APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

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APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by APOD Robot » Sun Dec 22, 2019 5:05 am

Image Solstice Illuminated: A Year of Sky

Explanation: Can you find which day is the winter solstice? Each panel shows one day. With 360 movie panels, the sky over (almost) an entire year is shown in time lapse format as recorded by a video camera on the roof of the Exploratorium museum in San Francisco, California. The camera recorded an image every 10 seconds from before sunrise to after sunset and from mid-2009 to mid-2010. A time stamp showing the local time of day is provided on the lower right. The videos are arranged chronologically, with July 28 shown on the upper left, and January 1 located about half way down. In the videos, darkness indicates night, blue depicts clear day, while gray portrays pervasive daytime cloud cover. Many videos show complex patterns of clouds moving across the camera's wide field as that day progresses. The initial darkness in the middle depicts the delayed dawn and fewer daylight hours of winter. Although every day lasts 24 hours, nighttime lasts longest in the northern hemisphere in December and the surrounding winter months. Therefore, finding the panel with the longest night will locate the day of winter solstice -- which happens to be today in the northern hemisphere. As the videos collectively end, sunset and then darkness descend first on the winter days just above the middle, and last on the mid-summer near the bottom.

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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by Ann » Sun Dec 22, 2019 6:42 am

Craters of the Moon. Photo: ISRO.

Who would have thought that the gray skies of the Earth will sometimes look like craters on the Moon?


Days of sky 2.png

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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by navid.mgd@gmail.com » Sun Dec 22, 2019 1:00 pm

Amazing! but I don't get it why the latest dawn is not matched with earliest sunset?

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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by BDanielMayfield » Sun Dec 22, 2019 2:04 pm

navid.mgd@gmail.com wrote:
Sun Dec 22, 2019 1:00 pm
Amazing! but I don't get it why the latest dawn is not matched with earliest sunset?
Just a guess here, but is this an effect of the Earth having an elliptical orbit rather than a perfectly circular one?
"Happy are the peaceable ... "

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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by BDanielMayfield » Sun Dec 22, 2019 2:07 pm

Ann wrote:
Sun Dec 22, 2019 6:42 am
Craters of the Moon. Photo: ISRO.

Who would have thought that the gray skies of the Earth will sometimes look like craters on the Moon?



Days of sky 2.png


Ann
A very weird effect called "raindrops on your lens"?
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by neufer » Sun Dec 22, 2019 2:08 pm

https://www.etymonline.com/search?q=sky wrote:
<<sky (n.) c. 1200, "a cloud," from Old Norse sky "cloud," from Proto-Germanic *skeujam "cloud, cloud cover" (source also of Old English sceo, Old Saxon scio "cloud, region of the clouds, sky;" Old High German scuwo, Old English scua, Old Norse skuggi "shadow;" Gothic skuggwa "mirror"), from PIE root *(s)keu- "to cover, conceal."

Meaning "upper regions of the air" is attested from c. 1300; replaced native heofon in this sense (see heaven). In Middle English, the word can still mean both "cloud" and "heaven," as still in the skies, originally "the clouds."
>>
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by Whiskybreath » Sun Dec 22, 2019 2:10 pm

Well, that was astonishingly dull. Worthy, I suppose, but hardly better than a sequence showing paint drying.

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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by orin stepanek » Sun Dec 22, 2019 2:37 pm

It was interesting; but???? :oops:
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Raindrops keep fallin' on the Moon

Post by Ann » Sun Dec 22, 2019 2:38 pm

BDanielMayfield wrote:
Sun Dec 22, 2019 2:07 pm
Ann wrote:
Sun Dec 22, 2019 6:42 am
Craters of the Moon. Photo: ISRO.
Who would have thought that the gray skies of the Earth will sometimes look like craters on the Moon?

Days of sky 2.png
Ann
A very weird effect called "raindrops on your lens"?
Well, consider the size of the raindrops that must have fallen on the Moon! :shock:

Click to play embedded YouTube video.

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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by neufer » Sun Dec 22, 2019 4:17 pm

Click to play embedded YouTube video.
Whiskybreath wrote:
Sun Dec 22, 2019 2:10 pm

Well, that was astonishingly dull. Worthy, I suppose, but hardly better than a sequence showing paint drying.
Not a whole lot of cumulonimbus action in San Francisco.
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by BDanielMayfield » Sun Dec 22, 2019 4:28 pm

neufer wrote:
Sun Dec 22, 2019 4:17 pm
Click to play embedded YouTube video.
Whiskybreath wrote:
Sun Dec 22, 2019 2:10 pm

Well, that was astonishingly dull. Worthy, I suppose, but hardly better than a sequence showing paint drying.
Not a whole lot of cumulonimbus action in San Francisco.
Yes, but ... [it's been claimed]
Mark Twain wrote:The coldest winter I ever experienced was a summer in San Francisco.
Last edited by BDanielMayfield on Sun Dec 22, 2019 7:53 pm, edited 2 times in total.
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by neufer » Sun Dec 22, 2019 5:58 pm

Code: Select all

Climate: San Francisco
Daily mean °F (Paris)
----------------------
Jan 	51.3 (40.5)
Feb 	53.9 (41.0)
Mar 	55.1 (47.5)
Apr  	56.2 (53.0)
May 	57.6 (59.0)
Jun 	59.6 (64.0)
Jul 	60.3 (68.0)
Aug 	61.6 (68.0)
Sep 	62.7 (62.0)
Oct 	61.5 (54.5)
Nov 	56.6 (46.5)
Dec 	51.6 (41.5)
BDanielMayfield wrote:
Sun Dec 22, 2019 4:28 pm
Mark Twain wrote:
The coldest winter I ever experienced was a summer in San Francisco.
https://www.snopes.com/fact-check/and-never-the-twain-shall-tweet/ wrote:
Did Mark Twain once assert the coldest winter he'd ever spent was a summer in San Francisco?
David Mikkelson wrote:
Searches of Twain writings, private letters, and other publications fail to locate this witticism. The closest resemblance to it appears in an 1879 letter in which Twain quoted a wag who, when asked if he’d ever seen such a cold winter, replied, “Yes, last summer.” Twain then added his own comment, “I judge he spent his summer in Paris.”
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by BDanielMayfield » Sun Dec 22, 2019 7:50 pm

neufer wrote:
Sun Dec 22, 2019 5:58 pm

Code: Select all

Climate: San Francisco
Daily mean °F (Paris)
----------------------
Jan 	51.3 (40.5)
Feb 	53.9 (41.0)
Mar 	55.1 (47.5)
Apr  	56.2 (53.0)
May 	57.6 (59.0)
Jun 	59.6 (64.0)
Jul 	60.3 (68.0)
Aug 	61.6 (68.0)
Sep 	62.7 (62.0)
Oct 	61.5 (54.5)
Nov 	56.6 (46.5)
Dec 	51.6 (41.5)
BDanielMayfield wrote:
Sun Dec 22, 2019 4:28 pm
Mark Twain wrote:
The coldest winter I ever experienced was a summer in San Francisco.
https://www.snopes.com/fact-check/and-never-the-twain-shall-tweet/ wrote:
Did Mark Twain once assert the coldest winter he'd ever spent was a summer in San Francisco?
David Mikkelson wrote:
Searches of Twain writings, private letters, and other publications fail to locate this witticism. The closest resemblance to it appears in an 1879 letter in which Twain quoted a wag who, when asked if he’d ever seen such a cold winter, replied, “Yes, last summer.” Twain then added his own comment, “I judge he spent his summer in Paris.”
(my above comment edited in view of unconfirmed nature of Twainish quotation.)

Wow, I'm a veritable font of uncertainty today. :|
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by alter-ego » Sun Dec 22, 2019 8:06 pm

BDanielMayfield wrote:
Sun Dec 22, 2019 2:04 pm
navid.mgd@gmail.com wrote:
Sun Dec 22, 2019 1:00 pm
Amazing! but I don't get it why the latest dawn is not matched with earliest sunset?
Just a guess here, but is this an effect of the Earth having an elliptical orbit rather than a perfectly circular one?
Only partially.
Earth's obliquity (axis tilt) is the primary contributor to why the days are different for the latest sunrise and earliest sunset. Visualizing the tilted Analemma at sunrise and sunset reveals the answer.
 
 
Analemma - Earliest Sunset &amp; Latest Sunrise.JPG
 
As seen here, only the southern third or so is visible to more clearly show the latest sunrise and earliest sunset about the Winter solstice. It's clear why the days are different. For a circular orbit the Analemma would appear to be a symmetric figure 8, which for that case the number of days separating the latest sunrise and earliest sunset from the solstice would be equal. An elliptical orbit (real case shown here) barely, and subtly, reveals unequal days from the solstice. The analemma shown here is actually for my more northern latitude so its inclination angle is higher than that for San Francisco. Therefore, for a lower Analemma inclination angle, the diagram indicates the latest sunrise and earliest sunsets would be further apart which is indeed the case: For me the latest sunrise occurs 11 days after the solstice and earliest sunset occurs 10 days before the solstice. For San Francisco, it's 16 days and 15 days respectively.

So Earth's elliptical orbit creates and asymmetry in these times by only one day in these cases, but the majority of the difference is due to Earth's obliquity.
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by BDanielMayfield » Sun Dec 22, 2019 8:41 pm

alter-ego wrote:
Sun Dec 22, 2019 8:06 pm
BDanielMayfield wrote:
Sun Dec 22, 2019 2:04 pm
navid.mgd@gmail.com wrote:
Sun Dec 22, 2019 1:00 pm
Amazing! but I don't get it why the latest dawn is not matched with earliest sunset?
Just a guess here, but is this an effect of the Earth having an elliptical orbit rather than a perfectly circular one?
Only partially.
Earth's obliquity (axis tilt) is the primary contributor to why the days are different for the latest sunrise and earliest sunset. Visualizing the tilted Analemma at sunrise and sunset reveals the answer.
 
 Analemma - Earliest Sunset &amp; Latest Sunrise.JPG
 
As seen here, only the southern third or so is visible to more clearly show the latest sunrise and earliest sunset about the Winter solstice. It's clear why the days are different. For a circular orbit the Analemma would appear to be a symmetric figure 8, which for that case the number of days separating the latest sunrise and earliest sunset from the solstice would be equal. An elliptical orbit (real case shown here) barely, and subtly, reveals unequal days from the solstice. The analemma shown here is actually for my more northern latitude so its inclination angle is higher than that for San Francisco. Therefore, for a lower Analemma inclination angle, the diagram indicates the latest sunrise and earliest sunsets would be further apart which is indeed the case: For me the latest sunrise occurs 11 days after the solstice and earliest sunset occurs 10 days before the solstice. For San Francisco, it's 16 days and 15 days respectively.

So Earth's elliptical orbit creates and asymmetry in these times by only one day in these cases, but the majority of the difference is due to Earth's obliquity.
Thanks for that definitive answer alter-ego.
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by alter-ego » Sun Dec 22, 2019 8:52 pm

BDanielMayfield wrote:
Sun Dec 22, 2019 8:41 pm
...
Thanks for that definitive answer alter-ego.
You're welcome.
FYI, I plotted the circular and eccentric analemma components for reference:
 
Analemma Components.JPG
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Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by navid.mgd@gmail.com » Mon Dec 23, 2019 6:56 am

alter-ego wrote:
Sun Dec 22, 2019 8:06 pm
BDanielMayfield wrote:
Sun Dec 22, 2019 2:04 pm
navid.mgd@gmail.com wrote:
Sun Dec 22, 2019 1:00 pm
Amazing! but I don't get it why the latest dawn is not matched with earliest sunset?
Just a guess here, but is this an effect of the Earth having an elliptical orbit rather than a perfectly circular one?
Only partially.
Earth's obliquity (axis tilt) is the primary contributor to why the days are different for the latest sunrise and earliest sunset. Visualizing the tilted Analemma at sunrise and sunset reveals the answer.
 
 Analemma - Earliest Sunset &amp; Latest Sunrise.JPG
 
As seen here, only the southern third or so is visible to more clearly show the latest sunrise and earliest sunset about the Winter solstice. It's clear why the days are different. For a circular orbit the Analemma would appear to be a symmetric figure 8, which for that case the number of days separating the latest sunrise and earliest sunset from the solstice would be equal. An elliptical orbit (real case shown here) barely, and subtly, reveals unequal days from the solstice. The analemma shown here is actually for my more northern latitude so its inclination angle is higher than that for San Francisco. Therefore, for a lower Analemma inclination angle, the diagram indicates the latest sunrise and earliest sunsets would be further apart which is indeed the case: For me the latest sunrise occurs 11 days after the solstice and earliest sunset occurs 10 days before the solstice. For San Francisco, it's 16 days and 15 days respectively.

So Earth's elliptical orbit creates and asymmetry in these times by only one day in these cases, but the majority of the difference is due to Earth's obliquity.
Thank you Alter-ego and Thank you Daniel for elaborating on my question.

guenthert

Re: APOD: Solstice Illuminated: A Year of Sky (2019 Dec 22)

Post by guenthert » Mon Dec 23, 2019 7:11 am

In combination with the music this was quite beautiful.