Free planetarium

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Watsisname
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02 Sep 2017 17:11

Solaris wrote:
Source of the post One time, a group of dolfins came close to the boat and start playing around it as they like to do, it was night time, and something so eerie happened, as the dolfins swim, the Noctiluca Scintillans is being disrupted and a trail of light appear on and behind the dolfins. I could clearly saw their shape and the path they had took for few short secs, and when they dived deep down, the trail followed. The sea was pitch black and they were moving around in 3d surrounded by this electrical blue sparkling color. They played for few minutes and leaved. it was one surreal and magic moment.

Awesome story -- that surely must have been one of the most amazing of experiences. :) To me I find it an even more powerful than a good aurora display.  Especially since it's so interactive and right there.  No matter how many times I see it, it always startles and slightly unnerves me when I'm going through the pitch black water under a serene starry sky, and all of a sudden the water explodes with these lights.  It's beautiful but also strikes some kind of primal fear, and I imagine what it must be like to be a creature in the deep ocean, content to be in darkness until a glowing nightmare predator materializes right next to you.
 
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midtskogen
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22 Sep 2017 21:02

I was in Beijing this week.  I had to present a paper to get it published (IEEE/ICIP2017).  So I went to see a section of the Great Wall, which is compulsory, I guess.  The hike along a non-restored section of the wall was actually much more enjoyable than the restored section which was just crowded.
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A-L-E-X
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23 Sep 2017 00:41

midtskogen wrote:
I was in Beijing this week.  I had to present a paper to get it published (IEEE/ICIP2017).  So I went to see a section of the Great Wall, which is compulsory, I guess.  The hike along a non-restored section of the wall was actually much more enjoyable than the restored section which was just crowded.
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The Great Wall is the only artificial structure you can see from the moon :-)
 
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DoctorOfSpace
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23 Sep 2017 10:15

A-L-E-X, I don't think that is true, the great wall is long but not wide, our modern cities are far larger artificial structures and you can't even see them from the moon.
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Mosfet
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23 Sep 2017 10:26

"Time is illusion. Lunchtime doubly so". Douglas N. Adams
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Watsisname
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23 Sep 2017 22:20

For fun let's do the math.  The Moon is about 362,000km away from Earth, at its closest.  The human eye can resolve details down to about 1 arcminute.  At 362,000km, 1 arcminute is about 105km.  The wall is only about 6m wide at its base -- more than 10,000 times too thin to see from the Moon!  There's no way you could spot it with the eye.

What would it take to view it from the Moon?  A telescope at least 30 meters in diameter!

How close would you have to be to expect to just begin to see it?  6m takes up 1 arcminute at about 20km distance.  So the wall is about a factor of 10 times too thin to see from Low Earth Orbit.  That's why specific lighting conditions (like casting long shadows as the Scientific American article reports) are needed to even barely make it out from orbit.

Anyway, @midtskogen those are great photos.  It must have been neat to walk along such ancient architecture -- both restored and not. :)  

I saw the Terracotta Warriors last month when they were on exhibit in Seattle.  It is amazing what people were capable of doing back then under the direction of an emperor like that -- whether for good or ill.
 
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midtskogen
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24 Sep 2017 02:16

The wall is narrow, much narrower than a regular 2 lane highway.  However, the length of the wall is much over the resolving limit of 105 km, so one could say that it spans a distance much greater than what can see from the Moon, though the structure itself is far from visible (no more visible than my house). Unlike roads which also span much longer distances, this is a elevated structure, though most of it is now just rubble.  The unrestored section that I walked is from the 14th century, and though the history of the wall goes back much longer, the ancient parts are either replaced or for practical purposes now gone.

The most impressive thing about this wall is its location.  Much is in difficult terrain, and building it without nearby infrastructure is quite an accomplishment.
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