APOD: North Celestial Tree (2013 Oct 23)

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APOD: North Celestial Tree (2013 Oct 23)

Post by APOD Robot » Wed Oct 23, 2013 4:06 am

Image North Celestial Tree

Explanation: If you climbed this magnificent tree, it looks like you could reach out and touch the North Celestial Pole at the center of all the star trail arcs. The well-composed image was recorded over a period of nearly 2 hours as a series of 30 second long, consecutive exposures on the night of October 5. The exposures were made with a digital camera fixed to a tripod near Almaden de la Plata, province of Seville, in southern Spain, planet Earth. Of course, the graceful star trails reflect the Earth's daily rotation around its axis. By extension, the axis of rotation leads to the center of the concentric arcs in the night sky. Convenient for northern hemisphere night sky photographers and celestial navigators alike, the bright star Polaris is very close to the North Celestial Pole and so makes the short bright trail in the central gap between the leafy branches.

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Beyond » Wed Oct 23, 2013 4:17 am

Well, it's nice, but I'm kinda missing not seeing a cave. Maybe if it was put into motion, going round and round and round and round and... oh, wait, i think i see a cave forming in the middle.
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by BDanielMayfield » Wed Oct 23, 2013 5:17 am

Beyond wrote:Maybe if it was put into motion, going round and round and round and round and...
Imagine that the Earth's rotation rate was so fast that stars actually looked like this! We'd likely be flung off into space and the Earth might be ripped apart. Aaaahhh... :shock:

Happily, that notion is totally absurd. The Earth's rotation rate is actually slowing down, very slowly. Relax and enjoy the ride. :ssmile:
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Nitpicker » Wed Oct 23, 2013 6:38 am

BDanielMayfield wrote:Imagine that the Earth's rotation rate was so fast that stars actually looked like this! We'd likely be flung off into space and the Earth might be ripped apart. Aaaahhh... :shock:

Happily, that notion is totally absurd. The Earth's rotation rate is actually slowing down, very slowly. Relax and enjoy the ride. :ssmile:
Speak for yourself Bruce. We Australians have always had to hold on for dear life. And the bits of us touching the ground get bitten by poisonous snakes and spiders. Some say they're only trying to hold on to us, but I'm not so sure.

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by wonderboy » Wed Oct 23, 2013 11:42 am

Nitpicker wrote:
BDanielMayfield wrote:Imagine that the Earth's rotation rate was so fast that stars actually looked like this! We'd likely be flung off into space and the Earth might be ripped apart. Aaaahhh... :shock:

Happily, that notion is totally absurd. The Earth's rotation rate is actually slowing down, very slowly. Relax and enjoy the ride. :ssmile:
Speak for yourself Bruce. We Australians have always had to hold on for dear life. And the bits of us touching the ground get bitten by poisonous snakes and spiders. Some say they're only trying to hold on to us, but I'm not so sure.


You said you were Australian, and I literally cannot read your post without it having an accent inside my head. hahah. how weird!
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by FloridaMike » Wed Oct 23, 2013 12:55 pm

Well Composed, I like it. Thanks. BTW: Happy Mole Day Chemistry fans.
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by geckzilla » Wed Oct 23, 2013 1:34 pm

wonderboy wrote:You said you were Australian, and I literally cannot read your post without it having an accent inside my head. hahah. how weird!
I live in New York. You should probably read my posts in a heavy Brooklyn accent from now on. Or you could fuggedabout it.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Chris Peterson » Wed Oct 23, 2013 2:04 pm

BDanielMayfield wrote:Imagine that the Earth's rotation rate was so fast that stars actually looked like this!
No need to imagine. The Earth's rotation rate actually does make the stars look like this. That's why we have this image.
Chris

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by wonderboy » Wed Oct 23, 2013 2:05 pm

geckzilla wrote:
wonderboy wrote:You said you were Australian, and I literally cannot read your post without it having an accent inside my head. hahah. how weird!
I live in New York. You should probably read my posts in a heavy Brooklyn accent from now on. Or you could fuggedabout it.


You now sound like Christopher Walken in my head haha.
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Whistle Spit » Wed Oct 23, 2013 5:18 pm

wonderboy wrote:"I'm so fast that last night I turned off the light switch in my hotel room and was in bed before the room was dark" Muhammad Ali, faster than the speed of light?
Faster than the speed of dark :)

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Anthony Barreiro » Wed Oct 23, 2013 6:14 pm

Chris Peterson wrote:
BDanielMayfield wrote:Imagine that the Earth's rotation rate was so fast that stars actually looked like this!
No need to imagine. The Earth's rotation rate actually does make the stars look like this. That's why we have this image.
Chris, if your retinal afterimages last two hours, you should probably see an opthamologist. Most people's afterimages only last about half a second. If the Earth were rotating this far in half a second, well, I'm not good at math, but it would be pretty darn fast. :lol2:
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Chris Peterson » Wed Oct 23, 2013 6:16 pm

Anthony Barreiro wrote:
Chris Peterson wrote:
BDanielMayfield wrote:Imagine that the Earth's rotation rate was so fast that stars actually looked like this!
No need to imagine. The Earth's rotation rate actually does make the stars look like this. That's why we have this image.
Chris, if your retinal afterimages last two hours, you should probably see an opthamologist. Most people's afterimages only last about half a second. If the Earth were rotating this far in half a second, well, I'm not good at math, but it would be pretty darn fast. :lol2:
It's not my retinas that are involved, but my memory. I constantly notice the apparent rotation of the sky when I'm outside.
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Anthony Barreiro » Wed Oct 23, 2013 9:24 pm

Chris Peterson wrote:
BDanielMayfield wrote:Imagine that the Earth's rotation rate was so fast that stars actually looked like this!
No need to imagine. The Earth's rotation rate actually does make the stars look like this. That's why we have this image.
Chris Peterson wrote:
Anthony Barreiro wrote: Chris, if your retinal afterimages last two hours, you should probably see an opthamologist. Most people's afterimages only last about half a second. If the Earth were rotating this far in half a second, well, I'm not good at math, but it would be pretty darn fast. :lol2:
It's not my retinas that are involved, but my memory. I constantly notice the apparent rotation of the sky when I'm outside.
Oh, I see where the confusion arose. For those of us living at lower elevations, "how things actually look" is commonly understood to mean how they appear at a moment in time, i.e. below the temporal threshold at which discrete events are perceived to be occurring simultaneously. Psychological research consistently shows that for the vast majority of human beings a perceptual moment is some proper fraction of a second. How long is a moment for you? Apparently at least two hours, but is it an entire sidereal day? A year? The 26,000 year precessional wobble of the Earth's axis? And what about stars' proper motions? Doesn't it all become an unintelligible blur at some point? :wink:
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by DickZ » Wed Oct 23, 2013 9:45 pm

Why have I never seen a South pole long exposure?
Having visited Australia many times I know the simple answer.
Still the smear of the galaxy center would be impressive, as would the LMC and the empty pole.

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Cousin Ricky » Wed Oct 23, 2013 9:50 pm

My accent is a mix of St. Thomas, north-central Florida, and Boston. After taking an on-line test, I was declared to be from Philadelphia. :mrgreen:

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Beyond » Wed Oct 23, 2013 9:54 pm

Cousin Ricky wrote:My accent is a mix of St. Thomas, north-central Florida, and Boston. After taking an on-line test, I was declared to be from Philadelphia. :mrgreen:
Image
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Boomer12k » Wed Oct 23, 2013 9:54 pm

OK....NOW, I am dizzy!!!

Nice Picture!

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Boomer12k » Wed Oct 23, 2013 9:57 pm

It reminds me of the old TV show.....TIME TUNNEL....

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Nitpicker » Wed Oct 23, 2013 10:25 pm

DickZ wrote:Why have I never seen a South pole long exposure?
Having visited Australia many times I know the simple answer.
Still the smear of the galaxy center would be impressive, as would the LMC and the empty pole.
I'm curious as to what the simple answer might be. Are we too drunk? Or merely less people South of the Equator?

By the way, the centre of the galaxy is only marginally more visible from the Southern Hemisphere than the Northern, and it isn't particularly close to the South Celestial Pole. It passes daily very close to my zenith, and I'm nearly in the tropics.

But here is an APOD star trail taken from the Earth's South Pole (brrr) looking up at their zenith, the South Celestial Pole:
http://apod.nasa.gov/apod/ap120802.html

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Chris Peterson » Wed Oct 23, 2013 11:01 pm

DickZ wrote:Why have I never seen a South pole long exposure?
Having visited Australia many times I know the simple answer.
Still the smear of the galaxy center would be impressive, as would the LMC and the empty pole.
Search through the APODs and you'll find a number of southern sky star trail images, made from Australia, Chile, Antarctica, Tanzania, maybe more.

Of course, there are many more from the north simply because vastly more people live under northern skies.
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Chris Peterson » Wed Oct 23, 2013 11:02 pm

Anthony Barreiro wrote:Oh, I see where the confusion arose. For those of us living at lower elevations, "how things actually look" is commonly understood to mean how they appear at a moment in time, i.e. below the temporal threshold at which discrete events are perceived to be occurring simultaneously.
Don't try to saddle me with the limitations of your own feeble brain machinery.
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by owlice » Wed Oct 23, 2013 11:22 pm

Do I need to start popping corn?
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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by Nitpicker » Thu Oct 24, 2013 12:06 am

I must admit, I haven't seen too many ground trail images, where an equatorially mounted camera tracks the pin-point stars, and the ground arcs around them. Probably because it isn't considered as aesthetically pleasing to our feeble minds. (Chris might like 'em though.)

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Mach's principle

Post by neufer » Thu Oct 24, 2013 1:39 am

http://en.wikipedia.org/wiki/Mach%27s_principle wrote:
<<Mach's principle (or Mach's conjecture) is the name given by Einstein to an imprecise hypothesis often credited to the physicist and philosopher Ernst Mach. The idea is that the local motion of a rotating reference frame is determined by the large scale distribution of matter, as exemplified by this anecdote: "You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don't move?"

Mach's principle says that this is not a coincidence—that there is a physical law that relates the motion of the distant stars to the local inertial frame. If you see all the stars whirling around you, Mach suggests that there is some physical law which would make it so you would feel a centrifugal force. There are a number of rival formulations of the principle. It is often stated in vague ways, like "mass out there influences inertia here". A very general statement of Mach's principle is "Local physical laws are determined by the large-scale structure of the universe." The basic idea also appears before Mach's time, in the writings of George Berkeley.

Newton tried to demonstrate that one can always decide if one is rotating with respect to the absolute space, measuring the apparent forces that arise only when an absolute rotation is performed. If a bucket is filled with water, and made to rotate, initially the water remains still, but then, gradually, the walls of the vessel communicate their motion to the water, making it curve and climb up the borders of the bucket, because of the centrifugal forces produced by the rotation. Newton says that this thought experiment demonstrates that the centrifugal forces arise only when the water is in rotation with respect to the absolute space (represented here by the earth's reference frame, or better, the distant stars); instead, when the bucket was rotating with respect to the water no centrifugal forces were produced, this indicating that the latter was still with respect to the absolute space. “Ernst Mach debunked this notion of absolute space and argued that the inertia existed because the water was spinning relative to the rest of the matter in the universe. Indeed, the same effects would be observed if the bucket was still and the rest of the universe was rotating around it, he said.

This concept was a guiding factor in Einstein's development of the general theory of relativity. Einstein realized that the overall distribution of matter would determine the metric tensor, which tells you which frame is rotationally stationary. Frame dragging and conservation of gravitational angular momentum makes this into a true statement in the general theory in certain solutions. But because the principle is so vague, many distinct statements can be (and have been) made which would qualify as a Mach principle, and some of these are false. The Gödel rotating universe is a solution of the field equations which is designed to disobey Mach's principle in the worst possible way. In this example, the distant stars seem to be revolving faster and faster as one moves further away. This example doesn't completely settle the question, because it has closed timelike curves.

Most physicists believe Mach's principle was never developed into a quantitative physical theory that would explain a mechanism by which the stars can have such an effect. Although Einstein was intrigued and inspired by Mach's principle, Einstein's formulation of the principle is not a fundamental assumption of general relativity. There have been attempts to formulate a theory which is more fully Machian, such as Brans–Dicke theory, but most physicists argue that none have been fully successful.>>
Walter Isaacson, Einstein wrote: <<“The Olympia Academy’s reading list included some classics with themes that Einstein could appreciate, such as Sophocles’ searing play about the defiance of authority, Antigone, and Cervantes’ epic about stubbornly tilting at windmills, Don Quixote. But mostly the three academicians read books that explored the intersection of science and philosophy: David Hume’s A Treatise of Human Nature, Ernst Mach’s Analysis of the Sensations and Mechanics and Its Development, Baruch Spinoza’s Ethics, and Henri Poincaré’s Science and Hypothesis. It was from reading these authors that the young patent examiner began to develop his own philosophy of science.”

“Einstein had two scientific heroes he had never met—Ernst Mach (February 18, 1838 – February 19, 1916) and Hendrik Lorentz—and he was able to visit them both before his move to Prague. When he went to Vienna for his formal presentation to the ministers there, he called on Mach, who lived in a suburb of that city. The aging physicist and preacher of empiricism, who so deeply influenced the Olympia Academy and instilled in Einstein a skepticism about unobservable concepts such as absolute time, had a gnarly beard and gnarlier personality. “Please speak loudly to me,” he barked when Einstein entered his room. “In addition to my other unpleasant characteristics I am also almost stone deaf.””

“As a young empiricist, excited by his readings of Ernst Mach, Einstein had been willing to reject any concepts that could not be observed, such as the ether and absolute time and space and simultaneity. But the success of his general theory convinced him that Mach’s skepticism, even though it might be useful for weeding out superfluous concepts, did not provide much help in constructing new theories.”

“Meanwhile, another approach to quantum mechanics had been developed in the summer of 1925 by a bright-faced 23-year-old hiking enthusiast, Werner Heisenberg, who was a student of Niels Bohr in Copenhagen and then of Max Born in Göttingen. As Einstein had done in his more radical youth, Heisenberg started by embracing Ernst Mach’s dictum that theories should avoid any concepts that cannot be observed, measured, or verified. For Heisenberg this meant avoiding the concept of electron orbits, which could not be observed.”
>>
Art Neuendorffer

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Re: APOD: North Celestial Tree (2013 Oct 23)

Post by rstevenson » Thu Oct 24, 2013 3:24 pm

In the midst of studying Wordsworth's autobiographical "Prelude" I came across this particularly apt bit...
And all the shadowy banks, on either side,
Came sweeping through the darkness, spinning still
The rapid line of motion; then at once
Have I, reclining back upon my heels,
Stopp'd short, yet still the solitary Cliffs
Wheeled by me, even as if the earth had roll'd
With visible motion her diurnal round;
Behind me did they stretch in solemn train
Feebler and feebler, and I stood and watch'd
Till all was tranquil as a dreamless sleep.
Rob