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APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 4:06 am
by APOD Robot
The Belt of Venus over Mount Everest
Explanation: You've surely seen it, but you might not have noticed it. During a cloudless
twilight, just before
sunrise or after
sunset, part of the atmosphere above the horizon appears slightly dark and off-color. Called the
Belt of Venus, this transitional band between the dark
eclipsed sky and the bright day sky can be seen most prominently in the direction
opposite the Sun. Straight above,
blue sky is normal sunlight reflecting off the atmosphere, while near the horizon the clear sky can
appear more orange or red. In the
Belt of Venus, the atmosphere reflects more light from the setting (or rising) Sun and so
appears more red. Featured here, the
Belt of Venus was photographed over several
Himalayan mountains including, second from the right,
Mount Everest, the
tallest mountain on
Earth. Although usually
not mentioned, the belt is
frequently caught by accident in other photographs.
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 5:39 am
by Ann
Let's try to make head or tails of the colors of today's APOD, shall we?
Let's begin with the Earth's rising (or setting) shadow during sunset (or sunrise). Well, shadows in clear weather on the Earth tend to be blue, right?
Shadows on white snow are blue, because they are lit up by the blue sky only. During twilight, when sunlight becomes increasingly reddened - because more and more shortwave light is filtered away, and the light that reaches us directly from the Sun is more and more deeply yellow-orange, or even red - shadows and sunlight on the ground can create an obvious blue/yellow effect.
You may have seen this sort of cloudless sunset:
I wanted to show you this sort of sunset because the sky color deepens to a clear deep red at the horizon. Not all sunsets are like this. Many are just
yellowish.
The twilight sky over San Diego is quite dark blue, but the horizon is vividly yellow and red. The color of the Belt of Venus is much paler and more diluted, but the general color scheme is the same. Yellowish sky is followed by pink (not red) sky. And then it is all interrupted by the rising (or setting) blue shadow of the Earth.
I have question. Is that billowing gray stuff seen in the middle of the APOD actually fog?
Ann
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 12:05 pm
by VictorBorun
Ann wrote: ↑Mon Jun 26, 2023 5:39 am
Let's try to make head or tails of the colors of today's APOD, shall we?
Let's begin with the Earth's rising (or setting) shadow during sunset (or sunrise). Well, shadows in clear weather on the Earth tend to be blue, right?
Shadows on white snow are blue, because they are lit up by the blue sky only. During twilight, when sunlight becomes increasingly reddened - because more and more shortwave light is filtered away, and the light that reaches us directly from the Sun is more and more deeply yellow-orange, or even red - shadows and sunlight on the ground can create an obvious blue/yellow effect.
You may have seen this sort of cloudless sunset:
I wanted to show you this sort of sunset because the sky color deepens to a clear deep red at the horizon. Not all sunsets are like this. Many are just
yellowish.
The twilight sky over San Diego is quite dark blue, but the horizon is vividly yellow and red. The color of the Belt of Venus is much paler and more diluted, but the general color scheme is the same. Yellowish sky is followed by pink (not red) sky. And then it is all interrupted by the rising (or setting) blue shadow of the Earth.
I have question. Is that billowing gray stuff seen in the middle of the APOD actually fog?
Ann
They seem to say that this APOD looks in the direction opposite to low Sun's disk.
Thinking about the colours of the sky, I try to have 2 things in mind:
1) from the centre of the disk of Sun there must be rings of red, scarlet, orangish, slightly yellow, grey, slightly cyan, bluish, indigo, violet, gaining in area and losing in brightness, summing up to total illumination to which we adapt as to current white
2) those rings are far from being concentric circles' rings. Each ring gets wider where it passes near horizon and narrower where it passes high. That explains why yellow zone is narrow above the San Diego sunset and wide at horizon
But what is the Belt of Venus, I am at loss
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 1:10 pm
by Guest
So why do they say Everest is the highest peak? It doesn’t look that way. Oh, they must say it depends on where the “mountain” begins.
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 2:09 pm
by Chris Peterson
Guest wrote: ↑Mon Jun 26, 2023 1:10 pm
So why do they say Everest is the highest peak? It doesn’t look that way. Oh, they must say it depends on where the “mountain” begins.
It is not based on where the base of the mountain is. Everest is the peak that is highest above mean sea level. You can't look at a range of mountains and reliably say which peak is highest based just on appearance. A closer mountain will appear relatively higher than a more distant one.
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 2:17 pm
by De58te
Guest wrote: ↑Mon Jun 26, 2023 1:10 pm
So why do they say Everest is the highest peak? It doesn’t look that way. Oh, they must say it depends on where the “mountain” begins.
This is a photographic illusion. Although Everest and Lhotse are adjacent, Makalu is actually 19 kilometers away from Everest. Here Makalu happens to be closer to the camera viewpoint so looks slightly taller.
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 4:24 pm
by fkingery
Beautiful photo of the Himalaya range. I spent a couple of months there many years ago mapping the geology in view of the then evolving theory of "Mountain Building and The New Global Tectonics."
One comment: in the photo, I believe Lhotse and Everest are mislabeled. Should be the other way around.
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 5:05 pm
by epalmer
The red and blue colors of the sky do not involve reflection at all, but rather Rayleigh scattering by air molecules. Light at the blue end of the spectrum is scattered more efficiently, dropping off as the fourth power of the wavelength toward the red. This scattering of blue out of the sunlight leaves the "red-heavy" portion of the spectrum to be seen at sunset after the light has made the long trip through the atmosphere at low elevations.
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Mon Jun 26, 2023 7:51 pm
by orin stepanek
Wow; A lot of great photos in today's APOD
Kitty and doggy playing!
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Tue Jun 27, 2023 3:42 am
by Ann
orin stepanek wrote: ↑Mon Jun 26, 2023 7:51 pm
Wow; A lot of great photos in today's APOD
Orin, that's a great image!
I couldn't find it in the links of today's caption. Where did you find it?
Anyway, Victor, I very much recommend the image posted by Orin, because it does a great job of explaining the Belt of Venus!
Or at least I think so.
Don't miss the Earth's shadow on the Moon!
Ann
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Tue Jun 27, 2023 4:39 am
by bystander
Ann wrote: ↑Tue Jun 27, 2023 3:42 am
orin stepanek wrote: ↑Mon Jun 26, 2023 7:51 pm
Wow; A lot of great photos in today's APOD
Orin, that's a great image!
I couldn't find it in the links of today's caption. Where did you find it?
APOD: Shadows of Earth (2023 May 09)
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Tue Jun 27, 2023 4:43 am
by Ann
Thanks, bystander. I missed it.
Ann
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Tue Jun 27, 2023 12:12 pm
by VictorBorun
Ann wrote: ↑Tue Jun 27, 2023 3:42 am
orin stepanek wrote: ↑Mon Jun 26, 2023 7:51 pm
Wow; A lot of great photos in today's APOD
Orin, that's a great image!
I couldn't find it in the links of today's caption. Where did you find it?
Anyway, Victor, I very much recommend the image posted by Orin, because it does a great job of explaining the Belt of Venus!
Or at least I think so.
Don't miss the Earth's shadow on the Moon!
Ann
I think the full moon (and a partial eclipse) is a feature of the direction opposite to the low sun disk, the same direction as in the APOD discussed here.
So I just stay my ground and illustrate it with colour picker from San Diego sunset you showed above
...
Re: APOD: The Belt of Venus over Mount Everest (2023 Jun 26)
Posted: Tue Jun 27, 2023 3:05 pm
by orin stepanek
Ann wrote: ↑Tue Jun 27, 2023 3:42 am
orin stepanek wrote: ↑Mon Jun 26, 2023 7:51 pm
Wow; A lot of great photos in today's APOD
Orin, that's a great image!
I couldn't find it in the links of today's caption. Where did you find it?
Anyway, Victor, I very much recommend the image posted by Orin, because it does a great job of explaining the Belt of Venus!
Or at least I think so.
Don't miss the Earth's shadow on the Moon!
Ann
Thanks Ann; bystander got it for me!
Thanks bystander!