Love your new channel! Keep it up! One question though- you mentioned that gravity is weaker farther from the center of the earth when talking about the pendulum, but then in your gravity map, you mention that gravity is weaker when you are closer to the center.
Good question - the geoid is a bit tricky to talk about. @Antzen10 and @chrisray1567 had similar questions. Let’s imagine that the Earth was entirely made of water and not spinning at all. It WOULD be a perfect sphere because the water on the surface will “fall” until every place on the surface is equidistant from the center of mass and the surface itself is orthogonal to gravity at every point. If there was a bulge anywhere, that water would be “uphill” and spread out until there was no bulge. Ok, now we add spinning. This causes the equator to displace outward - now it’s further from the center of mass - gravity is weaker. But what if the water somehow had different densities - mass was unequally distributed throughout. (That’s what’s happening with the stuff Earth is made of!) Water that was above a patch of higher mass would experience greater gravity than expected for that point on the ellipsoid - that area of the surface would now effectively be “downhill.” Water would flow downhill - and the surface above that high density patch would rise until the gravity was the same at the surface of this bulge as all other points around it. You can see this happening with actual water in the ocean that sits over a giant mountain on the ocean floor - due to the increased gravity (the rock of submarine peak is denser than the water around it) it pulls more water to it and the surface of the ocean bulges upward. So the ellipsoid is caused by spinning, which changes gravity - but the geoid is CAUSED by differing gravity. When I say where gravity is stronger, the surface bulges out - I mean where higher densities are making gravity stronger than expected at a given point in the ellipsoid - the earth sorta bunches up. The geoid is actually the earth kind of “trying” to create a level surface relative to gravity it experiences! In every episode we debate how complex to get - and in this case, this was one rabbit hole that we decided not to go down :)
@@Howtown that helps a lot! One of the things about this channel I most appreciate is that you dig deeper into the ‘how do we know’ part of the answers that so often get glossed over on other media. Of course there is a balance to be struck, I get it, (but my two cents would be to err on slightly too much detail. 😊 ). Keep doing your thing & thanks again!
Wait, you've already had Cleo, Hank, and now Simone on your channel in the first month? Impressive connections you must have. Much more impressive than the algorithm taking this long to let me know you existed. Awesome video! I like the pacing, the info, and the presentation style. It's not everyday my ADHD-addled brain will sit through 14 minutes of things I (mostly) already know just because I enjoy the way it's shown. I look forward to whatever - and whoever - you bring to the table next!
It is very impressive; however, Joss is one of the founding members of Vox and Adam is a Science reporter from NPR. And both of them are incredible journalists and science communicators with storied resumes. They aren't exactly some random 1 month old YT channel, haha. It also wouldn't surprise me if the "famous internet science communicators" sphere of influence isn't exactly HUGE.
You explained this without making it complex ,and you were able to keep me curious throughout the video. You guys are fantastic storytellers. Thankyou. It is crazy that you two are perfectly situated to perform that experiment.
How are the bike lanes there? I know Bogotá had a big shift towards bike infrastructure under Peñalosa and his predecessors, and I'm curious if it's as good as the internet says.
@@cmasjoan7333 Some areas of the city are made really well to allow bikers to move around. U can find bike lanes from the 170 to the 100 (roughly 70 blocks) both in the Séptima and Novena avenues in the north, but this is also truth in the 26 avenue that has a lane that goes almost from the airport to Bogotá's centre and many other examples. I would say is as good as the internet make it seem but you have to beware of the insecurity and weather
@@cmasjoan7333 Also the last administration made an effort to have more bike lanes. But, yeah, compared to other cities and taking into account the sheer size of this city, they are pretty good. Always could be better, but they are good, I think.
Love the visuals! One thing: maybe hold for one more beat after an explainer animation finishes playing before cutting away. Like at 7:38, give a second to look at the different lengths before cutting to Adam.
I’ve been going back through and watching all of these howtown videos. You guys are fantastic! Pacing, communication, visualisations, enthusiasm for the content, research, I can’t fault it! Truly fantastic videos to watch for curious minds
I loved this video but I noticed that the official captions are off a lot of the time, so the automatically transcribed ones ended up being much more accurate. Maybe something to look into?
Hi, I just wanted to say I truly LOVE your first three videos and I just singed up to contribute on your Patreon. I think the incentives for creators have made it so that a lot explainer videos lately are extremely shallow, prioritize cool editing and storytelling over substance and a significant chunk of their run time are sponsors. I know it is hard to make it out there independentely so I can't blame people for relying on sponsors. But the substance is just not there either, there are no insights or interesting connections being made. These first three videos had excellent pacing, they were packed with insights and they are really making me think about stuff. What you present is broken down into manageable bits but you are not treating the audience like dummies. It is just great work really and we need more of it.
As someone with a degree in Geodesy, i love these kind of videos! Its so interesting as a subject that to me is baffling it gets so little coverage. GPS sure made it easy, but it has such a rich history as a science.
12:57 just a small correction (from someone whose worked on satellite orbit design before): The series that you showed on screen isn't an 'equation to describe the shape of the Earth precisely with ~200 terms'. It called a spherical harmonic expansion which is done as an approximation to any given shape. By tuning the coefficients (P, C and S), you can construct all kinds of shapes and given enough number of terms in the series these replications can be arbitrarily precise. The best estimate for Earth probably stops at 230 coefficients but in principle the shape of the Earth exactly described (with every building and blade of grass) would require infinite spherical harmonic terms
Perhaps I'm dumbing it down a bit but I'd still call that an equation! And while the World Geodetic System 1984 used coefficients up to degree and order 180 ... the current update uses coefficients up to degree 2190 and order 2159. So it seems the US Military thinks they are still getting better and better estimates of Earth's shape ...
@@Howtown Yep! You're right. The way its written on the screen, it is indeed an equation (with the summation symbols). But if you truncate it at some finite number of terms then the RHS would only approximately equal to the LHS (as opposed to being exactly equal, which is what an equation requires)
It varies because the planet is not perfectly spherical (some places are closer to the centre than others) or uniformly dense (lots of different types of rock but also water). In addition, gravity is weaker at the equator due to centrifugal forces produced by the planet’s rotation. It’s also weaker at higher altitudes, further from Earth’s centre, such as at the summit of Mount Everest. Mount Nevado Huascarán in Peru has the lowest gravitational acceleration, at 9.7639 m/s2, while the highest is at the surface of the Arctic Ocean, at 9.8337 m/s2.
It’s a bit paradoxical to me because it seems like being further from the center of the earth would means there’s more mass under you, and more mass would mean a stronger gravitational force, not less. I think the resolution to this paradox is that the strength of gravity is only linearly proportional to mass (doubling the mass doubles the gravitational force) while it is inversely proportional by the square of the distance (the gravitational force is four times weaker if you double the distance). In other words, while there is more mass under you, the increased distance has a greater effect (weakening it) on the total gravitational force you experience.
The force of gravity (minus centrifugal force) is the same at sea level everywhere on Earth. If that weren't true, the water in the oceans would flow from high to low until it were true. The thing that varies slightly from place to place is the distance between sea level and the center of the earth. This variation is due to Earth's rotation as well as variations in the density of rock.
@@chrisray1567 I don't know if I'm saying anything different than you here, but we can also think about gravitational attraction as "pivoting" around the center of mass. The Earth's center of mass is right in the middle (pretty much). When you're situated one of the bulgier points of the Earth, your center of mass is further away from Earth's center of mass
"Why is it so close to exactly 40k" The answer in this case is "because that's what we based the meter on", but otherwise it does raise the very interesting question of "why _do_ people care about these coincidences?" Why is it that we think we rolling two sixes with dice is much harder than to roll a 3 and a 4?
Quick note before watching, new thumbnail “how do they know the Earth circumference” is way better than old one. I do know that Earth is not a sphere, that doesn’t make to have a thought about clicking
the first homework we gave to my students back in 2020, was to measure the circumference of the earth. we were able to ask that of them because Chile is pretty much a straight line and because of the pandemic we had students from all over the country.
Hey, I think there's a typo in the subtitles at 2:42 it says "inside" and I'm guessing that it's supposed to be "in Syene"? Sorry if I'm mistaken but it seems like a typo. Love the video though! Edit: oh and at 4:17 it says "our city's" instead of "Eratosthenes"
At 10:30, I think you guys got the spectrum flipped; gravity is weaker at places where the surface bulges out and stronger at places where the surface sags. Awesome video and visualizations though, and I really enjoyed going through the different historical techniques!
The interesting thing about the estimated geoid equation is that it's specifically very accurate around the United States because they were the ones to come up with the formula. There are other equations that are slightly more accurate in other parts of the world, but because of the US's dominance with GPS mapping, the US-centric equation is what stuck.
Yes! And Sagan only took 6 minutes to explain what they here pad to almost 15 minutes (and I was more enthralled, entertained and dare I say educated by Sagan).
Is the 40,007.863 number an average based off that standardized ellipsoid? Or is it a measurement at a particular path, such as the prime meridian? Wouldn't you get slightly different numbers for polar circumference if you measure at different meridians?
40,007.863 km is the polar circumference of the reference ellipsoid, which was chosen to minimize the distance to the geoid around the entire globe (in 1984 - the geoid does change). That ellipsoid has the same polar circumference at every meridian. The geoid would have a slightly different circumference depending on which meridian you chose.
i really like how to scientist's punk rock band background relates to the invention of the meter. I thought you were just being generous in introducing him, and after that I kept wonderinf when is he going to show up again giving his opinion or lecture on the topic, why did you show him so early lol.
I wish you would have mentioned how Erastothanes synchronized the time of his observations, nontrivial for him. I assume he chose summer solstice solar max because solar max is easy to measure and is at the same time along longitude lines. Also would love to hear about error analysis, sounds boring but so crucial! How much variation can be detected in each measurement? How many decimal places are you accurate to?
Can you please do a video on how stampedes work? And how to save yourself if you are in one? Stampedes are scary and unpredictable and I believe its good to understand the well enough!!
Hi. Love the channel have been subbed since the first video. I want to see the channel succeed, and it is with that mindset I tell you I think it was a mistake making the original title/thumbnail about the earth not being a sphere. I understand perhaps you thought people would be intrigued by the idea, but you lost the pull of the original question the video seeks to answer: how do we know the circumference of the earth? It is questions like these that inspire the very existence of this channel - things we take for granted but don't actually know. The pull is not some other related question that we never asked ourselves before. Trust in the appeal of the simple, universal questions that everyone can understand. Don't lose sight of what makes this channel what it is. But hey, that's just my opinion 🤷🏻♂️❤
I noticed that you didn't mention Al-Biruni, who was a pioneer in this field. Around the 11th century, he developed a method that was incredibly accurate for its time. By measuring the height of a mountain and using trigonometry to observe the horizon, he calculated the Earth's circumference to within a small margin of error compared to today's measurements. His work is a great example of the advanced scientific thinking that was happening in the Islamic world long before many European scholars tackled similar problems."
Here's something to fact check. According to the British TV show "QI" and a few other sources, there's no evidence that humans in history thought the earth was flat. And that the flat earth theory is a recent thing.
Hmmm ... I know that Homer (from Greece, not Springfield) describes a shield that shows the whole world - and it definitely sounds like he's talking about a flat disc ... in other places he describes the sky as a dome. It does make sense to me that the default position -- before you start to really pay attention -- would be that the earth was flat (as one of the commenters on this video said it's "obviously flat"!). But I do know that the modern Flat Earth movement really got going in the 19th century.
At 7:28 you said since the equator is further from the center of the mass than the pole, it has weaker gravity. However, at 10:20 you also said when the earth bulges out, the gravity is stronger. Isn't this contradictory? @Howtown
Yep - it was a combination of some small errors (that forever tortured some of the meter’s creators - read “Measure of All Things” by Alder) and differences between the reference ellipse we now use and the ideal ellipse assumed in the 18th century
At 10:24, i dont seem to understand this map they show. To my limited logic it doesn't make sense how a region that is lower down (and therefore closer to the center of the earth) experiences less gravity than a place on the earth that "bulges out" and that is therefore farther away from the center.
I was also confused because the opposite would be true if you were above a black hole (gravity is inversely proportional to the square of distance). Farther away means less gravity. But in this case, the amount of mass is also changing. If you are lower down, there is less "stuff" beneath you (less mass), so you experience less gravity. If you are at a bulge, there is more earth and more gravity.
It seems to me that the distance would still have a larger effect overall seeing as it is squared. But is it that, because the volume (meters cubed) of earth changes beneath your feet whether you're lower down or higher up, that in fact the amount of earth pulling in meters cubed on you has a larger effect than the distance in meters squared between you and the center?
Love what you guys are doing. Maybe a dumb question, but does it matter that the angle of the shadows don't intersect at the center of the earth? The geometric construction srrmed rushed to me, or maybe im just slow.
Not dumb - we flew through that pretty fast. On a perfect sphere, if you extended a line straight down from the obelisks (or Pringles cans), those lines would meet at the center of the Earth. That’s the assumption we made, and Eratosthenes made. But since the Earth isn’t a perfect sphere, those lines wouldn’t quite meet at the center - introducing error into the calculation. Does that answer your Q?
@@Howtown Thank so much! That clarifies it for me. It could be an optical illusion from the crop/framing, but the intersection of the lines don't appear to me to be the center of the arc shown (at approx. 2:13 and 2:25). Maybe a dot at the center or a wider crop would help?
What I've always wanted to know: How did the ancient Greeks managed to figure out all of that trigonometry and geometry? What sort of instruments and thinking processes did they use?
somewhere the earth is exactly 40000km in circumference. The new number is just the average taken from the WGS 84 Ellipsoid. Also I'm almost certain the earth would also slightly change in size depending on temperature wouldn't it?
The whole "earth isn't a sphere" thing is a bit misleading. Nothing is a perfect sphere. The earth is pretty darn close to a sphere. Stating otherwise is a bit pedantic.
Love the videos. I wanted to watch your “flat earth” discussion that you mentioned, but found out the minimum Patreon donation is $8/month, which is the same as my Hulu subscription that gives me way more content. Don’t get me wrong, I like your stuff, and if I could pay 1-2 dollars a month for it, I’d consider it. But $8 isn’t in the budget for a TH-cam channel. Maybe reconsider your pricing?
The upshot is you could have shadows of the lengths we observed if the Earth was flat and the Sun was ~4,000 km (~2,500 mi) above the surface (closer to Adam than to Joss). On patreon.com/howtown we chat about a few ways you could modify the experiment to determine if this is what’s actually going on
If you want to learn way too much about the measurement of the kilometer, I suggest reading "The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World". If you want to keep your sanity, I suggest you don't 🤣It's ... lengthy.
Love your new channel! Keep it up! One question though- you mentioned that gravity is weaker farther from the center of the earth when talking about the pendulum, but then in your gravity map, you mention that gravity is weaker when you are closer to the center.
Good question - the geoid is a bit tricky to talk about. @Antzen10 and @chrisray1567 had similar questions. Let’s imagine that the Earth was entirely made of water and not spinning at all. It WOULD be a perfect sphere because the water on the surface will “fall” until every place on the surface is equidistant from the center of mass and the surface itself is orthogonal to gravity at every point. If there was a bulge anywhere, that water would be “uphill” and spread out until there was no bulge.
Ok, now we add spinning. This causes the equator to displace outward - now it’s further from the center of mass - gravity is weaker.
But what if the water somehow had different densities - mass was unequally distributed throughout. (That’s what’s happening with the stuff Earth is made of!) Water that was above a patch of higher mass would experience greater gravity than expected for that point on the ellipsoid - that area of the surface would now effectively be “downhill.” Water would flow downhill - and the surface above that high density patch would rise until the gravity was the same at the surface of this bulge as all other points around it. You can see this happening with actual water in the ocean that sits over a giant mountain on the ocean floor - due to the increased gravity (the rock of submarine peak is denser than the water around it) it pulls more water to it and the surface of the ocean bulges upward.
So the ellipsoid is caused by spinning, which changes gravity - but the geoid is CAUSED by differing gravity. When I say where gravity is stronger, the surface bulges out - I mean where higher densities are making gravity stronger than expected at a given point in the ellipsoid - the earth sorta bunches up. The geoid is actually the earth kind of “trying” to create a level surface relative to gravity it experiences!
In every episode we debate how complex to get - and in this case, this was one rabbit hole that we decided not to go down :)
@@Howtown that helps a lot! One of the things about this channel I most appreciate is that you dig deeper into the ‘how do we know’ part of the answers that so often get glossed over on other media. Of course there is a balance to be struck, I get it, (but my two cents would be to err on slightly too much detail. 😊 ). Keep doing your thing & thanks again!
That answer is incredible. I thought I'd caught a small error, turns out it was fully intentional and I got schooled
This explanation is exceptionally articulated! Well done 👏
@@Howtown I think this calls for its own patreon video.
Clicking this video and absolutely hyped to hear about those Greek dudes and their trigonometry
Egyptian not Greek
@AJ5 He was born in a Greek colony and lived and died as a citizen of Greece. Dude was Greek.
Better than the things I was taught in school
ABSOLUTELY MEEE
Wait, you've already had Cleo, Hank, and now Simone on your channel in the first month? Impressive connections you must have. Much more impressive than the algorithm taking this long to let me know you existed.
Awesome video! I like the pacing, the info, and the presentation style. It's not everyday my ADHD-addled brain will sit through 14 minutes of things I (mostly) already know just because I enjoy the way it's shown. I look forward to whatever - and whoever - you bring to the table next!
It is very impressive; however, Joss is one of the founding members of Vox and Adam is a Science reporter from NPR. And both of them are incredible journalists and science communicators with storied resumes. They aren't exactly some random 1 month old YT channel, haha.
It also wouldn't surprise me if the "famous internet science communicators" sphere of influence isn't exactly HUGE.
The research, the visuals and the explanation, absolutely wonderful! Brilliant!
Friend-shaped
drawfee moment
Beeg potato
bdg momento numero dos
You explained this without making it complex ,and you were able to keep me curious throughout the video. You guys are fantastic storytellers. Thankyou.
It is crazy that you two are perfectly situated to perform that experiment.
Imagine my surprise when I found out that you're living in my home city Bogotá, awesome experiment, awesome channel, subscribed from day 1
How are the bike lanes there? I know Bogotá had a big shift towards bike infrastructure under Peñalosa and his predecessors, and I'm curious if it's as good as the internet says.
@@cmasjoan7333 Some areas of the city are made really well to allow bikers to move around. U can find bike lanes from the 170 to the 100 (roughly 70 blocks) both in the Séptima and Novena avenues in the north, but this is also truth in the 26 avenue that has a lane that goes almost from the airport to Bogotá's centre and many other examples. I would say is as good as the internet make it seem but you have to beware of the insecurity and weather
@@cmasjoan7333 Also the last administration made an effort to have more bike lanes. But, yeah, compared to other cities and taking into account the sheer size of this city, they are pretty good. Always could be better, but they are good, I think.
As a GIS analyst I knew all this but you broke it down great and helped more people understand. Good stuff
Love the visuals! One thing: maybe hold for one more beat after an explainer animation finishes playing before cutting away. Like at 7:38, give a second to look at the different lengths before cutting to Adam.
Agree. Ty!
0:45 flat earthers got excited for a while
Super-impressed with the artful effects. The overlapping text to illustrate a face particularly caught my eye.
Noticed a thumbnail with Simone in my recommendations, watched, liked and subscribed. 👍👍
I’ve been going back through and watching all of these howtown videos. You guys are fantastic! Pacing, communication, visualisations, enthusiasm for the content, research, I can’t fault it! Truly fantastic videos to watch for curious minds
These animations, sound, writing...dang. Great explanations created with words and images
The visual effects in your videos are incredible!!
I loved this video but I noticed that the official captions are off a lot of the time, so the automatically transcribed ones ended up being much more accurate. Maybe something to look into?
Stumbled across this channel from shorts. Immediately subscribed 😁 Loving it, cant wait for more!
Hi, I just wanted to say I truly LOVE your first three videos and I just singed up to contribute on your Patreon. I think the incentives for creators have made it so that a lot explainer videos lately are extremely shallow, prioritize cool editing and storytelling over substance and a significant chunk of their run time are sponsors. I know it is hard to make it out there independentely so I can't blame people for relying on sponsors. But the substance is just not there either, there are no insights or interesting connections being made. These first three videos had excellent pacing, they were packed with insights and they are really making me think about stuff. What you present is broken down into manageable bits but you are not treating the audience like dummies. It is just great work really and we need more of it.
Thanks so much - I'm glad that's coming through because we're trying our best!
As someone with a degree in Geodesy, i love these kind of videos! Its so interesting as a subject that to me is baffling it gets so little coverage. GPS sure made it easy, but it has such a rich history as a science.
You and the other Vox alumni are keeping the Vox video heritage alive
12:57 just a small correction (from someone whose worked on satellite orbit design before): The series that you showed on screen isn't an 'equation to describe the shape of the Earth precisely with ~200 terms'. It called a spherical harmonic expansion which is done as an approximation to any given shape. By tuning the coefficients (P, C and S), you can construct all kinds of shapes and given enough number of terms in the series these replications can be arbitrarily precise. The best estimate for Earth probably stops at 230 coefficients but in principle the shape of the Earth exactly described (with every building and blade of grass) would require infinite spherical harmonic terms
Perhaps I'm dumbing it down a bit but I'd still call that an equation! And while the World Geodetic System 1984 used coefficients up to degree and order 180 ... the current update uses coefficients up to degree 2190 and order 2159. So it seems the US Military thinks they are still getting better and better estimates of Earth's shape ...
@@Howtown Yep! You're right. The way its written on the screen, it is indeed an equation (with the summation symbols). But if you truncate it at some finite number of terms then the RHS would only approximately equal to the LHS (as opposed to being exactly equal, which is what an equation requires)
10:29 cat cat cat cat cat cat cat cat cat
This channel is mindblowing!
You mentioned that gravity is weaker in some places and stronger in others. Why and how is this possible?
It varies because the planet is not perfectly spherical (some places are closer to the centre than others) or uniformly dense (lots of different types of rock but also water). In addition, gravity is weaker at the equator due to centrifugal forces produced by the planet’s rotation. It’s also weaker at higher altitudes, further from Earth’s centre, such as at the summit of Mount Everest.
Mount Nevado Huascarán in Peru has the lowest gravitational acceleration, at 9.7639 m/s2, while the highest is at the surface of the Arctic Ocean, at 9.8337 m/s2.
What Alexander said!
It’s a bit paradoxical to me because it seems like being further from the center of the earth would means there’s more mass under you, and more mass would mean a stronger gravitational force, not less.
I think the resolution to this paradox is that the strength of gravity is only linearly proportional to mass (doubling the mass doubles the gravitational force) while it is inversely proportional by the square of the distance (the gravitational force is four times weaker if you double the distance). In other words, while there is more mass under you, the increased distance has a greater effect (weakening it) on the total gravitational force you experience.
The force of gravity (minus centrifugal force) is the same at sea level everywhere on Earth. If that weren't true, the water in the oceans would flow from high to low until it were true. The thing that varies slightly from place to place is the distance between sea level and the center of the earth. This variation is due to Earth's rotation as well as variations in the density of rock.
@@chrisray1567 I don't know if I'm saying anything different than you here, but we can also think about gravitational attraction as "pivoting" around the center of mass. The Earth's center of mass is right in the middle (pretty much). When you're situated one of the bulgier points of the Earth, your center of mass is further away from Earth's center of mass
The analogies you guys make are just awesome!!! So gald I found this channel from the beginning. Sub since 1st video!!❤️
I have notifications one for this channel, and with this graphic 1:00 did not disappoint
This channel is so, so fantastic. Keep up the great work!
"Why is it so close to exactly 40k"
The answer in this case is "because that's what we based the meter on", but otherwise it does raise the very interesting question of "why _do_ people care about these coincidences?" Why is it that we think we rolling two sixes with dice is much harder than to roll a 3 and a 4?
Placing Eratosthenes in time was a good touch.
Boy, I hope this channel booms cause your content is fire 🔥
Quick note before watching, new thumbnail “how do they know the Earth circumference” is way better than old one. I do know that Earth is not a sphere, that doesn’t make to have a thought about clicking
I clicked because of Simone, disappointed that she's in the video for all of 9 seconds.
9 seconds of Simone garners trust more than a verified checkmark. 😂
Nods. I think adding a follow-up where the guest gets to remark on the explanation is better, like with Hank.
Trivia Q: what place on Earth’s surface is furthest from the center of the planet?
The Himalayas?
Must be a mountain along the equator due to the equatorial bulge?
Chimborazo! (A volcano in Ecuador.) Sí o no Adam?
@@briantorres6614🗻
How close would t 14:35 he sun have to be, for the calculations o of the experiment to match?
the first homework we gave to my students back in 2020, was to measure the circumference of the earth. we were able to ask that of them because Chile is pretty much a straight line and because of the pandemic we had students from all over the country.
I have absolutely been loving the content you all have been releasing. Keep it up!
Thanks Matt!
Hey, I think there's a typo in the subtitles at 2:42 it says "inside" and I'm guessing that it's supposed to be "in Syene"? Sorry if I'm mistaken but it seems like a typo. Love the video though!
Edit: oh and at 4:17 it says "our city's" instead of "Eratosthenes"
Thanks! Loved this episode!
New Howtown video?? It’s for sure gonna be a good day now
I knew parts of the story, but I was not expecting to learn so many fascinating new details in this video
Great one! Keep the videos coming.
At 10:30, I think you guys got the spectrum flipped; gravity is weaker at places where the surface bulges out and stronger at places where the surface sags.
Awesome video and visualizations though, and I really enjoyed going through the different historical techniques!
The interesting thing about the estimated geoid equation is that it's specifically very accurate around the United States because they were the ones to come up with the formula. There are other equations that are slightly more accurate in other parts of the world, but because of the US's dominance with GPS mapping, the US-centric equation is what stuck.
This was more interesting than I expected! I had no idea that the Earth was so lumpy.
This was so much fun to watch and so interesting and my brain is kinda melted
Wait, so Adam Cole was always in Bogotá? I'll love to meet you someday, this channel is so great
Best channel on this site.
I learned about Eratosthenes' work on measuring the Earth's circumference from Carl Sagan in the original Cosmos.
Yes! And Sagan only took 6 minutes to explain what they here pad to almost 15 minutes (and I was more enthralled, entertained and dare I say educated by Sagan).
Is the 40,007.863 number an average based off that standardized ellipsoid? Or is it a measurement at a particular path, such as the prime meridian? Wouldn't you get slightly different numbers for polar circumference if you measure at different meridians?
40,007.863 km is the polar circumference of the reference ellipsoid, which was chosen to minimize the distance to the geoid around the entire globe (in 1984 - the geoid does change). That ellipsoid has the same polar circumference at every meridian. The geoid would have a slightly different circumference depending on which meridian you chose.
My brain hearing hbomberguy say "oblate"
How do they know which plants are native and which ones are invasive?
Does the argument of earth’s shape includes the water of our oceans?
i really like how to scientist's punk rock band background relates to the invention of the meter. I thought you were just being generous in introducing him, and after that I kept wonderinf when is he going to show up again giving his opinion or lecture on the topic, why did you show him so early lol.
I wish you would have mentioned how Erastothanes synchronized the time of his observations, nontrivial for him. I assume he chose summer solstice solar max because solar max is easy to measure and is at the same time along longitude lines.
Also would love to hear about error analysis, sounds boring but so crucial! How much variation can be detected in each measurement? How many decimal places are you accurate to?
Hooray! Simone is the best!!
Can you please do a video on how stampedes work? And how to save yourself if you are in one?
Stampedes are scary and unpredictable and I believe its good to understand the well enough!!
The title is going to excite flat-earthers. “If only they had a brain”
So cool! I love that the math makes sense the way you explain it, thank you!
Hi. Love the channel have been subbed since the first video.
I want to see the channel succeed, and it is with that mindset I tell you I think it was a mistake making the original title/thumbnail about the earth not being a sphere.
I understand perhaps you thought people would be intrigued by the idea, but you lost the pull of the original question the video seeks to answer: how do we know the circumference of the earth? It is questions like these that inspire the very existence of this channel - things we take for granted but don't actually know. The pull is not some other related question that we never asked ourselves before.
Trust in the appeal of the simple, universal questions that everyone can understand. Don't lose sight of what makes this channel what it is.
But hey, that's just my opinion 🤷🏻♂️❤
Fantastic content!
A bit late to the party, but how did Eratosthenes determine noon time in the two cities?
I noticed that you didn't mention Al-Biruni, who was a pioneer in this field. Around the 11th century, he developed a method that was incredibly accurate for its time. By measuring the height of a mountain and using trigonometry to observe the horizon, he calculated the Earth's circumference to within a small margin of error compared to today's measurements. His work is a great example of the advanced scientific thinking that was happening in the Islamic world long before many European scholars tackled similar problems."
This channel is impressing me
Waitt what how did I not know about the website that's so cool
BRB training to become a bematist - Y'ALL this is SO good!
Really well made! Love it
Here's something to fact check.
According to the British TV show "QI" and a few other sources, there's no evidence that humans in history thought the earth was flat.
And that the flat earth theory is a recent thing.
Hmmm ... I know that Homer (from Greece, not Springfield) describes a shield that shows the whole world - and it definitely sounds like he's talking about a flat disc ... in other places he describes the sky as a dome. It does make sense to me that the default position -- before you start to really pay attention -- would be that the earth was flat (as one of the commenters on this video said it's "obviously flat"!). But I do know that the modern Flat Earth movement really got going in the 19th century.
Love this!
I want a video like this to explain every question I have lol
At 7:28 you said since the equator is further from the center of the mass than the pole, it has weaker gravity. However, at 10:20 you also said when the earth bulges out, the gravity is stronger. Isn't this contradictory? @Howtown
I have heard his voice before but on which channel. Anyone has any idea!
Subscribed!
No credits for the Jean Riché voice actor?!
Great Video!
I don't remember where I heard this but I thought the extra few kilometers was caused by a miscalculation
Yep - it was a combination of some small errors (that forever tortured some of the meter’s creators - read “Measure of All Things” by Alder) and differences between the reference ellipse we now use and the ideal ellipse assumed in the 18th century
At 10:24, i dont seem to understand this map they show. To my limited logic it doesn't make sense how a region that is lower down (and therefore closer to the center of the earth) experiences less gravity than a place on the earth that "bulges out" and that is therefore farther away from the center.
I was also confused because the opposite would be true if you were above a black hole (gravity is inversely proportional to the square of distance). Farther away means less gravity.
But in this case, the amount of mass is also changing. If you are lower down, there is less "stuff" beneath you (less mass), so you experience less gravity. If you are at a bulge, there is more earth and more gravity.
It seems to me that the distance would still have a larger effect overall seeing as it is squared. But is it that, because the volume (meters cubed) of earth changes beneath your feet whether you're lower down or higher up, that in fact the amount of earth pulling in meters cubed on you has a larger effect than the distance in meters squared between you and the center?
@@thurian7144 That's right, the volume (r^3) has a greater effect than distance (r^2).
@@qr6QRbMBG6hjGpZhnWqG Noted, Thank you very much for your help
I see a video about maps & satellite images, I click
Love what you guys are doing. Maybe a dumb question, but does it matter that the angle of the shadows don't intersect at the center of the earth? The geometric construction srrmed rushed to me, or maybe im just slow.
Not dumb - we flew through that pretty fast. On a perfect sphere, if you extended a line straight down from the obelisks (or Pringles cans), those lines would meet at the center of the Earth. That’s the assumption we made, and Eratosthenes made. But since the Earth isn’t a perfect sphere, those lines wouldn’t quite meet at the center - introducing error into the calculation. Does that answer your Q?
@@Howtown Thank so much! That clarifies it for me. It could be an optical illusion from the crop/framing, but the intersection of the lines don't appear to me to be the center of the arc shown (at approx. 2:13 and 2:25). Maybe a dot at the center or a wider crop would help?
They used a really long measuring tape.
What is the difference between the polar circumference and the equatorial circumference?
67.154 km (41.728 miles)
New Favorite channel
Brilliant 🎉
I’m assuming they knew they had a north south relationship because of the stars. Is that correct?
What I've always wanted to know: How did the ancient Greeks managed to figure out all of that trigonometry and geometry? What sort of instruments and thinking processes did they use?
JOSS IS LIFEEEEE
wait, Simone Giertz and Cadamole? what channel IS THIS?
More howtown!
actually simplified of ny 3 yrs bachelor degrees of geodesy 😁 am happy to recall
6:31 Bro I got fucking scared that Newton was moving eeriely realistically. How????
displacement maps
What about water? The geoid doesnt include water right?
somewhere the earth is exactly 40000km in circumference. The new number is just the average taken from the WGS 84 Ellipsoid. Also I'm almost certain the earth would also slightly change in size depending on temperature wouldn't it?
The whole "earth isn't a sphere" thing is a bit misleading. Nothing is a perfect sphere. The earth is pretty darn close to a sphere. Stating otherwise is a bit pedantic.
It's an oblate spheroid
Love the videos. I wanted to watch your “flat earth” discussion that you mentioned, but found out the minimum Patreon donation is $8/month, which is the same as my Hulu subscription that gives me way more content. Don’t get me wrong, I like your stuff, and if I could pay 1-2 dollars a month for it, I’d consider it. But $8 isn’t in the budget for a TH-cam channel. Maybe reconsider your pricing?
curious how the experiment would work, if the earth was flat.
nice cliffhanger 🤓
The upshot is you could have shadows of the lengths we observed if the Earth was flat and the Sun was ~4,000 km (~2,500 mi) above the surface (closer to Adam than to Joss). On patreon.com/howtown we chat about a few ways you could modify the experiment to determine if this is what’s actually going on
Amazing
If you want to learn way too much about the measurement of the kilometer, I suggest reading "The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World". If you want to keep your sanity, I suggest you don't 🤣It's ... lengthy.
the ADR is strong in this one
Neat!
I hope you talked to Johnny H before you did a map related video
Eratosthenes is smarter than all the flat earthers out there 😂
Well, to be fair, it is not that hard to be smarter than all the flatties together since they are all inexplicably uneducated and ignorant.
why is Simon here? answer! answer!