re: Analemma intersection

2018-04-15 Thread Robert Kellogg

Dan, Steve

Regarding the exact time of intersection: It requires a rather 
interesting problem of simultaneously minimizing EOT and declination 
between spring and fall dates.  Fortunately I have a spread sheet that 
implements the calculation of EOT to within a second or so and likewise 
precise declination.  I set up the difference of EOT(spring) - EOT(fall) 
and DEC(spring)-DEC(fall) as a pair of 2D tables using date/time 
variables.  To see small changes, I multiplied the DEC error in degrees 
by x100 and looked at EOT error in seconds.


For this year, the result to the nearest hour is 11 April, 7:00 UTC and 
28 Aug, 17:00 UTC corresponding to Julian Dates of

2458219.79167 and 2458359.20833.

Regards,
Bob
---
https://lists.uni-koeln.de/mailman/listinfo/sundial



Re: Analemma intersection

2018-04-13 Thread Ale de la Puente
Hello all,
I subscribe to this Sundial List because I am working on an art project
installation of a Sundial and a "Full Moondial" (however weird this
sounds).
I am an artist working on time, space and coincidences. I am writing you
now because of this last question and answers entries.
I find them inspiring and heartwarming.
Usually, I know no answer to all entries, I just learn from you all.
But today I can answer the question of Dan: *Does it have any special
significance? *
Yes, it does, since it arises the doubt of its significance.
It definitely makes me start a new art project about it.
Thank you Dan, and thank you all for this Sundial List. I will share with
you my results.
All the best and warm regards,
Ale



On Thu, Apr 12, 2018 at 6:55 PM, Roger W. Sinnott <roger.sinn...@verizon.net
> wrote:

> Roger (and others),
>
>
>
> A slight correction concerning the motion of Earth's perihelion with
> respect to the seasons. Owing to precession, the equinoxes and solstices
> drift slowly westward along the ecliptic in a cycle of about 26,000 years.
> But at the same time perturbations by the other planets cause the Earth's
> perihelion point to drift slowly eastward along the ecliptic.  The net
> effect is that the perihelion migrates all the way around the ecliptic
> (with respect to the seasons) in about 21,000 years.
>
>
>
> Bernard M. Oliver wrote a classic article about the changing shape of the
> analemma for Sky & Telescope (July 1972, pages 20-22). He gave A.D. 1246 as
> the year when perihelion and the winter solstice coincided.  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.
>
>
>
> (Full disclosure: I remember that article well, because one of its
> diagrams was the very first one I prepared after joining the magazine
> staff!)
>
>
>
> Roger S.
>
>
>
>
>
> *From:* sundial [mailto:sundial-boun...@uni-koeln.de] *On Behalf Of *Roger
> Bailey
> *Sent:* Thursday, April 12, 2018 6:13 PM
> *To:* Dan-George Uza; Sundial List
> *Subject:* 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
>
> Walking Shadow Designs
>
>
>
> *From:* Dan-George Uza <cerculdest...@gmail.com>
>
> *Sent:* Thursday, April 12, 2018 3:46 AM
>
> *To:* Sundial List <sundial@uni-koeln.de>
>
> *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
> --
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
> --
>
> [image: Image removed by sender. Avast logo]
> <https://www.avast.com/antivirus>
>
> This email has been checked for viruses by Avast antivirus software.
> www.avast.com <https://www.avast.com/antivirus>
>
>
>
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
>


-- 
...
*Ale de la Puente*

www.aledelapuente.org

skype: aledelapuente
T:  + 52 55 55 54 0895
M:  + 52 1 55 54 34 8548
Twitter: @aledelapuente
instagram @aledelapuente
---
https://lists.uni-koeln.de/mailman/listinfo/sundial



RE: Analemma intersection

2018-04-12 Thread Roger W. Sinnott
Roger (and others),

 

A slight correction concerning the motion of Earth's perihelion with respect to 
the seasons. Owing to precession, the equinoxes and solstices drift slowly 
westward along the ecliptic in a cycle of about 26,000 years. But at the same 
time perturbations by the other planets cause the Earth's perihelion point to 
drift slowly eastward along the ecliptic.  The net effect is that the 
perihelion migrates all the way around the ecliptic (with respect to the 
seasons) in about 21,000 years.

 

Bernard M. Oliver wrote a classic article about the changing shape of the 
analemma for Sky & Telescope (July 1972, pages 20-22). He gave A.D. 1246 as the 
year when perihelion and the winter solstice coincided.  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.

 

(Full disclosure: I remember that article well, because one of its diagrams was 
the very first one I prepared after joining the magazine staff!)

 

Roger S.

 

 

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Roger Bailey
Sent: Thursday, April 12, 2018 6:13 PM
To: Dan-George Uza; Sundial List
Subject: 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

Walking Shadow Designs

 

From: Dan-George Uza <mailto:cerculdest...@gmail.com>  

Sent: Thursday, April 12, 2018 3:46 AM

To: Sundial List <mailto:sundial@uni-koeln.de>  

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 

  _  

---
https://lists.uni-koeln.de/mailman/listinfo/sundial

 

  _  


 <https://www.avast.com/antivirus> Image removed by sender. Avast logo

This email has been checked for viruses by Avast antivirus software. 
www.avast.com <https://www.avast.com/antivirus>  





---
https://lists.uni-koeln.de/mailman/listinfo/sundial



Re: Analemma intersection

2018-04-12 Thread Roger Bailey
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
Walking Shadow Designs


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





---
https://lists.uni-koeln.de/mailman/listinfo/sundial



---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
---
https://lists.uni-koeln.de/mailman/listinfo/sundial