We Got The Radius Of The Earth!

With the help of 70 people from around the world we got the radius of the Earth. There was a better turnout than I could have hoped for. Sorry for the delay, it took a while to edit this one together.
The first video:
Check out thunderf00t's channel for some other good science education videos:

[magustx]

this is so awesome! Applying math and science to the real world is such a good way to teach!

[ThePolyAtheist]

YES! I'm so glad to have helped, I knew being this much far south would prove useful for this particular experiment! Greetings from Argentina, everyone!

[SpottedSharks]

you can demonstrate earth's radius by using the formula to compute the distance between two points on a sphere. only works on a sphere.

[TheGentlemanPhysicis]

That's also a problem with editing videos at 3AM, my jokes aren't nearly as funny as they sound in my head.

[ThePolyAtheist]

I was lucky enough to get a sunny day, albeit a day later (I'm part of that 'late entry')... That's the way of the winter! Anyway, now I feel proud when I bump on my chest and shout "Science, bitches! It works!"

And John (TheGentlemanPhysicist), thank you for letting many of us to be part of this! Your success is our success now, and you are a true Gentleman.

[Gripfang]

Yay!
Thanks for coming up with such a neat project for us to participate in.
My dad(a retired college math teacher) will get a kick out of seeing the results of our collaborative work.

[TheGentlemanPhysicis]

That could work, but I'm not sure how accurate it would be. There would still be some errors on the distances. That could cause a pretty big error in the measurement of the radius. Although it is a fun excuse to rent sailboat.

[AWWx]

Well engineered experiment and excellently produced summary of your experiment! So happy to see the results. Love your videos. You rock!

[TheGentlemanPhysicis]

You are right that there are many different ways of doing more complicated analyses, but one of the challenges of these videos is to keep the math as simple as possible without compromising the physics. If that means a first order approximation then that's the approach I take. :)

[TheGentlemanPhysicis]

Thanks for trying to participate, it's a shame about the weather. Unfortunately the database has some people's personal data in it and I just don't have the time to go through it all to make sure it's gone :(.
Sorry
J

[energyquicksand]

Sorry to be so late in looking up the results of the project but glad to have participated. Great fun and interesting.

[mythousandfaces]

Who's my countryperson from Malta who took part?

[apopalz]

Jim Khalil replicated Al Beruni method (at a different location to Pakistan) and found circumference at 1%. Another fantastic use of astrolabe and trigonometry.

[TheGentlemanPhysicis]

Glad you liked it, got a way better turn out than I could of hoped :)

[mindbomb]

Were these data points all taken at the same time, at local solar noon? I don't quite understand.

[LFTRnow]

Interesting, but I think the key difference is how much better we measure distances today. 16% is amazing when using time by camel as your measuring unit (if thats really how it was done). As I watched your video, I thought - how would they have measured large distances accurately back then?

[TheGentlemanPhysicis]

In reality the library was built centuries after Eratosthenes time. One of the biggest tragedies of the ancient world. :(

[TheGentlemanPhysicis]

I had the same problem one of the days, I was really worried it would be too overcast to take a time lapse video.

[hedleypanama]

Have you calculated a regression model of the latitude = angle. I know it was not the intention...

[gvitellozzi]

Can you post the protocol? At what time did the shadows were measured? OR did that matter at all?