APOD: Eclipse on a Polar Day (2021 Dec 10)

Comments and questions about the APOD on the main view screen.
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APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by APOD Robot » Fri Dec 10, 2021 5:05 am

Image Eclipse on a Polar Day

Explanation: During polar day, in Arctic and Antarctic summer, the Sun stays above the horizon for periods of 24 hours or more. Recorded on December 4, this fisheye timelapse image tracks the Sun in multiple frames as it completes a circle in the summer sky above Union Glacier, Antarctica. Of course on that date, Union Glacier's sky did grow dark even though the Sun was above the horizon. Captured during the brief period of totality, an eclipsed Sun is at bottom center of the composite view. Near the edge of the total eclipse path across planet Earth, the Moon's shadow darkens the sky above.

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RocketRon

Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by RocketRon » Fri Dec 10, 2021 5:10 am

What a brilliant set of photographs.
Thanks for posting/sharing.

And a strange concept for most Earthlings !?

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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by De58te » Fri Dec 10, 2021 8:49 am

Makes me wonder. Do fish's eyes really see the world like that? In a way it makes logical sense, since fish have things that want to eat them coming up from below as well as coming down from above!

Randall Rathbun

Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by Randall Rathbun » Fri Dec 10, 2021 10:34 am

What planet us that at the 4:30 position? Venus?

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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by orin stepanek » Fri Dec 10, 2021 1:07 pm

Eclipseclock-final2.JPG
Normally I don't care for fish-eye views; but I like this one! 8-)
midnight-sun.jpg
Nordkapp, Norway and midnight sun!
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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by neufer » Fri Dec 10, 2021 3:35 pm

De58te wrote: Fri Dec 10, 2021 8:49 am
Makes me wonder. Do fish's eyes really see the world like that?

In a way it makes logical sense, since fish have things that want to eat them coming up from below as well as coming down from above!
Click to play embedded YouTube video.
https://en.wikipedia.org/wiki/Fisheye_lens wrote:
<<The term fisheye was coined in 1906 by American physicist and inventor Robert W. Wood based on how a fish would see an ultrawide hemispherical view from beneath the water (a phenomenon known as Snell's window). Wood published a paper detailing an experiment in which he built a camera in a water-filled pail starting with a photographic plate at the bottom, a short focus lens with a pinhole diaphragm located approximately halfway up the pail, and a sheet of glass at the rim to suppress ripples in the water. The experiment was Wood's attempt "to ascertain how the external world appears to the fish" and hence the title of the paper was "Fish-Eye Views, and Vision under Water". Wood subsequently built an improved "horizontal" version of the camera omitting the lens, instead using a pinhole pierced in the side of a tank, which was filled with water and a photographic plate. In the text, he described a third "Fish-Eye" camera built using sheet brass, the primary advantages being that this one was more portable than the other two cameras, and was "absolutely leaktight". In his conclusion, Wood thought that "the device will photograph the entire sky [so] a sunshine recorder could be made on this principle, which would require no adjustment for latitude or month" but also wryly noted "the views used for the illustration of this paper savour somewhat of the 'freak' pictures of the magazines."

W.N. Bond described an improvement to Wood's apparatus in 1922 which replaced the tank of water with a simple hemispheric glass lens, making the camera significantly more portable. The focal length depended on the refractive index and radius of the hemispherical lens, and the maximum aperture was approximately f/50; it was not corrected for chromatic aberration and projected a curved field onto a flat plate. Bond noted the new lens could be used to record cloud cover or lightning strikes at a given location. Bond's hemispheric lens also reduced the need for a pinhole aperture to ensure sharp focus, so exposure times were also reduced.>>
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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by Eclectic Man » Fri Dec 10, 2021 3:53 pm

Randall Rathbun wrote: Fri Dec 10, 2021 10:34 am What planet us that at the 4:30 position? Venus?
As Venus, and all other astronomical objects, would have the same position relative to the sun in the frame, Venus should appear 24 times, like the sun. So it may be something more terrestrial, that was only visible once in the 'day' when the multiple images were taken.

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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by Chris Peterson » Fri Dec 10, 2021 4:11 pm

Randall Rathbun wrote: Fri Dec 10, 2021 10:34 am What planet us that at the 4:30 position? Venus?
It is possible, depending on how the image was constructed (for instance, when in the sequence the landscape image was collected). Its location with respect to the ecliptic is just about right. Venus was lagging the Sun by about 40°, with the images taken every 15° (you can see Venus over the hills in the linked video). Most of the possible images of Venus are likely to be hidden by the glare of the Sun in later images. If we could see the 24 individual frames unstacked, we'd likely see Venus in most or all of the images.
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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by neufer » Fri Dec 10, 2021 4:31 pm

Chris Peterson wrote: Fri Dec 10, 2021 4:11 pm
Randall Rathbun wrote: Fri Dec 10, 2021 10:34 am
What planet us that at the 4:30 position? Venus?
It is possible, depending on how the image was constructed (for instance, when in the sequence the landscape image was collected). Its location with respect to the ecliptic is just about right. Venus was lagging the Sun by about 40°, with the images taken every 15° (you can see Venus over the hills in the linked video). Most of the possible images of Venus are likely to be hidden by the glare of the Sun in later images. If we could see the 24 individual frames unstacked, we'd likely see Venus in most or all of the images.
We'd likely see Venus in most or all of the images with the Sun fully shining :?:
https://www.fourmilab.ch/cgi-bin/Yoursky wrote:

Code: Select all

[UT 7:34:38] From 76°48'S 46°12'W:
---------------------------------------
        Altitude   Azimuth
.......................................
Sun	17.246°	  −65.514°
Moon	18.217°	  −65.507°
Venus	12.226°	  −24.372°
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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by Chris Peterson » Fri Dec 10, 2021 6:08 pm

neufer wrote: Fri Dec 10, 2021 4:31 pm
Chris Peterson wrote: Fri Dec 10, 2021 4:11 pm
Randall Rathbun wrote: Fri Dec 10, 2021 10:34 am
What planet us that at the 4:30 position? Venus?
It is possible, depending on how the image was constructed (for instance, when in the sequence the landscape image was collected). Its location with respect to the ecliptic is just about right. Venus was lagging the Sun by about 40°, with the images taken every 15° (you can see Venus over the hills in the linked video). Most of the possible images of Venus are likely to be hidden by the glare of the Sun in later images. If we could see the 24 individual frames unstacked, we'd likely see Venus in most or all of the images.
We'd likely see Venus in most or all of the images with the Sun fully shining :?:
https://www.fourmilab.ch/cgi-bin/Yoursky wrote:

Code: Select all

[UT 7:34:38] From 76°48'S 46°12'W:
---------------------------------------
        Altitude   Azimuth
.......................................
Sun	17.246°	  −65.514°
Moon	18.217°	  −65.507°
Venus	12.226°	  −24.372°
Here is a stacked set of 24 hourly images (the eclipse happens in the SE). As you can see, Venus is very close to the Sun in every image.
_
Eclipse-Day-Sim.jpg
Here is an animation of the same data. The system seems to butcher animated GIFs when it shrinks them. Ignore that and just click on the image to get the full sized version, which seems to look fine in my browser.
_
Eclipse-Day-Sim.gif
I'd say the dot in the APOD could easily be Venus, captured when the landscape layer was obtained. No way to know for sure, though, without seeing the individual frames. I also note that the dot is in almost exactly the position of Venus during totality, and given that the totality frame was a longer exposure than the rest, it makes sense that's the one where Venus would be most apparent.
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neufer
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Re: APOD: Eclipse on a Polar Day (2021 Dec 10)

Post by neufer » Fri Dec 10, 2021 6:28 pm

Chris Peterson wrote: Fri Dec 10, 2021 6:08 pm
I'd say the dot in the APOD could easily be Venus, captured when the landscape layer was obtained. No way to know for sure, though, without seeing the individual frames. I also note that the dot is in almost exactly the position of Venus during totality, and given that the totality frame was a longer exposure than the rest, it makes sense that's the one where Venus would be most apparent.
I'd say the dot in the APOD is clearly Venus, captured when it was most visible (i.e., when the eclipse took place).
Art Neuendorffer