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Polar evening



 
 
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  #1  
Old February 18th 18, 10:09 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Polar evening

https://www.usap.gov/videoclipsandmaps/spwebcam.cfm

In about a month, the forward motion of the Earth through space will turn the South pole through the planet's circle of illumination for the one and only time in 2018 at Polar sunset.

https://epic.gsfc.nasa.gov/

I assume that although it makes so much sense to treat the planet's two distinct day/night cycles separately via distinct rotational causes, the allegiance to celestial sphere reckoning is so entrenched that people would rather ignore what is correct for nothing more than convenience purposes.

  #2  
Old February 18th 18, 07:49 PM posted to sci.astro.amateur
Quadibloc
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Default Polar evening

On Sunday, February 18, 2018 at 2:09:45 AM UTC-7, Gerald Kelleher wrote:

I assume that although it makes so much sense to treat the planet's two distinct
day/night cycles separately via distinct rotational causes, the allegiance to
celestial sphere reckoning is so entrenched that people would rather ignore what
is correct for nothing more than convenience purposes.


What is correct is that the annual cycle seen in isolation at the poles is caused
by the revolution of the planet around the Sun, not by any form of rotation.

John Savard
  #3  
Old February 18th 18, 08:09 PM posted to sci.astro.amateur
Gerald Kelleher
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Default Polar evening

Rotation as a function of the orbital motion of the Earth turns the North and South poles parallel to the orbital plane. Easy enough to discern via the Antarctic Continent from September to March representing the day part of the polar day/night cycle -

https://www.youtube.com/watch?v=CFrP6QfbC2g&t=92s

Genuine teachers would have no difficulty with the principle that in the absence of daily rotation, the entire surface of the planets turns once each year to the Sun as a function of the forward orbital motion of the Earth through space.

  #4  
Old February 24th 18, 11:58 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Polar evening

https://epic.gsfc.nasa.gov/?date=2017-12-21

https://epic.gsfc.nasa.gov/?date=2018-02-22

The comparisons on the December Solstice with today are as striking for the intentional avoidance of the cause of the difference than for the imaging itself. I genuinely appreciate the NASA team for placing a satellite that picks up the fully illuminated side of the Earth ( ultimately have a full array of satellites from the two other half illuminated points).

Instead of a literal pole sticking out of the Earth, why not operate with the single surface rotation where the surface turns parallel to the ecliptic as a function of the orbital motion of the Earth. Nobody is going to complain or short about priority but so long as it is done.
  #5  
Old February 28th 18, 09:28 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Polar evening

In 20 days the North and South poles turn through the circle of illumination thereby dividing the day part from the night part of the polar cycle for each respective polar location. The revised values given for the relationship between the polar points and the circle of illumination are based on the distance the North/South poles turn across the fully illuminated face of the planet. In much the same way all locations turn through a distance when it exits the circle of illumination (sunrise) to re-entering it (sunset) as a function of daily rotation, the orbital surface rotation can be treated in much the same way although just as interesting for the differences involved in variable orbital speed.

The entire surface of the Earth turns, on average, about 60.97 miles per day and parallel to the ecliptic as a function of the planet's orbital motion so currently the polar points are roughly 1,219 miles from the circle of illumination. The day part of the cycle in the Southern hemisphere is coming to an end while the Northern hemisphere the day part is about to begin as polar dawn is now well established in the Northern polar latitude.

What can be said for a community who vacillate between a tilting Earth and a pivoting circle of illumination but that is altogether a different story.


 




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