then I would expect you to stop pretending that RET does provide the better explanation for this.