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Ask a NASA astronomer! Is there proof that the Earth is round?

We've known for 2,000 years that the Earth is round. Here are three observable proofs that can instantly debunk flat-Earth theory.

Michelle Thaller: So, Oscar, you asked the question, “What are some of the easiest ways that you can prove that the Earth is round?” Because apparently, this is something that we’re debating—I have no idea why.

That’s a hard thing for me to even start talking about because there are so many proofs that the Earth is round, it’s difficult to know where to start. And it’s not okay to think that the Earth is flat. This is not a viable argument.

I have friends who have been on the International Space Station, they have orbited the Earth once every 90 minutes; I've had personal experience with people who have been up in space and can see with their own eyes that the Earth is round. And of course, we‘ve taken all of these amazing pictures from space; they’re so beautiful, all those pictures of the Earth.

So I don’t really know what’s going on right now with this 'Earth is flat' thing, but I will tell you that this is one of the things I really enjoyed teaching my own astronomy class about because there are proofs all around you. It is not difficult to know that the Earth is round. In fact, people have known of this for way more than 2,000 years. The ancient Greeks actually had a number of really elegant, wonderful proofs that the earth was a sphere. 

So let’s start from the simple to the slightly more complicated. One of the things you can see yourself, with a pair of binoculars, is if you actually go out to a lake and there are boats on that lake, the farther away a boat is the more the bottom of the boat will disappear, and you’ll basically just see the mast of the boat. And as a boat goes farther and farther away the last thing you will see is the very top of the mast of that boat, and that’s because the boat is actually going over the horizon that’s curved—and that means that as it goes farther and farther away you see less and less of the bottom of it, and more of the top of that. You can see that with binoculars by an ocean, by a lake, it’s really easy. That wouldn’t happen if the Earth were flat—you would simply see the boat getting smaller and smaller and smaller as it went farther away, but you’d be able to see the whole thing with the same proportions.

Now, another way that you can tell that we’re on a sphere is to think about how there’s something called the tropics on the Earth, and the tropics are places near the equator of the earth were sometimes the sun is overhead in the sky. This was actually something that the Greeks used, not only to prove that the Earth was round about 2000 years ago, but they actually measured the circumference of the Earth, accurate to within just a couple percent. 2,000 years ago we’ve known that the Earth was round.

There was a really brilliant Greek scientist called Eratosthenes, and Eratosthenes noticed that there was a town called Syene, and on a certain date the sun would actually shine straight down to the bottom of a well. That meant the sun was directly overhead; you could look down a well and see the sun shining back at you.

And on the very same date, farther away in the city of Alexandria, that didn’t happen. The sun was not directly overhead, it was a slight angle, and all that Eratosthenes did was he measured the difference in the angle of the sun. It was straight overhead in Syene; in Alexandria it was a little bit less than overhead, and he rationed that that change in angle from one city to another was probably indicative of us being on a curved surface, and you could make all kinds of measurements even between those two cities and see that the angles were different—the sun was at a different place in the sky. Using this, he actually measured the circumference of the Earth, and he got it right 2,000 years ago.

So another really simple proof is that on any given date, at different cities and different places around the world, the sun is at different angles in the sky. That wouldn’t happen if the Earth wasn’t round.

Then there are some other proofs that are a little more obscure, but they’re actually really lovely. One is to observe what happens during a lunar eclipse. Now, a lunar eclipse happens when the Earth casts a shadow on the moon. The moon actually goes dark, in fact, if you’ve seen one you can actually see the Earth’s shadow go across the moon, and when the moon is entirely in the Earth’s shadow the moon looks kind of dark and even kind of red-colored; it’s really, really beautiful.

What’s happening, in that case, is that the sun is on one side of the Earth—the Earth is in the middle—and the Earth is casting a shadow on the moon, and as the shadow moves across the moon you’ll notice that the shadow is curved, it’s round.

And so something like the sun that’s bigger than the Earth and is able to cast a shadow of the Earth on the moon can actually show you the shape of the Earth. “Ah-ha!” you might say, “but could the Earth to be a disk? Could it be flat but it’s actually still shaped like a disk, not like a sphere?”

There was a Greek scientist called Aristarchus and what he noticed was that you can get a lunar eclipse at many different angles where the sun is; sometimes the shadow goes straight across the moon, sometimes it just kind of glances the moon—just a little bit is in shadow just on the top or on the bottom. From every different vantage point, every different angle the sun is casting a shadow, you always get a perfectly curved shadow. The only shape that can cast a shadow that’s curved from any direction you put the light is a sphere.

So people have known that the Earth is spherical for thousands of years. It’s not okay to say that the Earth is flat. This is some sort of strange denial, I don’t know where it comes from, and it’s something where I keep getting this question. We really need to put this question to bed because we’ve known the Earth is a sphere for a long time.

There’s even some well-meaning people who say, “I don’t really believe the Earth is flat, but I’m not really sure what to think about it.” And they’ve asked me some interesting questions, like they’ve heard that space is a very hot, that when you go up above the atmosphere the temperature of space is millions of degrees, which is true. The problem is there’s basically no air at all. So the gas right around the Earth is actually millions of degrees hot. That’s actually true, but there’s almost none of it, there’s almost nothing. Like one single proton whizzes by you at a temperature of a million degrees, it’s not the same as temperature in the air, it’s not the same thing at all. So that's one that I get sometimes.

 

And the other one is—I actually said this to somebody, and I couldn’t believe they had never thought of it—that with binoculars you can see planets, you can see Saturn and Jupiter, you can see Mars with a telescope, the sun and the moon, everything else you see in the solar system is a sphere. So we’re the one thing that is different? And that actually made somebody who was more interested in actually hearing information, that actually got them to think. They were like, “You’re right… everything else we take a picture of is a sphere!”

Hey flat Earthers, it's time to put your theory to bed once and for all! A curious stargazer by the name of Oscar has submitted a question to Big Think's 'Ask an astronomer' series with NASA's Michelle Thaller. Oscar wants to know: "What would be the easiest proof that the Earth isn’t flat, that I could come back with whenever I get challenged on this issue?" Thaller sets the record straight. "There are so many proofs that the Earth is round, it’s difficult to know where to start. And it’s not okay to think that the Earth is flat; this is not a viable argument," she says. The ancient Greeks figured out we were living on a sphere over 2,000 years ago, and there are things you can do to prove that the Earth is indeed round—just go to a body of water and look at ships or boats on the horizon with binoculars. Thaller explains three observable proofs that instantly debunk flat-Earth theory with irrefutable evidence of the Earth's round, curvaceous, gloriously spherical shape. You can follow Michelle Thaller on Twitter at @mlthaller.


Radical innovation: Unlocking the future of human invention

Ready to see the future? Nanotronics CEO Matthew Putman talks innovation and the solutions that are right under our noses.

Big Think LIVE

Innovation in manufacturing has crawled since the 1950s. That's about to speed up.

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Quantum particles timed as they tunnel through a solid

A clever new study definitively measures how long it takes for quantum particles to pass through a barrier.

Image source: carlos castilla/Shutterstock
  • Quantum particles can tunnel through seemingly impassable barriers, popping up on the other side.
  • Quantum tunneling is not a new discovery, but there's a lot that's unknown about it.
  • By super-cooling rubidium particles, researchers use their spinning as a magnetic timer.

When it comes to weird behavior, there's nothing quite like the quantum world. On top of that world-class head scratcher entanglement, there's also quantum tunneling — the mysterious process in which particles somehow find their way through what should be impenetrable barriers.

Exactly why or even how quantum tunneling happens is unknown: Do particles just pop over to the other side instantaneously in the same way entangled particles interact? Or do they progressively tunnel through? Previous research has been conflicting.

That quantum tunneling occurs has not been a matter of debate since it was discovered in the 1920s. When IBM famously wrote their name on a nickel substrate using 35 xenon atoms, they used a scanning tunneling microscope to see what they were doing. And tunnel diodes are fast-switching semiconductors that derive their negative resistance from quantum tunneling.

Nonetheless, "Quantum tunneling is one of the most puzzling of quantum phenomena," says Aephraim Steinberg of the Quantum Information Science Program at Canadian Institute for Advanced Research in Toronto to Live Science. Speaking with Scientific American he explains, "It's as though the particle dug a tunnel under the hill and appeared on the other."

Steinberg is a co-author of a study just published in the journal Nature that presents a series of clever experiments that allowed researchers to measure the amount of time it takes tunneling particles to find their way through a barrier. "And it is fantastic that we're now able to actually study it in this way."

Frozen rubidium atoms

Image source: Viktoriia Debopre/Shutterstock/Big Think

One of the difficulties in ascertaining the time it takes for tunneling to occur is knowing precisely when it's begun and when it's finished. The authors of the new study solved this by devising a system based on particles' precession.

Subatomic particles all have magnetic qualities, and they spin, or "precess," like a top when they encounter an external magnetic field. With this in mind, the authors of the study decided to construct a barrier with a magnetic field, causing any particles passing through it to precess as they did so. They wouldn't precess before entering the field or after, so by observing and timing the duration of the particles' precession, the researchers could definitively identify the length of time it took them to tunnel through the barrier.

To construct their barrier, the scientists cooled about 8,000 rubidium atoms to a billionth of a degree above absolute zero. In this state, they form a Bose-Einstein condensate, AKA the fifth-known form of matter. When in this state, atoms slow down and can be clumped together rather than flying around independently at high speeds. (We've written before about a Bose-Einstein experiment in space.)

Using a laser, the researchers pusehd about 2,000 rubidium atoms together in a barrier about 1.3 micrometers thick, endowing it with a pseudo-magnetic field. Compared to a single rubidium atom, this is a very thick wall, comparable to a half a mile deep if you yourself were a foot thick.

With the wall prepared, a second laser nudged individual rubidium atoms toward it. Most of the atoms simply bounced off the barrier, but about 3% of them went right through as hoped. Precise measurement of their precession produced the result: It took them 0.61 milliseconds to get through.

Reactions to the study

Scientists not involved in the research find its results compelling.

"This is a beautiful experiment," according to Igor Litvinyuk of Griffith University in Australia. "Just to do it is a heroic effort." Drew Alton of Augustana University, in South Dakota tells Live Science, "The experiment is a breathtaking technical achievement."

What makes the researchers' results so exceptional is their unambiguity. Says Chad Orzel at Union College in New York, "Their experiment is ingeniously constructed to make it difficult to interpret as anything other than what they say." He calls the research, "one of the best examples you'll see of a thought experiment made real." Litvinyuk agrees: "I see no holes in this."

As for the researchers themselves, enhancements to their experimental apparatus are underway to help them learn more. "We're working on a new measurement where we make the barrier thicker," Steinberg said. In addition, there's also the interesting question of whether or not that 0.61-millisecond trip occurs at a steady rate: "It will be very interesting to see if the atoms' speed is constant or not."

Self-driving cars to race for $1.5 million at Indianapolis Motor Speedway ​

So far, 30 student teams have entered the Indy Autonomous Challenge, scheduled for October 2021.

Indy Autonomous Challenge
Technology & Innovation
  • The Indy Autonomous Challenge will task student teams with developing self-driving software for race cars.
  • The competition requires cars to complete 20 laps within 25 minutes, meaning cars would need to average about 110 mph.
  • The organizers say they hope to advance the field of driverless cars and "inspire the next generation of STEM talent."
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Bubonic plague case reported in China

Health officials in China reported that a man was infected with bubonic plague, the infectious disease that caused the Black Death.

(Photo by Centers for Disease Control and Prevention/Getty Images)
Coronavirus
  • The case was reported in the city of Bayannur, which has issued a level-three plague prevention warning.
  • Modern antibiotics can effectively treat bubonic plague, which spreads mainly by fleas.
  • Chinese health officials are also monitoring a newly discovered type of swine flu that has the potential to develop into a pandemic virus.
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The dangers of the chemical imbalance theory of depression

A new Harvard study finds that the language you use affects patient outcome.

Image: solarseven / Shutterstock
Mind & Brain
  • A study at Harvard's McLean Hospital claims that using the language of chemical imbalances worsens patient outcomes.
  • Though psychiatry has largely abandoned DSM categories, professor Joseph E Davis writes that the field continues to strive for a "brain-based diagnostic system."
  • Chemical explanations of mental health appear to benefit pharmaceutical companies far more than patients.
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