How the traditional Greeks knew the Earth was spherical. All you want is sticks, eyes, toes and brains.

40 Comments

1. Carl Sagan, Neil tries too hard to be like him but there will never be another Carl Sagan in our life time

2. Sagan. What a national treasure…

   The Mr.Rogers of science.

3. How did they measure the shadows at the same time without real time communications?

4. Flat Earther’s: *”I’m going to ignore that.”*

5. Eratosthenes then measured the angle of a shadow cast by a stick at noon on the summer solstice in Alexandria, and found it made an angle of about 7.2 degrees, or about 1/50 of a complete circle. He realized that if he knew the distance from Alexandria to Syene, he could easily calculate the circumference of Earth.

6. How the heck were they so smart back then. No Internet, no geography books. Very impressive

7. I don’t think many people nowadays have the last one.

8. For those asking:

   A detail left out is that he did this on the summer solstice. It was known that at noon on the solstice in Syene such an obelisk would cast no shadow. This was not the case in Alexandria. So all he needed was the length of the shadow at noon on the solstice in Alexandria to construe the angle between the two obelisks and the distance between the two cities.

9. Upvote everything Carl Sagan.

10. We lost this man way too early!

11. *Demon Haunted World* might be my favorite. He writes like you’re sitting next to him. To be a genius like him would be grand, but to also have the emotional intelligence he had to not only educate, but to be so empathetic in combatting pseudoscience…we need another Sagan and I know that’s just not in the cards. What a gift to humanity.

12. The “brains” part is where you lose some people

13. Such a simple explanation that covers it completely yet flat earthers just ignore this.

14. One question I have for this: how was the time measured in ancient times? A sun dial would sort of complicate that experiment wouldn’t it?

15. I’m a simple man. I see Carl Sagan, I upvote.

16. Ancient Egypt*

17. This is an amazing explanation.

    But if the Greeks could only be in one location at a time, how did they know the shadow was different in each location?

18. I miss Carl Sagan

19. More proof against flat earth theories

20. >All you need is sticks, eyes, feet and brains.

    3 out of 4 for the flat Earthers… so close!

21. I’ve always been fascinated by how ancient philosophers & mathematicians developed complex scientific models or technology that we would assume belongs in a later century.

    If I said that photovoltaic panels were invented in the late 19th century, and the first solar panel was installed in 1884 New York, people would be rushing to Google to confirm my claim. [Here’s a nice write-up.](https://www.smithsonianmag.com/sponsored/brief-history-solar-panels-180972006/)

22. The ‘ancient Greeks’ hav nothing to do with this.

23. So… I’m guessing they weren’t using sundials to tell the time… What were they using instead?

24. Where do they sell those last thing?

25. Key part was the brain.

26. Is there a link to the whole video?

27. I haven’t seen this video in a long time but I’ve quoted it as anecdotal evidence multiple times. glad I can save it. Big Thanks OP!!

28. Yeah flat earthers, FU

29. All the amazing data aside , why is he wearing that red turtleneck top/sweater in that heat?????????

30. This question has been ask since time itself

31. Flatearthers will argue it’s flat because they have eyes and brains as well.

    So, it’s not that obvious. At least to some ‘special’ people.

32. unfortunately, brains are hard to get in people who believe the earth is flat

33. Can somebody explain to me how they were able to accurately determine that they were measuring the shadows at the same time? I’ve always loved this story, but my brain can never get past this one detail.

34. I dont think its gonna sink in in those flat earth fuckos

35. I vividly remember watching this particular part of Cosmos as a kid and having my mind blown at how simple he explained it.

36. Hail Sagan

37. This doesn’t make sense because how would the Greek guy know the different lengths of the shadows at the extract same time of day, did they have an accurate way to tell time, so he could stand at each obelisk and measure the shadow?

38. A brain! You ask for to much sir!

39. Don’t forget the *zest* for experiment

40. I remember my teacher in like third grade teaching us about this.