# Re: Analemma intersection

```Hi Dan,
To me the value of the EQT at the intersection is an indication of the
asymmetry of the analemma caused by the difference between the solstice and
perihelion dates. The tilt of the earths axis is one parameter that defines the
analemma. This is shown at the extremes, the summer and winter solstices. The
eccentricity of the orbit is the other parameter that defines the analemma.
This is indicated by the perihelion. If the date of the perihelion is the same
as the solstice, I would expect the curve would be symmetrical and the EQT at
the intersection would be equal to zero. Perihelion was 2 Jan 2018 and the
winter solstice was 21 Dec 2018. This 12 day difference defines the offset of
the intersection of the analemma loops. When was the perihelion on the winter
solstice? The perihelion changes in a cycle of 25,800 years. So 12 days gives
12/365.25x25,800 or 878 years ago. In 1140 AD I would expect a symmetrical
analemma.```
```
Of course there is more to this than this simple approximation of orbital
dynamics. What was the actual date when the perihelion and solstice were the
same? I offer this as quick answer to the question on the significance of the
analemma curve intersection.

Regards, Roger Bailey

From: Dan-George Uza
Sent: Thursday, April 12, 2018 3:46 AM
To: Sundial List
Subject: Analemma intersection

Hello,

Tomorrow the Sun will have reached the point of intersection in the analemma
8-curve. How do you compute the exact time of intersection (i.e. when both the
hour angle and the solar declination match for two days)? And does it have any
special significance?

Dan

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