APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

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APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by APOD Robot » Mon Jun 21, 2010 4:08 am

Image Sunrise Solstice at Stonehenge

Explanation: Today the Sun reaches its northernmost point in planet Earth's sky. Called a solstice, the date traditionally marks a change of seasons -- from spring to summer in Earth's Northern Hemisphere and from fall to winter in Earth's Southern Hemisphere. The above image was taken during the week of the 2008 summer solstice at Stonehenge in United Kingdom, and captures a picturesque sunrise involving fog, trees, clouds, stones placed about 4,500 years ago, and a 5 billion year old large glowing orb. Even given the precession of the Earth's rotational axis over the millennia, the Sun continues to rise over Stonehenge in an astronomically significant way.

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by moonstruck » Mon Jun 21, 2010 4:36 am

I guess I don't get it. The sun rises over stonehenge in an astronomically significant way. What different way? It seems to me like nothing there is really lined up with the sun. What am I missing? :?

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by Chris Peterson » Mon Jun 21, 2010 4:51 am

moonstruck wrote:I guess I don't get it. The sun rises over stonehenge in an astronomically significant way. What different way? It seems to me like nothing there is really lined up with the sun. What am I missing? :?
This image is essentially aesthetic; it doesn't show the relationship between the Sun's position on the solstice and the relevant stones of the henge. There is a pair of stones that point to the position of the rising Sun on the solstice.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by owlice » Mon Jun 21, 2010 7:10 am

You saw it here first! :)
Last edited by owlice on Mon Jun 21, 2010 2:29 pm, edited 1 time in total.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by weborguk » Mon Jun 21, 2010 8:09 am

Um - I think that caption's wrong. It's not precession that alters sunrise/set position at the solstices, it's the change in the obliquity of the ecliptic.

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by orin stepanek » Mon Jun 21, 2010 11:19 am

Chris Peterson wrote:
moonstruck wrote:I guess I don't get it. The sun rises over stonehenge in an astronomically significant way. What different way? It seems to me like nothing there is really lined up with the sun. What am I missing? :?
This image is essentially aesthetic; it doesn't show the relationship between the Sun's position on the solstice and the relevant stones of the henge. There is a pair of stones that point to the position of the rising Sun on the solstice.
I'd like to see the solstice with Stonehenge doing its thing! Now that would be neat! :!:
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by Beyond » Mon Jun 21, 2010 12:39 pm

PBS had Stonehenge "doing its thing" years ago. So we got to see the Sun rising through some Big stones. WHOOPIE :!: Just as much happened then as happens now, as happens every year. NUT'IN.

Owlice -- your link goes to the Observation deck, but i could not find any Stonehenge stuff there.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by rstevenson » Mon Jun 21, 2010 12:51 pm

moonstruck wrote:I guess I don't get it. The sun rises over stonehenge in an astronomically significant way. What different way? It seems to me like nothing there is really lined up with the sun. What am I missing? :?
I believe you have to be inside it to "get it." That is, the portentous alignments occur only to viewers located at or near the middle of the rings or stones.

Depending on your needs and leanings, you can think of Stonehenge and other such devices worldwide as either calendars or cathedrals. I suppose they served both purposes.

Rob

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by neufer » Mon Jun 21, 2010 1:34 pm

weborguk wrote:Um - I think that caption's wrong. It's not precession that alters sunrise/set position at the solstices, it's the change in the obliquity of the ecliptic.
Indeed. It all depends on where the Arctic circle lies.

And the azimuth angular change over 4500 years only amounts to
about 35 minutes of arc or about the width of the sun itself.
  • --------------------------------------------------------------
    "Azimuth" of rising/setting sun at summer solstice
    ~ arc sin(Latitude/Arctic Circle Lat.)

    Latitude of Stonehenge = 51.179ºN

    Arctic circle circa 2000 AD = 66.561ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.256º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.256º
    .....................................................
    Arctic circle circa 2500 BC = 66.000ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.845º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.845º
    --------------------------------------------------------------
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by Bearmum » Mon Jun 21, 2010 2:21 pm

Guys, the Solstice does not mark the beginning of summer. It marks Mid-summer -- as in Midsummer's Day. After Solstice, the days get shorter. The tipping point between Spring and Summer is closer to the Equinox.

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by owlice » Mon Jun 21, 2010 2:30 pm

beyond wrote:Owlice -- your link goes to the Observation deck, but i could not find any Stonehenge stuff there.
Thanks, beyond! I've fixed the link; it takes one to this thread, on which today's APOD image appears.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by Chris Peterson » Mon Jun 21, 2010 2:32 pm

Bearmum wrote:Guys, the Solstice does not mark the beginning of summer. It marks Mid-summer -- as in Midsummer's Day. After Solstice, the days get shorter. The tipping point between Spring and Summer is closer to the Equinox.
"Summer" (and the other seasons) are civil distinctions. Astronomically, they have no starting dates. In practice, temperature and other climatic effects of the seasons lag the solstices and equinoxes by several weeks, so using those days to define the beginning of the seasons makes good sense.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by bystander » Mon Jun 21, 2010 3:14 pm

Bearmum wrote:Guys, the Solstice does not mark the beginning of summer. It marks Mid-summer -- as in Midsummer's Day. After Solstice, the days get shorter. The tipping point between Spring and Summer is closer to the Equinox.
What is the Summer Solstice?
Discovery News | 21 June 2010
Ian O'Neill wrote:Today is a very special day, it's the longest day of the year or the "summer solstice." Often the day just drifts by without even being noticed, but for me, when growing up in southwest England, I always associated solstice with Stonehenge and Druids.

Since studying astronomy at school, I soon realized that the summer solstice -- which occurs on June 20 or 21 each year -- was more than just a date to worship the sun; it's a subtle astronomical phenomenon that underpins all life on Earth.

The science is fairly straightforward: The Earth's axis is tilted by about 23.5 degrees from its orbital plane. In other words, our planet spins around its axis like a spinning top, but its north pole is always "off vertical" by 23.5 degrees.

As the Earth orbits the sun, the North Pole is pointing preferentially toward the sun during the summer in the northern hemisphere (now), but points away 6 months later on December 20 or 21. For the northern hemisphere, when the north pole is tilted toward the sun, it's the summer solstice; when pointing away, it's the winter solstice. For the southern hemisphere, the opposite is true (i.e. when it's the summer solstice in the northern hemisphere, it is the winter solstice in the southern hemisphere).

The summer solstice is the longest day of the year, while the winter solstice is the shortest day of the year.

Also, the summer solstice is the day that the sun can be seen at the highest point in the sky. At the summer solstice, the sun will be directly above the Tropic of Cancer (northern hemisphere) or the Tropic of Capricorn (southern hemisphere). If you are located between the Tropics, the sun will pass overhead (i.e. the zenith) in the run-up to summer solstice. At these latitudes, the sun will be directly overhead at different times of the year depending where you are.

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by neufer » Mon Jun 21, 2010 3:16 pm

Chris Peterson wrote:
Bearmum wrote:Guys, the Solstice does not mark the beginning of summer. It marks Mid-summer -- as in Midsummer's Day. After Solstice, the days get shorter. The tipping point between Spring and Summer is closer to the Equinox.
"Summer" (and the other seasons) are civil distinctions. Astronomically, they have no starting dates. In practice, temperature and other climatic effects of the seasons lag the solstices and equinoxes by several weeks, so using those days to define the beginning of the seasons makes good sense.
Summer Solstice is the time for maximal heating temperature change of the temperate zone oceans and not of the temperatures themselves. (Or rather the maximal heating temperature change of the temperate zone oceans precedes Summer Solstice by about two weeks because the cooler ocean temperatures were radiating away less of that energy then.)

The cumulative effect of this seasonal heating results in sea surface temperature & Atlantic hurricane maximums around September 10 (at about a quarter of a cycle lag time). The further away one is from oceans and other large bodies of water (or ice) the closer one gets to the air temperature maximum being near Summer Solstice itself. Meteorological summer begins on June 1 (also the start of hurricane season).

Image
Last edited by neufer on Mon Jun 21, 2010 3:29 pm, edited 4 times in total.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by weborguk » Mon Jun 21, 2010 3:21 pm

neufer wrote:
  • --------------------------------------------------------------
    "Azimuth" of rising/setting sun at summer solstice
    ~ arc sin(Latitude/Arctic Circle Lat.)

    Latitude of Stonehenge = 51.179ºN

    Arctic circle circa 2000 AD = 66.561ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.256º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.256º
    .....................................................
    Arctic circle circa 2500 BC = 66.000ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.845º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.845º
    --------------------------------------------------------------
Have you got a source for the calc you used? I think there's something wrong with those figures - if the axial tilt was 24.000 deg (arctic circle lat 66.000) in 2500BC, then the northernmost sunrise would have to have a smaller azimuth than when the tilt is 23.439 deg (arctic circle lat 66.561) in 2000AD, not a larger one. Assuming you mean azimuth in the traditional sense (ie deg eastwards from north).

Your figures would imply the rising Sun has moved to the 'left' (towards the north) between 2500BC and 2000AD, whereas surely it's moved to the 'right' (towards the east)? Unless I'm visualising the illumination of a tilted Earth completely wrongly.

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by neufer » Mon Jun 21, 2010 3:37 pm

weborguk wrote:
neufer wrote:
  • --------------------------------------------------------------
    "Azimuth" of rising/setting sun at summer solstice
    ~ arc sin(Latitude/Arctic Circle Lat.)

    Latitude of Stonehenge = 51.179ºN

    Arctic circle circa 2000 AD = 66.561ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.256º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.256º
    .....................................................
    Arctic circle circa 2500 BC = 66.000ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.845º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.845º
    --------------------------------------------------------------
Have you got a source for the calc you used? I think there's something wrong with those figures - if the axial tilt was 24.000 deg (arctic circle lat 66.000) in 2500BC, then the northernmost sunrise would have to have a smaller azimuth than when the tilt is 23.439 deg (arctic circle lat 66.561) in 2000AD, not a larger one. Assuming you mean azimuth in the traditional sense (ie deg eastwards from north).

Your figures would imply the rising Sun has moved to the 'left' (towards the north) between 2500BC and 2000AD, whereas surely it's moved to the 'right' (towards the east)? Unless I'm visualising the illumination of a tilted Earth completely wrongly.
I am definitely NOT using "Azimuth" in the traditional sense (ie deg eastwards from north).

I am using "Azimuth" in the sense of
  • 1) degrees north from due east (for sunrise) or
    2) degrees north from due west (for sunset).
Sorry for the confusion.
Art Neuendorffer

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by weborguk » Mon Jun 21, 2010 3:41 pm

Ah, I see - thanks for the clarification.

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by Beyond » Mon Jun 21, 2010 4:43 pm

Uh-oh - It IS the longest day of the year. HORRORS!! That means the days are getting shorter and we are now starting to go downhill to that cold ice-box of winter. Quick! Grab your muckluks and other winter stuff and air them out good in preparation of whats comeing.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by neufer » Mon Jun 21, 2010 5:13 pm

http://www.soulsofdistortion.nl/Summer%20Solstice%20Galactic%20Alignment.html wrote:
<<It is an established fact that Stonehenge was an astronomical observatory for both solar and lunar observations. One of its functions was the determination of the summer solstice date using the summer solstice sunrise. At the 21st of June the rising sun in the North East shines its light in between the Heel Stone onto the Alter Stone at the center of the Trilithons or horseshoe of Stonehenge.>>
Image
http://en.wikipedia.org/wiki/Stonehenge wrote:
<<The Heel Stone lies just outside the main entrance to the henge, next to the present A344 road. It is a rough stone, 16 feet above ground, leaning inwards towards the stone circle. It has been known by many names in the past, including "Friar's Heel" and "Sun-stone". When one stands within Stonehenge, facing north-east through the entrance towards the heel stone, one sees the sun rise above the stone at summer solstice.

Image

A folk tale, which cannot be dated earlier than the 17th century, relates the origin of the Friar's Heel reference.
  • The Devil bought the stones from a woman in Ireland, wrapped them up, and brought them to Salisbury plain. One of the stones fell into the Avon, the rest were carried to the plain. The Devil then cried out, "No-one will ever find out how these stones came here!" A friar replied, "That’s what you think!," whereupon the Devil threw one of the stones at him and struck him on the heel. The stone stuck in the ground and is still there.
Some claim "Friar's Heel" is a corruption of "Freyja's He-ol" from the Nordic goddess Freyja and the Welsh word for track. The Heel Stone lies beside the end portion of Stonehenge Avenue. A more simple explanation for the name might be that the stone heels, or leans.>>
Art Neuendorffer

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by Chris Peterson » Mon Jun 21, 2010 5:25 pm

neufer wrote:
http://www.soulsofdistortion.nl/Summer%20Solstice%20Galactic%20Alignment.html wrote:
<<It is an established fact that Stonehenge was an astronomical observatory for both solar and lunar observations...
You do need to be awfully careful when looking for information about Stonehenge. There are a lot of crazy ideas out there, and a lot of people passionate in their beliefs about the abilities and knowledge of ancient people. In fact, it is not at all certain that Stonehenge was built as an astronomical observatory. It obviously has some astronomically significant alignments, but it is just as likely that the structure was built for some sort of spiritual or religious purpose. Although people have attempted to find complex astronomical alignments, these are very speculative. There may have been far less going on at Stonehenge (from an astronomical viewpoint) than some people would like to believe.
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by Beyond » Mon Jun 21, 2010 7:20 pm

Swainy - Where did the Bubble come from in your 2nd referrence?

Neufer - where did the other heel stone go? C'mon now -- put it back :!:
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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by León » Mon Jun 21, 2010 8:54 pm

In the mountains of nowadays Armenia (in the south, close to town Goris), the first observatory Carahunge (Car-means stone, hunge-means voice, sound) was created. It has a history of 7.500 years and scientists believe, that there is a tight connection between the observatory in Armenia and Stonehenge in Britain Image

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by neufer » Mon Jun 21, 2010 9:20 pm

neufer wrote:
  • --------------------------------------------------------------
    "Azimuth" of rising/setting sun at summer solstice
    ~ arc sin(Latitude/Arctic Circle Lat.)

    Latitude of Stonehenge = 51.179ºN

    Arctic circle circa 2000 AD = 66.561ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.256º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.256º
    .....................................................
    Arctic circle circa 2500 BC = 66.000ºN
    "Azimuth" of rising/setting sun at summer solstice ~ 50.845º
    "Azimuth" of rising/setting sun at winter solstice ~ -50.845º
    --------------------------------------------------------------
These angles based upon the ad hoc equation
[arc sin(Latitude/Arctic Circle Lat.)] are clearly WRONG!

Stonehenge "Azimuth" of rising/setting sun at summer solstice ~ 40º (not ~ 50º)
Equatorial "Azimuth" of rising/setting sun at summer solstice = 23.44º (not = 0º)

{Note: I am using "Azimuth" in the sense of
  • 1) degrees north from due east (for sunrise) or
    2) degrees north from due west (for sunset).}
My old mind is too befuddled right now to work out the correct equations, however. :oops:
Art Neuendorffer

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Re: APOD: Sunrise Solstice at Stonehenge (2010 Jun 21)

Post by weborguk » Tue Jun 22, 2010 7:49 am

neufer wrote: These angles based upon the ad hoc equation
[arc sin(Latitude/Arctic Circle Lat.)] are clearly WRONG!
Thanks again - I didn't want to question you twice, but was also bothered that the "~" was clearly indicating a very large approximation! :-)

Simon

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