Top 10 Ways to Know the Earth is Not Flat
(1) The Moon
Now that humanity knows quite positively that the Moon is not a piece of cheese or a playful god, the phenomena that accompany it (from its monthly cycles to lunar eclipses) are well-explained. It was quite a mystery to the ancient Greeks, though, and in their quest for knowledge, they came up with a few insightful observations that helped humanity figure out the shape of our planet.
Aristotle (who made quite a lot of observations about the spherical nature of the Earth) noticed that during lunar eclipses (when the Earths orbit places it directly between the Sun and the Moon, creating a shadow in the process), the shadow on the Moons surface is round. This shadow is the Earths, and its a great clue on the spherical shape of the Earth.
Since the earth is rotating (see the Foucault Pendulum experiment for a definite proof, if you are doubtful), the consistent oval-shadow it produces in each and every lunar eclipse proves that the earth is not only round but spherical absolutely, utterly, beyond a shadow of a doubt not flat.
Refer to the following image from Wikipedia for more details on what happens during a lunar eclipse:
Click for the Original
(2) Ships and the Horizon
If youve been next to a port lately, or just strolled down a beach and stared off vacantly into the horizon, you might have, perhaps, noticed a very interesting phenomenon: approaching ships do not just appear out of the horizon (like they should have if the world was flat), but rather emerge from beneath the sea.
But you say ships do not submerge and rise up again as they approach our view (except in Pirates of the Caribbean, but we are hereby assuming that was a fictitious movie). The reason ships appear as if they emerge from the waves is because the world is not flat: its round.
Imagine an ant walking along the surface of an orange, into your field of view. If you look at the orange head on, you will see the ants body slowly rising up from the horizon, because of the curvature of the Orange. If you would do that experiment with a long road, the effect would have changed: The ant would have slowly materialized into view, depending on how sharp your vision is.
(3) Varying Star Constellations
This observation was originally made by Aristotle (384-322 BCE), who declared the Earth was round judging from the
(4) Shadows and Sticks
If you stick a stick in the [sticky] ground, it will produce a shadow. The shadow moves as time passes (which is the principle for ancient Shadow Clocks). If the world had been flat, then two sticks in different locations would produce the same shadow:
But they dont. This is because the earth is round, and not flat:
Eratosthenes (276-194 BCE) used this principle to calculate the circumference of the Earth quite accurately. To see this demonstrated, refer to my experiment video about Eratosthenes and the circumference of the earth The Earths curvature is tasty!.
(5) Seeing Farther from Higher
Standing in a flat plateau, you look ahead of you towards the horizon. You strain your eyes, then take out your favorite binoculars and stare through them, as far as your eyes (with the help of the binocular lenses) can see.
Then, you climb up the closest tree the higher the better, just be careful not to drop those binoculars and break their lenses. You then look again, strain your eyes, stare through the binoculars out to the horizon.
The higher up you are the farther you will see. Usually, we tend to relate this to Earthly obstacles, like the fact we have houses or other trees obstructing our vision on the ground, and climbing upwards we have a clear view, but thats not the true reason. Even if you would have a completely clear plateau with no obstacles between you and the horizon, you would see much farther from greater height than you would on the ground.
This phenomena is caused by the curvature of the Earth as well, and would not happen if the Earth was flat:
(6) Ride a Plane
If youve ever taken a trip out of the country, specifically long-destination trips, you could notice two interesting facts about planes and the Earth:
Planes can travel in a relatively straight line a very long time and not fall off any edges. They can also, theoretically (and some do, though with stops along the way), circle the earth.
Correction (Courtesy of Klaynos, from scienceforums.net): Apparently, planes can circle the Earth without stopping!
If you look out the window on a trans-Atlantic flight, you can, most of the times, see the curvature of the earth in the horizon. The best view of the curvature used to be on the Concorde, but that planes long gone. I cant wait seeing the pictures from the new plane by Virgin Galactic the horizon should look absolutely curved, as it actually is from a distance.
(A picture of the curved horizon from a Concorde plane can be seen here).
(7) Look at Other Planets
The Earth is different from other planets, that much is true. After all, we have life, and we havent found any other planets with life (yet). However, there are certain characteristics all planets have, and it will be quite logical to assume that if all planets behave a certain way, or show certain characteristics specifically if those planets are in different places or were created under different circumstances our planet is the same.
In other words: If so many planets that were created in different locations and under different circumstances show the same property, its likely that our own planet has the same property as well. All of our observations show planets are spherical (and since we know how theyre created, its also obvious why they are taking this shape). Unless we have a very good reason to think otherwise (which we dont), our planet is very likely the same.
In 1610, Galileo Galilei observed the moons of Jupiter rotating around it (click here to see a beautiful video reconstruction of his observations). He described them as small planets orbiting a larger planet a description (and observation) that was very difficult for the church to accept as it followed a geocentric model where everything was supposed to revolve around the Earth. This observation also showed that the planets (Jupiter, Neptune, and later Venus was observed too) are all spherical, and all orbit the sun.
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