Myth or Fact? #31 – The great Wall of China can be seen from the Moon

in #science7 years ago


Welcome my dear Steemian friends to a new episode of Myth or Fact! A series in which we will show that some common believes are myths while others turn out to be true.

“...3, 2 ,1, Lift off!”. Being pressed hard against your seat the rocket takes off. You feel the adrenaline rushing through every single cell of your body. With an insane speed you are on your way towards moon! Don't forget to take Steem with you.

The lunar distance is approximately 385,000 km and it would take you around 3 days to get there. Finally you reached your destination and placed your foot on the surface of the moon. You look towards earth and see the perfect blue marble. What a beautiful view that only very few people in the history of humanity were granted to see live.

And there you see it, China! You know it's China since you can see The great Wall of China. With 6350 km length it's the largest building on earth.

But let's slow down for a second. Can we humans really see buildings from the moon? What's your guess? Today we will discover the truth behind this myth.

Let's go!

Human eyesight

We will talk about the resolution of the human eye and and in short how eyesight works. If you want to know more about the sensation of sight I recommend you to read my post Life Explorers - The Human Senses Part I: Sight.

Our retina has approximately 6 million cones and 120 million rods. When the reflected light hits our retina these cells become active. We have three different type of cone cells, S(-hort), M-(medium) and L-(ong) cones. Short, medium and long refer to the wavelength the cell is responding to. The rods however can work with different wavelengths and thus do not matter when it comes to color. They are responsible for brightness and become active when there is less light. While the cones are active and working we speak of photopic vision, responsible for color sight. Scotopic vision is the terminus for sight in low light and only seeing in shades of gray.

Fig. 1 Eye and retinal profile. Source: Kevinmd

As described the human retina has three kinds of cones. Each sensitive to a different wavelength. The following illustrations depicts the relation of wavelength and cones. These three cones together make it possible that we see colors. By combining cones we are able to see over 200 million different colors.

Fig. 2 Spectral sensitivity of the receptor (rods and cones). Source: Wikibooks; Sensory Systems

What really matters it the resolution of the human eye, the distinguishability of very fine structures and the visual acuity. If you have been to a eye doctor you might know this chart with letters. They become smaller and smaller and you will notice it becomes harder and harder to identify the letters. This has something to do with your acuity.


Fig. 3 Snellen chart Source

Acuity is a property of our cones. The area on the retina with the highest density of cones is called fovea and is in the center of the retina. This is the spot where we have the highest acuity and see the sharpest. The acuity drops radically from there.


Fig. 4 Acuity of human eye Source

To keep it simple: It's is not possible to see any buildings on earth. The limiting factor is the resolution of the human eye. In Fact you won't even be able to see specific countries. From a distance of over 380,000 km all you can see is blue and white. The clouds would make it more or less impossible to see the buildings, besides they are too small to be seen.

Charles M. Duke (Apollo 16) and Eugene A. Cernan (Apollo 17) both confirmed they were not able to see any structures from the moon.


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Thanks for reading this episode of Myth or Fact! If you enjoyed it feel free to resteem and leave a comment! I would love to know what you think about todays episode!

Do you love photography? Then I hope you didn't miss my recent MyPictureSunday Episode where I went to Paris. You can see it here MyPictureSunday#10 - Last day in Paris + MyPictureDay Challenge Round #3. You should participate in the contest and win some Steem Power!

Yours,
Tim

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I hope one-day to have enough money to travel to China and have a good tourist visit

Don't worry , soon China will come to you, they are taking over the world. Give them a couple of years and you will see that wall moved at the border with US , Trump wanted a wall ..... The Great wall is coming :))

Actually going to China in 5 days. And as a chinese person I have to say that you are more than welcome. I hope our different customs won't bother you and that you will be able to enjoy our culture to the fullest!

And I hope you will make some great posts. Cheers

great post brother hope ya well

Soon all steemians will be on the moon from booming price of STEEM and BITCOIN... So we will all know sooner then later :)

hahha not so soon. Bitcoin up in 1 year...

Superb creation of the mankind which shows the great civilization of China.

serious shit physics here.....
Save it for tmr to read :)

... ridiculous comment... is this a joke?

What?!
Why r you flagging me?
DID YOU WENT THRU THE POST?

sorry dear but you looked for it... using general language and the word SHIT.

and I went thru the post, did you?

red flag because by your comment well yes, I understand you are telling @timsaid article is some kind of shit.

I meant (serious shit) physics...
come on....
of coz I didn't, I said I'm gonna save it for tmr

@digitalplayer, even if someone is telling this article to be a shit, everyone has the right to put one's opinion. Why this make you to raise a red flag?

so he have the right to tell shit to people and I cannot put red flag? your comment is not consistent my dear...

Well, I probably didn't understand you. Was that the word "shit" which you took it literally and felt offended or was it Johnny's apparent disagreement with the views / facts expressed in the article? I don't think he is telling shit to people but yes, he hasn't come up with his explanations for his stand. May be he wants to say that the arguments put forward to dispel the prevalent myth are not too strong or include some shitty principles of physics and there might be a better way to explain the same thing with better and consistent arguments. Whatever!

But I really feel that there wasn't anything substantial to invoke a red flag. However every one has got their own perception and can exercise their right of raising a red flag. I was just giving my opinion on it. Do as you like.

the advocate of the shit word. nice!!

What happened was @digitalplayer thought you were criticizing the physics when you were just saying the physics was "some serious shit" meaning, so involved you had to save it to come back to.

ya that was exactly what I mean
Thanks for understanding my comment lol

Nice post, I've always wondered about this one!!

Interesting :)

This is a well-argued post. And it's short and to-the-point and nothing superfluous in it.

However, as a series that always trends, and that is important in the popularization of science here on Steemit, I am a bit saddened that it contains so many grammar mistakes! You make a lot of money, so wouldn't it be possible for you to run the article through someone before publishing it? You could pick somebody from Fiverr, for instance, or someone right here on Steemit. It wouldn't take them long, considering how concise your articles are. You could give them 10 SD or whatever, or maybe someone would do it for free. It just seems a shame because your articles are rather good and easy to understand and they promote science.

Anyway, hope this comment doesn't appear impolite!

Followed!

Thanks Tim for saving me a trip to the moon! And for teaching me some interesting facts about vision. @roused

As I people from China, I can tell you that it is a myth!

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