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Science of the Equinox



 
 
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  #1  
Old September 16th 17, 07:18 PM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

A person at the Equator experiences a symmetry of daylight/darkness throughout an orbit of the Sun while their counterpart at the South pole also experiences the same symmetry with a notable difference.

Where the dawn/twilight periods are almost negligible at the Equator compared to other latitudes as a function of daily rotation, the extended dawn/twilight periods as a function of the orbital surface rotation highlight the need to partition the planet's dual day/night cycles by cause.

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

Because there is no seasonal asymmetry in daylight/darkness at the Equator, the preposterous RA/Dec idea of the Sun crossing an imaginary celestial equator on the Equinox is disruptive for those who wish to enjoy the science behind this semi-annual event.

On the day of the Equinox in a few days time, the person at the Equator shares a sunrise with the person at the South pole but arising from separate causes as once the Sun comes into view at the polar latitude it stays in view for 6 months. I wish people to row in behind this approach and inform those who have a public responsibility for education to adjust their views accordingly.
  #2  
Old September 17th 17, 10:41 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

Despite the amazing freezing temperatures at the South pole presently, the imaging of polar dawn,soon to be replaced by polar sunrise, are quite lovely -

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

It would normally be an occasion to appreciate planetary temperatures and how they fluctuate North to South as each hemisphere, in turn, receives more radiation than the other.
  #3  
Old September 18th 17, 11:06 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

With the rise of celestial sphere software based on RA/Dec,the descriptions have followed suit using this framework and the changes occurred even in the period that this newsgroup has been in operation. The emergence of the internet along with computer software has influenced descriptions in such a way that even the 'tilting' Earth has given way to an idea that the Sun moves up and down against a median line called the celestial Equator -

http://www.nakedeyeplanets.com/const...c-labelled.png

The Equinox is a unique astronomical event in the daily and annual cycle of the Earth, the day of two distinct types of sunrises where the Sun comes into view due to two distinct motions.




  #4  
Old September 19th 17, 03:37 PM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

What a wonderful image of the first light of the Sun in the telescope camera -

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

The symphony of motions is delightful as polar dawn breaks when the Sun comes into full view in a few days.
  #5  
Old September 20th 17, 09:03 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

To those who state that posting within the same threads multiples time without responses in counter-productive, it spares readers from seeing multiple individual threads. That being said there are no accurate descriptions of the Equinox out there showing the difference between the Equator and the North/South poles in terms of sunrise/sunset.

https://www.timeanddate.com/astronom...-guinea/malabo

Apart from the small variation supplied by the variable surface rotation speed as a function of orbital motion, sunrise/sunset at the Equator is more or less symmetrical whereas at the North and South poles the orbital surface rotation takes over and there is just a single sunrise and sunset for each orbit of the Sun.

It should be prevent those from describing the Sun 'directly over the Equator' on the equinox or an imagined motion South of the Equator but presently it doesn't even though there is nothing to be gained by that celestial sphere perspective.

  #6  
Old September 21st 17, 09:05 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

There are precious few external references for determining the fractional proportion of rotations to one orbital circuit apart from the noble original reference taken across 4 annual circuits of the Earth around the Sun. Taken from any date, the first appearance of Sirius or indeed any major star will take 365 days/rotations for three circuits but on the fourth circuit of 365 days the star will not appear but be delayed by one day/rotation. The calendar framework is based on this principle however the natural reference for one circuit does not exist by this method so it is by a process of deduction that 1461 days/rotations correspond to 4 annual circuits then 365 1/4 days/rotations correspond to one circuit.

The Equinox provides a new reference insofar as from polar sunrise to sunset or its obverse, 182.62 days/rotations will have passed, of course this is a rough value corresponding to 365.25 days that make up the calendar system without the other adjustments. From the first moment the Sun appears tomorrow at the South pole until its exit on the March 2018 equinox, there is an opportunity, weather permitting, to gauge the proportion for the first time in human history and work out the details later.
  #7  
Old September 22nd 17, 10:29 AM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

We have two different types of sunsets in our hemisphere today, the normal sunset which happens at 7:23 PM for Dublin and the Northern polar sunset at 9:02 PM (as an event within the polar day/night cycle) where the Sun goes out of view for 6 months at the North pole until the March Equinox when it returns. At the same time the Sun will come into view at the South pole today (polar sunrise) for the Southern hemisphere and with good weather conditions presently at the Pole ,that sunrise should be visible today -

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

Of course the time of local daily sunset coinciding with the polar sunset changes depending on the longitude of the observer nevertheless it is there whether one person appreciates it or nobody else.
  #8  
Old September 22nd 17, 03:55 PM posted to sci.astro.amateur
Gerald Kelleher
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Default Science of the Equinox

Northern polar sunset happens at 9:20 GMT of about 2 hours after local sunset in Dublin and happens about 2 hours before sunset in Washington where daily sunset happens at 7:05 PM.

People should enjoy polar sunrise even if it is just gone out of frame -

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




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