APOD: Traces of the Sun (2016 Dec 21)

Comments and questions about the APOD on the main view screen.
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APOD: Traces of the Sun (2016 Dec 21)

Post by APOD Robot » Wed Dec 21, 2016 5:09 am

Image Traces of the Sun

Explanation: This year the December Solstice is today, December 21, at 10:44 UT, the first day of winter in the north and summer in the south. To celebrate, watch this amazing timelapse video tracing the Sun's apparent movement over an entire year from Hungary. During the year, a fixed video camera captured an image every minute. In total, 116,000 exposures follow the Sun's position across the field of view, starting from the 2015 June 21 solstice through the 2016 June 20 solstice. The intervening 2015 December 22 solstice is at the bottom of the frame. The timelapse sequences constructed show the Sun's movement over one day to begin with, followed by traces of the Sun's position during the days of one year, solstice to solstice. Gaps in the daily curves are due to cloud cover. The video ends with stunning animation sequences of analemmas, those figure-8 curves you get by photographing the Sun at the same time each day throughout a year, stepping across planet Earth's sky.

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by JohnD » Wed Dec 21, 2016 9:39 am

A very pretty thing, that I enjoyed so much, when the usual analemma pictures are static and boring, that I went to find out more about this figure, and why it has two differently sized loops The Wiki article is especially confusing! https://en.wikipedia.org/wiki/Analemma
The paragraph "Solar analemma as seen from Earth" says that the smaller loop is on top from the Northern hemisphere, but below from the Southern. Is that true? I expected that there would be a smaller loop on top from either hemisphere, getting smaller as one approached the Poles and more equal as one approached the Equator, where the loops would be equal in size.

It's clear to me that the extreme of each loop marks the Solstice, but why are the Equinoxes not where the loops cross? That's in the analemma from the Royal Observatory, so I have to believe that!
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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by Boomer12k » Wed Dec 21, 2016 9:43 am

Awesome Presentation... thanks.

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by RedFishBlueFish » Wed Dec 21, 2016 11:01 am

Mesmerising and Memorable.

Köszönöm!


Though, as 2016 draws to a close, one cannot keep from recalling the words of Viscount Grey about a century ago: "The lamps are going out all over Europe, we shall not see them lit again in our life-time"

In this century, unlike the last, the light of democracy seems to be flickering in the United States of America as well.

Egy békés napforduló > A solstitiali pacis > Un solsticio apacible > A Peaceful Solstice

Joyeux Noël

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by BostonLarry » Wed Dec 21, 2016 11:28 am

Stunning not only technically, but conceptually. The parade of analemmas was brilliant! And as I am giving the final exam in my Solar System Astronomy class today, I'll have to rewrite a question to include this innovative display of a great data set.

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by hamilton1 » Wed Dec 21, 2016 11:54 am

RedFishBlueFish wrote:In this century, unlike the last, the light of democracy seems to be flickering in the United States of America as well.
The rejection of an establishment is actually proof of a strong democracy, unless you're opposed to change of course.

DanielP

Re: APOD: Traces of the Sun (2016 Dec 21)

Post by DanielP » Wed Dec 21, 2016 12:09 pm

Interesting and original sequences! One feature puzzles me, the interferences ovals visible at 0:25 and later when many daily tracks are superposed.
Are they coming from a front windows, or could result from interferences in the camera?

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by Guest 2 » Wed Dec 21, 2016 12:39 pm

Stunning not only technically, but conceptually. The parade of analemmas was brilliant! And as I am giving the final exam in my Solar System Astronomy class today, I'll have to rewrite a question to include this innovative display of a great data set.
This is little known but true nevertheless: Meteorology describes seasons as a 3 month period which always begins on the first of a month and which ends on the last day of the 3rd month. Thus seasons from the weatherman, while confusing are always defined exactly by duration's.Winter began Dec 1 and will be followed Spring on Mar 1. Having taught astronomy myself we should realize that there are both kinds seasons in the world.

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by ChrisKotsiopoulos » Wed Dec 21, 2016 12:54 pm

Amazing!
It's hard to imagine a better Solstice presentation!

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by ignacio_db » Wed Dec 21, 2016 2:41 pm

Loved the music too!

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by neufer » Wed Dec 21, 2016 3:55 pm

Click to play embedded YouTube video.
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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by NateWhilk » Wed Dec 21, 2016 5:14 pm

DanielP wrote:Interesting and original sequences! One feature puzzles me, the interferences ovals visible at 0:25 and later when many daily tracks are superposed.
Are they coming from a front windows, or could result from interferences in the camera?
I noticed them, too. Anyone know why they're there?

They also seem more pronounced in the summer to winter images.

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by alter-ego » Wed Dec 21, 2016 6:31 pm

JohnD wrote:A very pretty thing, that I enjoyed so much, when the usual analemma pictures are static and boring, that I went to find out more about this figure, and why it has two differently sized loops The Wiki article is especially confusing! https://en.wikipedia.org/wiki/Analemma
The paragraph "Solar analemma as seen from Earth" says that the smaller loop is on top from the Northern hemisphere, but below from the Southern. Is that true? I expected that there would be a smaller loop on top from either hemisphere, getting smaller as one approached the Poles and more equal as one approached the Equator, where the loops would be equal in size.

It's clear to me that the extreme of each loop marks the Solstice, but why are the Equinoxes not where the loops cross? That's in the analemma from the Royal Observatory, so I have to believe that!
John
So first, the analemma's shape is constant for all locations on earth, only the viewing perspective changes.
The small loop is always on the northern end of the analemma. The apparent flip between the northern and southern hemispheres is due to a 180° change in viewing direction. In the north one faces southward to view the analemma. In the south, one faces northward. In the northern hemisphere, if you face northward and lean backward you'll view the analemma with the big loop at the "top".

Second, the loops are different sizes due to earth's elliptical orbit.
Earth is closest to the sun during the northern winter months, so the apparent position of the sun is changing the fastest, thus how fast/slow the sun appears is greatest between these months. For a perfectly circular orbit, the analemma would be a symmetrical figure 8 with identical loops (the loops are due to the earth's tilted rotation axis, not ellipticity), and there would be equal times between the equinoxes and solstices, i.e. the crossing point would be the equinoxes. By definition, the equinoxes occur when the sun crosses the equator (0° declination). Because the orbit is elliptical, the crossing point actually occurs at ~9° declination. It doesn't take much ellipticity to dramatically change the analemma. In fact, both the analemma's slight east/west lean and loop asymmetry is entirely due to the orbital eccentricity.

Hope this helps.
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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by neufer » Wed Dec 21, 2016 7:03 pm

NateWhilk wrote:
DanielP wrote:
One feature puzzles me, the interferences ovals visible at 0:25 and later when many daily tracks are superposed.
Are they coming from a front windows, or could result from interferences in the camera?
I noticed them, too. Anyone know why they're there?

They also seem more pronounced in the summer to winter images.
https://en.wikipedia.org/wiki/Newton%27s_rings wrote:

<<Newton's rings is a phenomenon in which an interference pattern is created by the reflection of light between a spherical surface and an adjacent touching flat surface. Newton first studied the effect in 1717.

:arrow: Newton's rings seen in two plano-convex lenses with their flat surfaces in contact. One surface is slightly convex, creating the rings. In white light, the rings are rainbow-colored, because the different wavelengths of each color interfere at different locations.>>
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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by gak2000 » Wed Dec 21, 2016 8:39 pm

I am confused by the trajectories that the sun follows each day. In the summer, the sun is near the top of image at either edge and lower in the middle. In the winter, the trajectories curve the other way. Presumably the camera has a wide-angle lens that distorts the image. So, could someone explain the perspective in more detail (i.e. how the celestial sphere is mapped to this 2d image).

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by JohnD » Wed Dec 21, 2016 8:45 pm

Thank you, alter-ego!

Better understood now.
John

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by neufer » Wed Dec 21, 2016 9:15 pm

gak2000 wrote:
I am confused by the trajectories that the sun follows each day. In the summer, the sun is near the top of image at either edge and lower in the middle. In the winter, the trajectories curve the other way. Presumably the camera has a wide-angle lens that distorts the image. So, could someone explain the perspective in more detail (i.e. how the celestial sphere is mapped to this 2d image).
It appears to be an oblique stereographic projection centered
at the latitude and the opposing longitude of the observer.
https://en.wikipedia.org/wiki/Stereographic_projection wrote: <<The fundamental problem of cartography is that no map from the sphere to the plane can accurately represent both angles and areas. In general, area-preserving map projections are preferred for statistical applications, while angle-preserving (conformal) map projections are preferred for navigation.

Stereographic projection falls into the second category. When the projection is centered at the Earth's north or south pole, it has additional desirable properties: It sends meridians to rays emanating from the origin and parallels to circles centered at the origin. The stereographic is the only projection that maps all circles of a sphere to circles. This property is valuable in planetary mapping when craters are typical features. The set of circles passing through the point of projection have unbounded radius, and therefore degenerate into lines.>>
Last edited by neufer on Wed Dec 21, 2016 9:36 pm, edited 1 time in total.
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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by Randy Nagy » Wed Dec 21, 2016 9:31 pm

Awesome! Very similar to a lissajous pattern.

heehaw

Re: APOD: Traces of the Sun (2016 Dec 21)

Post by heehaw » Wed Dec 21, 2016 9:34 pm

If I had a daughter, I'd call her "Anna Lemma" now!

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by neufer » Wed Dec 21, 2016 9:48 pm

heehaw wrote:
If I had a daughter, I'd call her "Anna Lemma" now!
https://en.wikipedia.org/wiki/Finnegans_Wake#Anna_Livia_Plurabelle_.28ALP.29 wrote: <<Finnegans Wake is a work of comic fiction by Irish writer James Joyce. Written in Paris over a period of seventeen years, and published in 1939, two years before the author's death, Finnegans Wake was Joyce's final work. The book discusses the Earwicker family, comprising the father HCE, the mother Anna Livia Plurabelle (ALP), and their three children Shem the Penman, Shaun the Postman, and Issy.

Patrick McCarthy describes HCE's wife Anna Livia Plurabelle (ALP) as "the river-woman whose presence is implied in the "riverrun" with which Finnegans Wake opens and whose monologue closes the book. For over six hundred pages, Joyce presents Anna Livia to us almost exclusively through other characters. The most extensive discussion of ALP comes in chapter I.8, in which hundreds of names of rivers are woven into the tale of ALP's life, as told by two gossiping washerwomen. Similarly hundreds of city names are woven into "Haveth Childers Everywhere", the corresponding passage at the end of III.3 which focuses on HCE. As a result, it is generally contended that HCE personifies the Viking-founded city of Dublin, and his wife ALP personifies the river Liffey, on whose banks the city was built.>>
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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by alter-ego » Wed Dec 21, 2016 9:59 pm

neufer wrote:
gak2000 wrote:
I am confused by the trajectories that the sun follows each day. In the summer, the sun is near the top of image at either edge and lower in the middle. In the winter, the trajectories curve the other way. Presumably the camera has a wide-angle lens that distorts the image. So, could someone explain the perspective in more detail (i.e. how the celestial sphere is mapped to this 2d image).
  • It appears to be an oblique stereographic projection centered at the latitude/longitude of the observer.
Given the near-equal concave/convex curvatures of the solstice tracks, it looks to me it's centered on 0° declination, and the observer's meridian.
The Stellarium view shows a representative APOD field of view, the solstice sun positions and the celestial coordinate grid for the June solstice.
oblique stereographic projection.jpg
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cindy4444

Re: APOD: Traces of the Sun (2016 Dec 21)

Post by cindy4444 » Wed Dec 21, 2016 10:31 pm

:ssmile: I still do not understand the reason why the top is smaller in the northern hemisphere. In the northern hemisphere, In the summer, (closer to aphelion) , the sun will be south but higher in the sky than in the winter(perihelion). Since at aphelion the earth is moving slower, the big loop must be at the top as you look south to the horizon. There is no way it could be otherwise. In the southern hemisphere you look north at noon (when I assume these measurements are made) to get the position and the lowest point (winter there near aphelion--summer here in the north) will be lower above the northern horizon than it is in the summer. This will make the lower loop bigger as it appears in your pictures. Please, please answer this for me as it is driving me crazy. I will check the answer tomorrow.

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by neufer » Wed Dec 21, 2016 10:41 pm

alter-ego wrote:
The Stellarium view shows a representative APOD field of view, the solstice sun positions and the celestial coordinate grid for the June solstice.
It's bad enough that the trees don't shake or change with season.

But, at least, they should rise up from the projected circle of the horizon and point to zenith.
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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by C0ppert0p » Thu Dec 22, 2016 12:45 am

Brilliant!

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Re: APOD: Traces of the Sun (2016 Dec 21)

Post by stowaway » Thu Dec 22, 2016 5:32 am

OUTSTANDING!!!!!!