<p>Actually, the intersection point DOES have significance.</p>
<p>This is according to Roger Bailey and Dan-George Uza.</p>
<p>Where the intersection occurs is a result of the asymmetry of the analemma caused by the difference between the solstice date and perihelion dates.</p>
<p>Right now, those dates are different by about 12 days. But those dates are always shifting (albeit slowly).</p>
<p>That’s because of precession and the perturbation of other planets. The net effect is that the perihelion migrates all the way around the ecliptic (with respect to the seasons) every 21,000 years.</p>
<p>So when last did the perihelion happen exactly on the winter solstice? When was it 0 days difference instead of 12 days?</p>
<p>Well, the date drifts in a cycle of 21,000 years. So 12 days gives 12/365.25x21000 or 690 years ago: that would by 1334 A.D. … and the loops of the analemma would have been SYMMETRICAL on that date!</p>
<p>-Kurt Stammberger</p>
<p>P.S.
Actually the date is 1246 AD because of other details of the calculation, performed by Bernard M. Oliver. He wrote an important article about the changing shape of the analemma for Sky &amp; Telescope (July 1972, pages 20-22). Among the other
effects he noted, in A.D. 6489 the two lobes of the analemma will be essentially equal in size and perihelion will coincide with the vernal equinox.</p>

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2024-09-15T15:34:27.103Z
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2024-09-15T14:06:26.003Z
Kurt Stammberger
<p>The intersection corresponds to mid April and late August, the exact date will depend on where we are in the leap year cycle.</p>
<p>Sadly, there's no interesting link between a point in Earth's orbit, nor seasons, and this intersection point.</p>
<p>The analemma can be broken into two parts, the North-South movement, and the East-West movement.  The NS movement is due to the change in the declination of the Sun's <a href="https://www.celestialprogramming.com/snippets/geographicPosition.html" rel="noreferrer">Geographic Position</a>.  And the East-West movement is caused by the <a href="https://en.wikipedia.org/wiki/Equation_of_time" rel="noreferrer">Equation of Time</a>.  And, in fact, a plot of the equation of time vs declination produce the analemma:
<a href="https://i.sstatic.net/TPVon.png" rel="noreferrer"><img src="https://i.sstatic.net/TPVon.png" alt="enter image description here" /></a></p>
<p>The intersection isn't where either is a specific value, it's just where the two functions happen to have values the same as they had at some other point in the year.  They're not equal to each other, not zero, not the start of a season, not half way between seasons, nothing really interesting.</p>
<p>Both functions are a combined function of the Earth's axial tilt, and the Earth's orbit.  Plotted above, the EoT is the X coordinate, and the declination the Y coordinate.</p>
<p>An in depth exploration is <a href="https://mtirado.com/blog/demystifying-the-analemma/" rel="noreferrer">Demystifying the Analemma</a>, and the <a href="https://mtirado.com/resources/analemma-calc/index.html" rel="noreferrer">Analemma Calculator</a> allows you to explore how changing the Earth's orbit and axial tilt change the shape of the analemma.</p>

CC BY-SA 4.0
2022-11-23T18:18:33.850Z
2022-11-23T18:18:33.850Z
Greg Miller
<p>Is there an orbital significance to where the analemma intersects? Where in the earth's orbit does the intersection occur? I know the general dates when this happens but would like to know if it occurs at a significant position like the perihelion or aphelion.</p>

<analemma>
What is the significance of the intersection in the analemma?
Michael Hong
# What is the significance of the intersection in the analemma?

(Asked by: username_0 on 2022-11-23)

Is there an orbital significance to where the analemma intersects? Where in the earth's orbit does the intersection occur? I know the general dates when this happens but would like to know if it occurs at a significant position like the perihelion or aphelion.

**Tags:** analemma

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## 2 answers

### Answer by username_3 on 2022-11-23. Score: 12 | Accepted answer

The intersection corresponds to mid April and late August, the exact date will depend on where we are in the leap year cycle.

Sadly, there's no interesting link between a point in Earth's orbit, nor seasons, and this intersection point.

The analemma can be broken into two parts, the North-South movement, and the East-West movement. The NS movement is due to the change in the declination of the Sun's [Geographic Position](https://www.celestialprogramming.com/snippets/geographicPosition.html). And the East-West movement is caused by the [Equation of Time](https://en.wikipedia.org/wiki/Equation_of_time). And, in fact, a plot of the equation of time vs declination produce the analemma:
[![enter image description here](https://i.sstatic.net/TPVon.png)](https://i.sstatic.net/TPVon.png)

The intersection isn't where either is a specific value, it's just where the two functions happen to have values the same as they had at some other point in the year. They're not equal to each other, not zero, not the start of a season, not half way between seasons, nothing really interesting.

Both functions are a combined function of the Earth's axial tilt, and the Earth's orbit. Plotted above, the EoT is the X coordinate, and the declination the Y coordinate.

An in depth exploration is [Demystifying the Analemma](https://mtirado.com/blog/demystifying-the-analemma/), and the [Analemma Calculator](https://mtirado.com/resources/analemma-calc/index.html) allows you to explore how changing the Earth's orbit and axial tilt change the shape of the analemma.


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### Answer by username_1 on 2024-09-15. Score: 1

Actually, the intersection point DOES have significance.

This is according to Roger Bailey and Dan-George Uza.

Where the intersection occurs is a result of the asymmetry of the analemma caused by the difference between the solstice date and perihelion dates.

Right now, those dates are different by about 12 days. But those dates are always shifting (albeit slowly).

That’s because of precession and the perturbation of other planets. The net effect is that the perihelion migrates all the way around the ecliptic (with respect to the seasons) every 21,000 years.

So when last did the perihelion happen exactly on the winter solstice? When was it 0 days difference instead of 12 days?

Well, the date drifts in a cycle of 21,000 years. So 12 days gives 12/365.25x21000 or 690 years ago: that would by 1334 A.D. … and the loops of the analemma would have been SYMMETRICAL on that date!

-Kurt Stammberger

P.S.
Actually the date is 1246 AD because of other details of the calculation, performed by Bernard M. Oliver. He wrote an important article about the changing shape of the analemma for Sky & Telescope (July 1972, pages 20-22). Among the other
effects he noted, in A.D. 6489 the two lobes of the analemma will be essentially equal in size and perihelion will coincide with the vernal equinox.

> **Comments:**
> **username_2**: You may enjoy my https://astronomy.stackexchange.com/a/49605/16685  

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