Correct me on something about the sun's movement in the sky

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Discussion Overview

The discussion revolves around the movement of the sun in the sky, particularly around the winter solstice, exploring its apparent motion from different frames of reference. Participants examine the sinusoidal nature of the sun's trajectory, mathematical descriptions of its movement, and the implications of Earth's motion on perceived solar movement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that around December 22nd, the sun appears to stop moving south for three days before moving upwards, while others frame this in terms of the sun's motion relative to Earth.
  • A mathematical expression for the rate of change of the sun's zenith angle is proposed, indicating that the highest daily rate of change occurs at the equinoxes.
  • Participants discuss the sinusoidal nature of the sun's motion, noting that it appears to hover briefly at solstices before reversing direction.
  • One participant mentions the term "analemma" as a way to describe the sun's figure 8 path in the sky.
  • There is a perspective that the sun's apparent movement is primarily due to Earth's motion, suggesting a non-Terracentric viewpoint.
  • Several participants inquire about the mathematical expression for the sun's movement, referencing plots of sun height and azimuth but expressing difficulty in finding a specific equation.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the sun's movement, with some emphasizing the sun's apparent motion due to Earth's rotation and orbit, while others focus on the sun's actual path. The discussion remains unresolved regarding the mathematical expressions and interpretations of solar movement.

Contextual Notes

Some mathematical steps and assumptions regarding the sun's motion and the frame of reference are not fully resolved, and the discussion includes varying interpretations of the sun's trajectory.

Mk
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By December 22nd the sun seems to stop moving south and rests for three days, until December 25th when it moves approximately one degree upwards
Would this statement be correct?
 
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Mk said:
By December 22nd the sun stops moving south and rests for three days, until December 25th when it moves approximately one degree upwards
Exactly correct from a frame of reference that by December 22nd stops moving north and rests for three days, until December 25th when it moves approximately one degree downwards with respect to the sun.
 
d(phizenith)/dt ~ 23 ( 2pi/365.25 ) sin ( t 2pi/365.25 ) , where t = days since solstice, or t0 = solstice dates. Highest daily rate of change of zenith angle (elevation) is 1/3 degree per day, and occurs at the vernal and autumnal equinoxes.
 
As Bystander is trying to say. The Suns motion is sinusoidal, at the solstice it reaches its extreme position for the season. The rate of change is very small at these times (Summer and Winter) So the sun appears to hover briefly as it changes direction. It is not really stationary it is just moving very slowly. It then begins to accelerate, slowly initially, then as it speeds up, reaches the maximum rate of change at the Equinox. At this time the sun races past the equator but even then the rate of change begins to drop as the sun moves toward the other extreme.
 
Thanks for all three of the replies, I figured it would be sinusoidal motion, and it just slowerly and slowerly moved, until it reversed it's path of acceleration. Thanks for the math, Bystander.
 
Look up "analemma". That is the name of the sun's figure 8 path against the sky.
 
Maybe it's just because I was born a non-Terracentric, but I prefer to think that the sun just pretty much stays the same and the motion of the Earth makes it appear to move.
 
Danger said:
Maybe it's just because I was born a non-Terracentric, but I prefer to think that the sun just pretty much stays the same and the motion of the Earth makes it appear to move.
Heretic! :mad:

:-p
 
Hello to all!
I don't know if anyone will check this but...here is my question:

what is the sun time equation that describes sun's movement ?
I have found plots of sun's height (in degrees) (vertical axes height-horizontal sun azimuth in degrees) but I can't find it's mathematical expression...
 
  • #10
Read post #6.
 
  • #11
mplak said:
Hello to all!
I don't know if anyone will check this but...here is my question:

what is the sun time equation that describes sun's movement ?
I have found plots of sun's height (in degrees) (vertical axes height-horizontal sun azimuth in degrees) but I can't find it's mathematical expression...

http://www.analemma.com/Pages/framesPage.html

http://en.wikipedia.org/wiki/Equation_of_time
 
  • #12
Danger said:
Maybe it's just because I was born a non-Terracentric, but I prefer to think that the sun just pretty much stays the same and the motion of the Earth makes it appear to move.


I was just about to say the same thing.

Thank you.
 
  • #13
Equate said:
I was just about to say the same thing.

Thank you.

He's kidding.

This thread is not about what we think; it is about what we observe. We observe the movement of the sun from our rest frame.
 
  • #14
Thought so.

It's a big conspiracy. I could have sworn I saw the far side of the moon the other day, but no one believed me.

Oh well...
 

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