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How We Found Out the Earth Is Round

Carl Sagan tells us how we came about discovering that the earth was not flat but round. This is excerpt from the TV Series "Cosmos".

  • Tada
  • posted by Tada
  • Date 10/26/2009 7:49:47 PM
  • Views: 3078
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Tags Tags: found earth round

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15 Comments

Current View: 15 / Show all Comments

boredPol : LVL 32: VP 4.1: said:

boredPol

Hidden (Show Comment) -39 votes

146 days 8 hours ago...

why this sudden explosion of carl sagan videos? and btw this shadow pattern can be achieved with a flat surface too, put 2 sticks in the ground, put a flashlight above one of them = no shadow, the other one will have shadow...

sato : LVL 31: VP 4: said:

sato

4 votes NegativePositive

146 days ago...

bored the reason for that is that the flashlight is so close. watch again, pay attention to the part where he mentions how far away the sun is and thus what that means about the rays of light coming from it.

pharb : LVL 32: VP 4.1: said:

pharb

7 votes NegativePositive

145 days 23 hours ago...

^^Yeah exactly bored you dipshit! Evidently only dumb shits don`t like Carl Sagan.

boredPol : LVL 32: VP 4.1: said:

boredPol

Hidden (Show Comment) -14 votes

145 days 16 hours ago...

choreboy, tell me where did I mentioned that God of yours in my entry? and I`m sure you think of yourself as a reasonable person, but non of you addressed my explanation, though... just voted me down bc. your messiah told you something different...

delt_osvp : LVL 48: VP 5: said:

delt_osvp

0 votes NegativePositive

145 days 16 hours ago...

boredpaul dont watch the video you douchbag if you dont like it.

2real : LVL 34: VP 4.2: said:

2real

12 votes NegativePositive

145 days 16 hours ago...

BoredPol, first of sato responded to your reasoning, however you may have over looked it. So I`m gonna give you a little more detail, if you look at 5:25 you here him explaining how the sun is so far that the rays which hit earth are parallel, therefore hitting earth with the same angles of light.

Presto : LVL 41: VP 4.9: said:

Presto

2 votes NegativePositive

145 days 14 hours ago...

boredPol if you actually knew what you were talking about you would know that by the time the light from the sun gets to the earth the rays are all parallel. The light from a flashlight is exiting in in a great mess as it bounces off of the reflector.

Carl Sagan is my homeboy. I actually just finished the whole Cosmos series over three days with some friends. We got high as fuck and let our minds get blown over and over.

boredPol : LVL 32: VP 4.1: said:

boredPol

Hidden (Show Comment) -13 votes

145 days 12 hours ago...

delt_osvp "dont read my comment you douchbag if you dont like it." :P

2real Just assuming that all the rays coming to every point on the earth are (mostly) parallel to each other is a stretch. And I`m sorry "he mentions how far away the sun is" is not enough, because it`s not how CS figured it out, but how Eratosthenes did - so a digression how he proved that would be in order. Since Earth is round conclusion rests on this foundation, "because CS said so" is not enough.
I even made a picture http://img504.imageshack.us/img504/5515/proofgu.png
Both of these give same observable data - without information how Eratosthenes tested that light, to tell them apart it feels a little incomplete and based on opinion, not observable data...

Presto See that`s why I used the flashlight in my example, because it would not work with parallel beams (my ex.) - I did not want to complicate it for you saying that I wanted to move the sun closer to earth. And sun is a kind of a flashlight from our point of view. I`m just saying that if it where smaller and closer you could get same effect with two sticks on flat surface if that close sun/flashlight was directly above one of them. And you would get the same observation as with a far away sun and round Earth. You can`t just assume that all light is parallel in every place on Earth at the same time. And that`s what is missing from his argument. I assume it was there, but CS decided not to mention it, because of the available time and/or viewers would not notice anyway - and so you didn`t ;-) btw light coming from the sun is not perfectly parallel either. But I don`t want to nitpick.
You see it`s nothing new for me, I heard it all before in my science, geography and history class a long, long, long time ago in my primary school, so these videos are quite boring, obvious and definitely nowhere near "mind blowing". You can`t just assume "light is parallel everywhere on earth at the same time" and build arguments on that, because it`s bad science (I`m not saying they did not do it, but it would be worth mentioning that they did, because if they didn`t the flashlight/close_sun explains it equally well)!


"if you actually knew what you were talking about you would know that by the time the light from the sun gets to the earth the rays are all parallel. The light from a flashlight is exiting in in a great mess as it bounces off of the reflector. "
And that`s what I`m using in my thought experiment, a smaller/closer sun starts acting more like a flashlight/light bulb (something you can relate to) and could explain the two shadows just as well. Now, I don`t know about you but I don`t like to choose one over the other on a feeling, but on what did Eratosthenes do to tell them apart. :-)
A good advice for the future - person that gets his "mind get blown over and over" by a TV digest of *BASIC* knowledge should not use "if you actually knew what you were talking about" ;-)

Rikaru : LVL 13: VP 2.2: said:

Rikaru

6 votes NegativePositive

145 days 6 hours ago...

Fine bored, you want to know how they knew that sunlight lands parallel to the earth? Here`s a simple mental experiment. Using the hypothesis that the earth might be round, assume that they know that the sun rises in the east and sets in the west. (They built the pyramid faces within 1 degree of the cardinal directions, so they more than likely had concept of them) If the sun is small and close, you would expect that nights would be considerably longer than the day (I would guess about a 4 hour swing in time; days would be roughly 10 hours long on average, nights 14).

If you`re having trouble visualizing this, take that trusty flashlight of yours and shine it on a beach ball, the closer you get, the less of the ball will be lit up, hence longer nights.

To summarize, IF the earth is round, sunlight must hit the earth parallel (as a generality, not random deflected light), because days are as long as nights.

boredPol : LVL 32: VP 4.1: said:

boredPol

Hidden (Show Comment) -8 votes

145 days 5 hours ago...

Rikaru
> "If the sun is small and close, you would
> expect that nights would be considerably
> longer than the day"

Well the length of day/night is not equal and their ratio shifts during the year. Today where I live the night was longer than the day. ...I thought you there trying to disprove that "if" bit? ;-)

Rikaru
>"If you`re having trouble visualizing this,
> take that trusty flashlight of yours and
> shine it on a beach ball, the closer you
> get, the less of the ball will be lit
> up, hence longer nights."

Well I was thinking more like few times as far as the moon, since from the moon you can basically observe almost all there is on the half facing you.

Rikaru
>"To summarize, IF the earth is round,
> sunlight must hit the earth parallel
> (as a generality, not random deflected
> light), because days are as long
> as nights."

unfortunately for your argument days are generally NOT as long as nights - it depends where on the earth you are :D
http://en.wikipedia.org/wiki/File:Day_length.jpeg

You see it`s harder than it looks - as a hint, the way to smash my close sun (aka. flashlight) argument lies in geometry - calculate where the sun would be based on observable angles if a) the sticks are on flat earth + sun so close that light is not parallel, b) if earth is round and the sun is very far that it seems light is parallel ;-)
I just did, and it`s quite obvious which one is reasonable - you see that`s one of the ways to tell them apart. And from we can see it should be mentioned instead of assumption.

I wish other people voting me down would would try to come up with rebuttal instead of "what he said something was unclear in CS video!? Burn that witch!", btw did you heard about "argument from authority"? :3 Know the reasons behind you believe instead of just being like a religious person that "is religious", but has no idea what`s in the scripture or why they believe.

Rikaru even if your argument was flawed it was still better than anything they had to counter mine, and probablly would fail even more at it.
But good job for trying! And I hope you learned that length of a typical night != length of a typical day (with a room for occasional exception). ;)

atomsk55 : LVL 32: VP 4.1: said:

atomsk55

0 votes NegativePositive

145 days 5 hours ago...

Carl Sagan got the best video screenshots and best auto-tuned voice

Bom Hagan : LVL 37: VP 4.5: said:

Bom Hagan

2 votes NegativePositive

145 days 5 hours ago...

3:53 How did Carl Sagan get his head through that turtleneck

Rikaru : LVL 13: VP 2.2: said:

Rikaru

4 votes NegativePositive

145 days 5 hours ago...

"Well the length of day/night is not equal and it shifts during the year. Today then I woke up the night was longer than the day. ...I thought you there trying to disprove that "if" bit? ;-)"

Again, not paying close enough attention to the video. They said on June 21st. During summer in egypt, amount of daylight in a day averages 12 hours. Don`t believe me? Look it up. So if by some circumstance, the experiment was tried in Alaska or Siberia, the conclusion that light falls on the earth parallel with itself would have been harder to deduce. Since it is in Egypt, close to the equator, this conclusion is much easier to reach.

Once again, for this experiment, for these people, in this location, I summarize. Because in the summer months of Egypt, days are (on average) just as long as nights. However, if the sun were small and close, this would not be the case.

"Well I was thinking more like few times as far as the moon, since from the moon you can basically observe almost all there is on the half facing you."

Now THAT is bad science. You saw a picture, and it was probably from the moon, and you think you can probably maybe see half of the earth?

And please wipe the "know-it-all" smirks from your messages. It ruins any credibility you already don`t have. I know you`re just going to keep arguing a point that isn`t there, but I hope I`m wrong. Please don`t waste my time anymore by introducing "evidence" that I am wrong, even though it is not evidence at all.

For the record, I could do the math for a closer sun and the angles involved, but I`d really rather not spend the time proving something that I already know to be true.

smugdruggler : LVL 35: VP 4.3: said:

smugdruggler

-2 votes NegativePositive

145 days 5 hours ago...

^^i`m just voting you down because I don`t like your tone, which is in many ways more important.

Dannyboy : LVL 29: VP 3.8: said:

Dannyboy

1 votes NegativePositive

145 days 5 hours ago...

What i want to know is, how did he know there`s a shadow 800 kms away from where he`s standing?

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