Comments and questions about the
APOD on the main view screen.
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APOD Robot
- Otto Posterman
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by APOD Robot » Tue Aug 06, 2024 4:05 am
Storm Cloud Over Texas
Explanation: What makes this storm cloud so colorful? First, the
cloud itself is composed of millions of tiny droplets of water and ice. Its bottom is almost completely flat -- but this isn't unusual.
Bottom flatness in clouds is generally caused by
air temperature dropping as you go up, and that above a specific height, water-saturated air condenses out water droplets. The
shape of the cloud middle is caused by a water-droplet-laden column of air being blown upward.
Most unusual, though, are the orange and yellow colors. Both
colors are caused by the cloud's water drops reflecting sunlight. The orange color in the cloud's middle and bottom sections are reflections of a nearly
red sunset. In contrast, the yellow color of the cloud's top results from
reflection of light from a not-yet-setting Sun, where some -- but less --
blue light is being scattered away. Appearing to
float above the plains in
Texas, the
featured impressive image of a dynamic
cumulonimbus cloud was
captured in 2021 while investigating a
tornado.
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Eclectic Man
- Ensign
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Post
by Eclectic Man » Tue Aug 06, 2024 2:01 pm
What a wonderful photograph. Interesting and informative explanation. However, one minor quibble,
the cloud itself is composed of millions of tiny droplets of water and ice
Well, yes, but clouds are tenuous things and contain approximately 1000 droplets per cubic centimetre. So a cubic kilometre of cloud (not unusual) would contain approximately 10
18 water droplets, rather than mere 'millions'.
(
https://www.wtamu.edu/~cbaird/sq/2014/0 ... y%20spaced. )
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bls0326
- Science Officer
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Post
by bls0326 » Tue Aug 06, 2024 4:15 pm
I live in this area. We do get some spectacular weather (sunsets, thunderstorms, tornados) but this picture is most impressive. Great shot!!
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johnnydeep
- Commodore
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by johnnydeep » Tue Aug 06, 2024 7:00 pm
APOD wrote:In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.
Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
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Ann
- 4725 Å
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by Ann » Wed Aug 07, 2024 3:55 am
johnnydeep wrote: ↑Tue Aug 06, 2024 7:00 pm
APOD wrote:In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.
Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?
Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.
Ann
Color Commentator
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johnnydeep
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by johnnydeep » Wed Aug 07, 2024 12:36 pm
Ann wrote: ↑Wed Aug 07, 2024 3:55 am
johnnydeep wrote: ↑Tue Aug 06, 2024 7:00 pm
APOD wrote:In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.
Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?
Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.
Ann
Maybe it's a density thing? Denser air will reflect more blue light simply because there are more molecules to do the deflecting?
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
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Ann
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by Ann » Wed Aug 07, 2024 1:24 pm
johnnydeep wrote: ↑Wed Aug 07, 2024 12:36 pm
Ann wrote: ↑Wed Aug 07, 2024 3:55 am
johnnydeep wrote: ↑Tue Aug 06, 2024 7:00 pm
Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?
Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.
Ann
Maybe it's a density thing? Denser air will reflect more blue light simply because there are more molecules to do the deflecting?
I think that is just right, Johny!
Ann
Color Commentator
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Chris Peterson
- Abominable Snowman
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by Chris Peterson » Wed Aug 07, 2024 2:06 pm
Ann wrote: ↑Wed Aug 07, 2024 3:55 am
johnnydeep wrote: ↑Tue Aug 06, 2024 7:00 pm
APOD wrote:In contrast, the yellow color of the cloud's top results from reflection of light from a not-yet-setting Sun, where some -- but less -- blue light is being scattered away.
Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?
Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.
Ann
We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.
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johnnydeep
- Commodore
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by johnnydeep » Wed Aug 07, 2024 3:39 pm
Chris Peterson wrote: ↑Wed Aug 07, 2024 2:06 pm
Ann wrote: ↑Wed Aug 07, 2024 3:55 am
johnnydeep wrote: ↑Tue Aug 06, 2024 7:00 pm
Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?
Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.
Ann
We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.
And there's no air density factor affecting how much blue light it scattered?
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
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Chris Peterson
- Abominable Snowman
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by Chris Peterson » Wed Aug 07, 2024 4:00 pm
johnnydeep wrote: ↑Wed Aug 07, 2024 3:39 pm
Chris Peterson wrote: ↑Wed Aug 07, 2024 2:06 pm
Ann wrote: ↑Wed Aug 07, 2024 3:55 am
Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.
Ann
We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.
And there's no air density factor affecting how much blue light it scattered?
Obviously, lower density air scatters less light. But in what way would that impact these images? There isn't much variation in density between the bottom and top of the clouds. And what we see in the air itself is a product not of density variation, but of path length.
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johnnydeep
- Commodore
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by johnnydeep » Wed Aug 07, 2024 6:38 pm
Chris Peterson wrote: ↑Wed Aug 07, 2024 4:00 pm
johnnydeep wrote: ↑Wed Aug 07, 2024 3:39 pm
Chris Peterson wrote: ↑Wed Aug 07, 2024 2:06 pm
We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.
And there's no air density factor affecting how much blue light it scattered?
Obviously, lower density air scatters less light. But in what way would that impact these images? There isn't much variation in density between the bottom and top of the clouds. And what we see in the air itself is a product not of density variation, but of path length.
Ok, thanks.
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
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Ann
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Post
by Ann » Thu Aug 08, 2024 4:02 am
Chris Peterson wrote: ↑Wed Aug 07, 2024 2:06 pm
Ann wrote: ↑Wed Aug 07, 2024 3:55 am
johnnydeep wrote: ↑Tue Aug 06, 2024 7:00 pm
Ok, this seems to be implying that the red bottom color is ALSO due to blue light being reflected away. If so, why is more blue light reflected away lower down than in the upper clouds?
Hmm... don't ask me to explain how or why, but I note that the same thing happens to the sky during sunsets.
Ann
We don't see the top of the clouds. We see the bottom and we see the sides facing us. The bottoms are lit by the setting Sun and the sky around it, which is why they are orange. The sides facing us are in shadow, so they are the color of the sky (as are shadows on the ground), so they look blue or white. The edges are forward scattered light (as opposed to reflected) which shows the same color as the Sun itself. None of the cloud coloration is strongly impacted by whatever the atmosphere between the viewer and the cloud is doing.
I can' figure out why the colors are so well separated. The orange part of the cloud appears to be the same shade of peach, although admittedly the very bottom part appears to be a tad redder. And the yellow part of the cloud is almost the same shade of lemon overall.
Ann
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Chris Peterson
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by Chris Peterson » Thu Aug 08, 2024 12:42 pm
Ann wrote: ↑Thu Aug 08, 2024 4:02 am
I can' figure out why the colors are so well separated. The orange part of the cloud appears to be the same shade of peach, although admittedly the very bottom part appears to be a tad redder. And the yellow part of the cloud is almost the same shade of lemon overall.
Ann
Well... I'll note that the image was taken with a phone, and the sad reality in this Instagram obsessed world is that the default camera settings on most phones (or even the deliberately chosen ones) are frequently "vivid" or a similar one that boosts clarity and saturation. The colors here look to me like they've been pushed beyond the actual visual appearance of the phenomenon somewhat. So I wouldn't look too deeply into the exact colors, just the color range and general transition trends.