Why Does the Analemma Show an Ellipse for Solstices?

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Discussion Overview

The discussion revolves around the representation of solstices on an analemma, specifically why solstices are depicted as an ellipse rather than a single point. Participants explore the implications of the timing of solstices and the nature of solar declination throughout the year.

Discussion Character

  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant notes that the analemma shows 365 marks for each day of the year, with solstices represented by an ellipse due to their varying occurrence dates (20, 21, or 22 June/December) and the low declination speed near solstices.
  • Another participant asserts that an analemma is inherently an ellipse, suggesting that the figure 8 shape represents the Sun's movement throughout the year.
  • A later reply clarifies that the solstices are not marked by a single point but rather by an ellipse, questioning the reason for this representation.
  • Some participants express confusion about the ellipse's representation, with one reiterating that the analemma forms a figure 8 and questioning the existence of an ellipse in this context.
  • One participant suggests that the ellipse may serve as an "envelope" for the different possible positions of the Sun during solstices, given the variations in timing and the close proximity of solar positions near these dates.
  • Another participant inquires whether the discussion pertains to a single year or multiple years, indicating a potential distinction in the interpretation of the analemma.
  • A response indicates that the analemma in question is a permanent one, suggesting it is intended to represent multiple years.

Areas of Agreement / Disagreement

Participants express varying interpretations of the analemma and its representation of solstices. There is no consensus on the exact reason for the elliptical representation, and confusion remains regarding the terminology and concepts involved.

Contextual Notes

The discussion includes assumptions about the nature of the analemma and the timing of solstices, which may not be universally understood. The dependence on definitions of terms like "ellipse" and "analemma" may affect clarity.

JeffOCA
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Hi,

In a regular analemma, you have 365 marks on the ground where the sunlight fall every day at true solar noon. The equinoxes and solstices are also represented on the analemma.

To indicate the solstices, you don't have a point on the ground but a kind of ellipse. I think this is due to solstices that don't strictly occur the same day (20, 21 or 22 june / december) and also because near solstices the declination speed is very low, so the positions are too close to be represented individually, so an ellipse as an envelope of the different possible positions.

Can you confirm or infirm ?

Thanks
 
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What do you mean by a "regular analemma"?

As far as I know, an analemma IS an ellipse. If you mark a spot each week or day for an entire year and then connect the dots you will make a figure 8 ellipse that shows the movement of the Sun in the sky for that year.

http://en.wikipedia.org/wiki/Analemma
 
I know analemma makes a figure 8 slightly deformed. The word "regular" wasn't appropriate, forget it !
My question was (sorry if it was not clear enough) : each mark on the ground is a point for each day of the year but to mark the solstices we have a kind of ellipse containing several points. Why we have such an ellipse to mark solstices ?

I hope it's more clear now.

Thanks
 
Anyone ?
 
I have no idea what you are talking about. What ellipse are you referring to? The analemma makes a figure 8, so I don't see any ellipses other than the two ellipses that form the figure 8.
 
Drakkith said:
I have no idea what you are talking about. What ellipse are you referring to? The analemma makes a figure 8, so I don't see any ellipses other than the two ellipses that form the figure 8.

Sorry for the misunderstanding, but english is not my mother tongue. I agree analemma makes a figuer 8. On this figure 8, you have on the floor 365 marks for the 365 days of the year. You have also other indications like months, equinoxes, solstices, etc.
But, on the figure 8, the position of the solstice is not marked by a single dot but with a little ellipse (in dotted line). Why ?

My first ideas were :
- Solstice doesn't strictly occur at the same day (20, 21 or 22 june / december) for a given year.
- in addition, near solstices the sun declination speed is very low, so the positions of the sunspot on the ground are too close day by day to be represented individually, as singles positions. So we draw an ellipse which the "envelope" of the different possible positions for solstice.

I hope that my words are clearer now...

Thanks
 
Are you talking about an analemma for a single year, or multiple years?
 
Drakkith said:
Are you talking about an analemma for a single year, or multiple years?

This analemma (where I see an ellipse for delimiting the solstice) is engraved in the ground, so i think it is an permanent analemma, for multiple years...
 
JeffOCA said:
This analemma (where I see an ellipse for delimiting the solstice) is engraved in the ground, so i think it is an permanent analemma, for multiple years...

I'm not sure, but I think your reasoning is correct in this case. Since the solstice occurs at different times each year it would not be a single spot.
 

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