APOD: Solstice at Newgrange (2008 Dec 20)

[apodman]

http://apod.nasa.gov/apod/ap081220.html

These days the fashion is to talk about the seasons and when they begin meteorologically and climatically as opposed to astronomically. So what? You're not going to find regularly spaced fixed dates (from pagan calendars or otherwise) that fit all seasons or all latitudes, let alone all seasons and all latitudes. So let's just stick with the old view: (1) here are the astronomical equinoxes and solstices; (2) there is seasonal lag that varies in timing, character, and magnitude depending on location.

But the winter solstice in either hemisphere, for anyone living far enough from the equator to notice, is an important event in the mass psyche. Nobody feels it when we go over the hump at the summer solstice and the days start to become slightly shorter. But the winter solstice means the return of light. It is a boost to the soul. We can soon put away our show of lights; we will have dazzled ourselves through the dark times and successfully beckoned the return of the sun. We will have put our foot down and said we are not going to put up with this darkness, and nature will have submitted. One small problem, though: more daylight means less night-time for astronomical observation. Still I'll take the sun.

Rather than climate, here is my favorite solstice topic: http://www.gsfc.nasa.gov/scienceques2005/20060203.htm - Goddard Space Flight Center (NASA) / Science Question of the Week: Do the dates for the latest sunrise and earliest sunset during the winter occur at nearly the same time for all latitudes?

[Chris Peterson]

But the winter solstice in either hemisphere, for anyone living far enough from the equator to notice, is an important event in the mass psyche. Nobody feels it when we go over the hump at the summer solstice and the days start to become slightly shorter. But the winter solstice means the return of light. It is a boost to the soul. We can soon put away our show of lights; we will have dazzled ourselves through the dark times and successfully beckoned the return of the sun. We will have put our foot down and said we are not going to put up with this darkness, and nature will have submitted. One small problem, though: more daylight means less night-time for astronomical observation. Still I'll take the sun.

Believe me, many astronomers do feel it in their psyche when the summer solstice hump is crossed, and they can see the possibility of nighttime observation returning. <g>

Still, your point is taken. The winter holiday my family celebrates is solstice; in spite of being very nonspiritual people, there's nevertheless something very primal about the reversal of the Sun's movement and the sense of celebrating what is probably the oldest recognized "special day".

From dipper's Archer of the Milky Way
To twinkling Twins in starry Gemini,
Our Sun climbs slowly northward, day by day,
Past stars that shine unseen in azure sky.

From Archer unto Capricornus, and
Aquarius to coupled Pisces when
The month of March is reigning o'er the land,
And nature, roused by spring, awakes again.

From Pisces to the Ram, our Sun ascends,
To Taurus and at length to Gemini
When, lingering, the springtime season ends,
And Vega beams like herald of July.

From sear December unto verdant June,
Our Sun shines higher with each passing noon.

-Charles Nevers Holmes, presented at a Mt. Wilson astronomical conference in 1923

[neufer]

I'm shocked, shocked I tell, you to find religion being discussed here!

[apodman]

I'm shocked ... to find religion being discussed here!

Before the Julian calendar was replaced by the Gregorian calendar in the 1300s, the longest night/shortest day of the year was 13 December.

This link describes the origin of the Festival of Lights (St. Lucia's Day - December 13) in Sweden. If not for "us" Swedes getting an early start on the sun beckoning business, the rest of you might never get it to return. It's kinda like setting our ignition timing a few degrees before top dead center.

---

Notwithstanding the reference to the "1300s" above ...

The last day of the Julian calendar was Thursday, 4 October 1582 and this was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (the cycle of weekdays was not affected).

...

Sweden's relationship with the Gregorian Calendar was a difficult one. Sweden started to make the change from the Julian calendar and towards the Gregorian calendar in 1700, but it was decided to make the (then 11-day) adjustment gradually, by excluding the leap days (29 February) from each of 11 successive leap years, 1700 to 1740. In the meantime, the Swedish calendar would be out of step with both the Julian calendar and the Gregorian calendar for 40 years; also, the difference would not be constant but would change every 4 years. This strange system clearly had great potential for endless confusion when working out the dates of Swedish events in this 40-year period. To make matters worse, the system was poorly administered and the leap days that should have been excluded from 1704 and 1708 were not excluded. The Swedish calendar (according to the transition plan) should now have been 8 days behind the Gregorian, but was still in fact 10 days behind. King Charles XII recognised that the gradual change to the new system was not working, and he abandoned it.

However, rather than proceeding directly to the Gregorian calendar, it was decided to revert to the Julian calendar. This was achieved by introducing the unique date 30 February in the year 1712, adjusting the discrepancy in the calendars from 10 back to 11 days. Sweden finally adopted the Gregorian calendar in 1753, when Wednesday, 17 February was followed by Thursday, 1 March. Since Finland was under Swedish rule at that time, it did the same.

Too much for me without my decoder ring and slide rule. I just accept that the festival ended up on the 13th.

[neufer]

http://antwrp.gsfc.nasa.gov/apod/ap081220.html

<<Explanation: Tomorrow's solstice marks the southernmost point of the Sun's annual motion through planet Earth's sky and the astronomical beginning of winter in the north. You can watch a live webcast of the the solstice sunrise from the megalithic tomb of Newgrange, in County Meath, Ireland. Newgrange dates to 5,000 years ago, much older than Stonehenge, but also with accurate alignments to the solstice Sun. In this view from within the burial mound's inner chamber, the first rays of the solstice sunrise are passing through a box constructed above the entrance and shine down an 18 meter long tunnel to illuminate the floor at the foot of a decorated stone.

The actual stone itself would have been directly illuminated by the solstice Sun 5,000 years ago.>>
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http://en.wikipedia.org/wiki/Newgrange
<<Once a year, at the winter solstice, the rising sun shines directly along the long passage into the chamber for about 17 minutes and illuminates the chamber floor. This alignment is too precise to have occurred by chance. Professor M. J. O'Kelly was the first person in modern times to observe this event on December 21, 1967.

The sun enters the passage through a specially contrived opening, known as a roofbox, directly above the main entrance. Although solar alignments are not uncommon among passage graves, Newgrange is one of few to contain the additional roofbox feature. The alignment is such that although the roofbox is above the passage entrance, the light hits the floor of the inner chamber.

Today the first light enters about four minutes after sunrise,
but calculations based on *the precession of the Earth* show that 5000 years ago first light would have entered exactly at sunrise. The solar alignment at Newgrange is very precise compared to similar phenomena at other passage graves such as Dowth or Maes Howe in the Orkney islands, off the coast of Scotland.>>
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It is NOT the [25,765 year cycle] precession of the equinoxes but
rather the [41,013 year cycle] variable obliquity of the axial tilt
that prevents the earth's winter solstice sunrise from occurring at
a point as far south (and as late in the morning) as it did 5000 years ago.

Hence: Today the first light enters about four minutes after sunrise
; too late for: the actual stone itself to be directly illuminated.
.................................................
http://en.wikipedia.org/wiki/Axial_tilt

<<The Earth currently has an axial tilt of about 23.44°.

The Earth's axial tilt varies between 22.63° to 24.35°, with a 41,013-year period, and at present, the tilt is decreasing.

The last maximum was reached in 8700 BC, the mean value occurred around 1550 and the next minimum will be in 11800.

Other planets may have a variable obliquity too, for example on Mars the range is believed to be between 15° and 35°, as a result of gravitational perturbations from other planets. The relatively small range for the Earth is due to the stabilizing influence of the Moon, but it will not remain so. According to Ward, the orbit of the Moon (which is continuously increasing due to tidal effects) will have gone from the current 60 to approximately 66.5 Earth radii in about 1.5 billion years. Once this occurs, a resonance from planetary effects will follow, causing swings of the obliquity between 22° and 38°. Further, in approximately 2 billion years, when the Moon reaches a distance of 68 Earth radii, another resonance will cause even greater oscillations, between 27° and 60°. This would have extreme effects on climate.>>
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[bystander]

<<... Other planets may have a variable obliquity too, for example on Mars the range is believed to be between 15° and 35°, as a result of gravitational perturbations from other planets. The relatively small range for the Earth is due to the stabilizing influence of the Moon, but it will not remain so. According to Ward, the orbit of the Moon (which is continuously increasing due to tidal effects) will have gone from the current 60 to approximately 66.5 Earth radii in about 1.5 billion years. Once this occurs, a resonance from planetary effects will follow, causing swings of the obliquity between 22° and 38°. Further, in approximately 2 billion years, when the Moon reaches a distance of 68 Earth radii, another resonance will cause even greater oscillations, between 27° and 60°. This would have extreme effects on climate.>>

I fully expect to have moved to a more stable habitat by then.

[neufer]

<<... Other planets may have a variable obliquity too, for example on Mars the range is believed to be between 15° and 35°, as a result of gravitational perturbations from other planets. The relatively small range for the Earth is due to the stabilizing influence of the Moon, but it will not remain so. According to Ward, the orbit of the Moon (which is continuously increasing due to tidal effects) will have gone from the current 60 to approximately 66.5 Earth radii in about 1.5 billion years. Once this occurs, a resonance from planetary effects will follow, causing swings of the obliquity between 22° and 38°. Further, in approximately 2 billion years, when the Moon reaches a distance of 68 Earth radii, another resonance will cause even greater oscillations, between 27° and 60°. This would have extreme effects on climate.>>

I fully expect to have moved to a more stable habitat by then.

Coward!
--------------------------------------------------------
http://www.planetary.org/blog/article/00001779/

<<Peter Smith went on to explain what can raise [Mars's] relative humidity to levels where adsorbed water starts doing interesting things, chemically speaking. As I've mentioned before, the tilt of Mars' rotation axis, which is referred to as Mars' obliquity, can vary a lot over a period of many thousands of years. Today, it's about 25 degrees, similar to Earth's tilt, but Mars' obliquity swings from 10 to 40 degrees and sometimes even more.

When the obliquity is very high, summers are long and intense, as the pole is pointed much farther toward the Sun at high summer than it is today. "Once the obliquity gets beyond 35 degrees, the polar cap becomes unstable. It releases water as fast as the atmosphere can accept it. Conditions get very, very humid, and water gets transported past our landing site to the equator. This changes climate dramatically."

With all the extra water in the air, the films of water adsorbed on the soil grains get much thicker, and even though the temperature may still not rise above the freezing point of water, you can get some chemistry happening in the soil that you would ordinarily think of as happening only in the presence of liquid water. "There's no clear evidence that at high obliquity you get liquid water," Zent said. "But you don't really need it to do a lot of things you associate with liquid water, like chemical processing. And there are microbes [on Earth] that live quite happily in that, because they can get nutrients and make waste and do other things in these thin films of water. So this is kind of a key way in which we think that the results from Phoenix might point towards a little bit more activity in the past 100,000 years or so than we see right now.">>
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[bystander]

Coward!

Not at all. I figure to get out while property values are still high. Besides, in another couple of billion years after the earth goes on tilt, conditions in the neighborhood will become intolerable when our neighbor, the Sun, enters old age and begins to expand uncontrollably. Can't see any point in waiting around.

[neufer]

Coward!

Not at all. I figure to get out while property values are still high.

Oh Yeah,...well that's what the folks at Newgrange
& Alpha Regio [Venus] thought before the pancake dome market bubble burst:

<<This Venus image shows a chain of pancake domes east of Alpha Regio. Each dome is roughly 25 km (15 miles) wide, and the highest are about 750 m tall. As in Eistla Regio, most of these domes show a (very) small central pit. Here, however, we see a variety of crack patterns on the domes. These probably mark small changes in the speed or conditions of eruption. Many of the domes here also overlap. Such overlaps are quite common, and most seem to mark a series of dome eruptions. In some cases, however, they may mark two domes that formed at the same time.>>

Besides, in another couple of billion years after the earth goes on tilt, conditions in the neighborhood will become intolerable
when our neighbor, the Sun, enters old age and begins to expand uncontrollably. Can't see any point in waiting around.

I've entered old age and have begun to expand uncontrollably; so does that make me a bad neighbor?

[BMAONE23]

(snip)
I've entered old age and have begun to expand uncontrollably; so does that make me a bad neighbor?

Only if you experience sudden and uncontrolable expansion into the passenger in the airline seat next to you.

[bystander]

I've entered old age and have begun to expand uncontrollably; so does that make me a bad neighbor?

Only if you plan on boiling off all our water and loosing our atmosphere into space.

[BMAONE23]

I've entered old age and have begun to expand uncontrollably; so does that make me a bad neighbor?

Only if your uncontrolled expansion rate is greater than entropy

[neufer]

I know a dwarf Star who has entered old age and begun to expand uncontrollably
& turn bright red who may not be visiting BMAONE23 or bystander this year. 8)

[davenjohn]

I like all the winter activities with superb warm clothing... but....