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The long shadows



 
 
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  #1  
Old March 15th 19, 07:07 PM posted to sci.astro.amateur
Gerald Kelleher
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Default The long shadows

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

In a number of days, the Sun will disappear from view for 6 months in what is one of the great astronomical events - two distinct types of sunrise and sunset within the same 24 hour day.

https://www.timeanddate.com/sun/antarctica/south-pole

With children taking to the streets for the sake of experimentalists, it is a pity they never learn about the good things in astronomy and its creative/productive centre.
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  #2  
Old March 16th 19, 10:43 PM posted to sci.astro.amateur
Quadibloc
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Default The long shadows

On Friday, March 15, 2019 at 1:07:36 PM UTC-6, Gerald Kelleher wrote:

In a number of days, the Sun will disappear from view for 6 months


Of course, this applies to the immediate vicinity of the South Pole, as your link
makes apparent.

in what is one of the great astronomical events - two distinct types of sunrise
and sunset within the same 24 hour day.


And these two distinct types of sunrise and sunset are consequences of the Earth
having two distinct rotational motions. One being "orbital rotation", the other
being "daily rotation" as I think you call them.

Now, then, as I am sure you are aware, the Earth is a rigid body. This means
that these two types of rotation are inseparable, and every part of the Earth
experiences both of them.

This means that since "orbital rotation" has a period of one year, in order for
people at temperate and tropical latitudes to experience a 24 hour day, "daily
rotation" must have a period differing from 24 hours, in order that the _sum_ of
daily rotation and orbital rotation will yield a 24 hour day.

So "daily rotation" must have a period of 23 hours, 56 minutes, and 4 seconds,
or thereabouts.

John Savard
  #3  
Old March 17th 19, 10:23 PM posted to sci.astro.amateur
Gerald Kelleher
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Default The long shadows

There are a number of helpful approaches that makes it easier for people to arrive at the surface rotation as a function of the orbital motion of the Earth.

A more productive approach is that one hemisphere of the Earth constantly faces the same direction in space so that it must turn to the Sun as a consequence of this orbital motion, this face is demarcated by the circle of illumination. In this respect, it is easier to drop the broom analogy and walk around an object representing the Sun so that all sides of the body face the object/Sun during an orbital circuit. It really doesn't need further qualification but opens up a whole new set of principles which incorporate compound motions - the planets around the Sun and the planets and the Sun moving in one direction in space.

I regret there really isn't a platform to expand on this approach rather than pointing out deficiencies in existing academic structures but I am hopeful it will eventually surface in more responsible circles.
 




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