Because if the earth was truly falt and that we are going upward we would have collided with another planet by now...and also why havnt Aeroplanes been there...if the earth was truly flat someone would have been there by now...and the reason we dont fall off is because there is a little thing called GRAVITY!
here is more proof
Now that we have access to space, the easiest way to prove the Earth is spherical is to leave it and view it from a distance. Astronauts and space probes have done just that. Every picture of Earth ever taken shows only a circular shape, and the only geometric solid which looks like a circle from any direction is a sphere.
One of the oldest proofs of the Earth's shape, however, can be seen from the ground and occurs during every lunar eclipse. The geometry of a lunar eclipse has been known since ancient Greece. When a full Moon occurs in the plane of Earth's orbit, the Moon slowly moves through Earth's shadow. Every time that shadow is seen, its edge is round. Once again, the only solid that always projects a round shadow is a sphere.
Answered by: Paul Walorski, B.A., Part-time Physics/Astronomy Instructor
This is a question that has been asked for many years, and there are some very intuitive, and some not-so-intuitive answers.
To start with... there's a horizon, meaning that the surface that one is observing from is not an infinite plane. On the clearest of days, the only restriction to one's range of sight is the horizon. There can be two explanations for this - one, that the Earth at some point just stops, as if you were looking off the edge of a table. The other is that the Earth is round. Hundreds of years ago, before the invention of the compass or sextant, precise navigation for ships was difficult, even with the stars. Ships that ventured past sight of land were often lost, and thus it was generally believed that the world simply *stopped* at the end of the horizon. With the invention of the compass, and improved map-making, people began to dare more, and with the return of Columbus from his trans-Atlantic voyage, the concept of the Earth as flat was shattered.
Further proof of the Earth being round came after the voyage of Columbus. When Newton discovered and measured the force of gravity, that number could then be tested anywhere the theory was known. Since the force of gravity is roughly the same everywhere on the globe, it could be surmised that the Earth must be spherical. If the Earth were not round, whole hemispheres would have different atmospheric pressure and significantly different sea levels. Also, pictures taken of the Earth in the last 50 years have proved absolutely conclusively that the Earth is round. These are just the arguments that don't require much physics knowledge to explain, there are others that are more technical, but I think that the simplest arguments are the best.
Answered by: Frank DiBonaventuro, B.S., Physics grad, The Citadel, Air Force officer
There are a multitude of methods in which any one can prove that the earth is a sphere. These are the most common.
You can launch a rocket to a high altitude and take pictures of the earth (which various government agencies and private groups have already done thousands of times in the past), but that isn't the most practical way. Pictures and videos taken by orbiting satellites and space stations are certainly the most definitive proof that the earth is a sphere.
But if you're not convinced, read on...
You can also observe, with binoculars, ships slowly 'sinking' below the horizon as it sails farther and farther out to the ocean, then watch them come back. They certainly didn't fall off the edge of the earth! You can also sail or fly around the world.
The Greeks discovered that the earth is round by observing lunar eclipses (i.e. when the earth blocks the sun from the moon, casting its round shadow on the moon's surface).
Another method is simultaneously measuring the length of the shadows cast by identical poles perpendicular to a flat surface that is tangential to the earth's radius at various, distant locations. If indeed the earth is round, then the shadows should all vary in length from one distant location to another, which means that the angle at which the parallel rays of sunlight struck each pole varied from one location to another. (recall the alternate-angles theorem from Geometry class) If the earth is flat, then the lengths of all the shadows should be identical when measured simultaneously, since all rays of sunlight that strike the earth are parallel. However, they are not identical, but in fact, varies in such a way that the angles indicate a spherical surface. (This was one of the earliest methods to determine the radius of the earth)
Also, keep in mind the 24 hour time zones. When it is noon in Hawaii, it is approximately midnight in the Middle East and vice versa. How can it be noon and midnight simultaneously? It is certainly impossible with a flat earth and a sun millions of times more massive.
If I were a billionaire and physically fit, then proving to you the earth is round would be no problem. I can just take you with me on the space shuttle and we'll watch with our own eyes the earth from the orbiting International Space Station.
I have heard from astronauts that there is no experience comparable as watching the earth from above.
Today it is well known that the Earth is a sphere, or very close to one (its equator bulges out a bit because of the Earth's rotation). When Christopher Columbus proposed to reach India by sailing west from Spain, he too knew that the Earth was round. India was the source of precious spices and other rare goods, but reaching it by sailing east was difficult, because Africa blocked the way. On a round globe, however, it should also be possible to reach India by sailing west, and this Columbus proposed to do (he wasn't the first one to suggest this--see below).
Sometimes the claim is made that those who opposed Columbus thought the Earth was flat, but that wasn't the case at all. Even in ancient times sailors knew that the Earth was round and scientists not only suspected it was a sphere, but even estimated its size.
[IMAGE:What causes horizon]
If you stand on the seashore and watch a ship sailing away, it will gradually disappear from view. But the reason cannot be the distance: if a hill or tower are nearby, and you climb to the top after the ship has completely disappeared, it becomes visible again. Furthermore, if on the shore you watch carefully the way the ship disappears from view, you will notice that the hull vanishes first, while the masts and sails (or the bridge and smokestack) disappear last. It is as if the ship was dropping behind a hill, which in a way is exactly the case, the "hill" being the curve of the Earth's surface.
To find out how the distance to the horizon is calculated, click here
Eratosthenes, Posidonius and El Mamun
The Greek philosopher Aristotle (384-322 BC) argued in his writings that the Earth was spherical, because of the circular shadow it cast on the Moon, during a lunar eclipse. Another reason was that some stars visible from Egypt are not seen further north The full quotation can be found here.
The Alexandria philosopher Eratosthenes went one step further and actually estimated how large the Earth was. He was told that on midsummer day (June 21) in the town of Syene in southern Egypt (today Aswan, near a huge dam on the river Nile) the noontime Sun was reflected in a deep well, meaning that it was right overhead, at zenith. Eratosthenes himself lived in Alexandria, near the river's mouth, north of Syene, about 5000 stadia north of Syene (the stadium, the size of a sports arena, was a unit of distance used by the Greeks). In Alexandria the Sun on the corresponding date did not quite reach zenith, and vertical objects still threw a short shadow. Eratosthenes established that the direction of the noon Sun differed from the zenith by an angle that was 1/50 of the circle, that is, 7. 2 degrees, and from that he estimated the circumference of the Earth to be 250,000 stadia.
Tidbit: Eratosthenes also headed the royal library in Alexandria, the greatest and most famous library in classical antiquity. Officially it was called "temple of the muses" or "museion," from which our modern "museum" is derived.
Other estimates of the size of the Earth followed. Some writers reported that the Greek Posidonius used the greatest height of the bright star Canopus above the horizon, as seen from Egypt and from the island of Rhodes further north (near the southwestern tip of Turkey). He obtained a similar value, a bit smaller. The Arab Khalif El Ma'mun, who ruled in Baghdad from 813 to 833, sent out two teams of surveyors to measure a north-south baseline and from it also obtained the radius of the Earth. Compared to the value known today, those estimates were pretty close to the mark.
The idea of sailing westward to India dates back to the early Romans. According to Dr. Irene Fischer, who studied this subject, the Roman writer Strabo, not long after Erathosthenes and Posidonius, reported their results and noted:
"if of the more recent measurements of the Earth, the one which makes the Earth smallest in circumference be introduced--I mean that of Posidonius who estimates its circumference at about 180,000 stadia, then. . . "
and he continues:
"Posidonius suspects that the length of the inhabited world, about 70,000 stadia, is half the entire circle on which it had been taken, so that if you sail from the west in a straight course, you will reach India within 70,000 stadia. "
Notice that Strabo--for unclear reasons--reduced the 250,000 Stadia of Eratosthenes to 180,000, and then stated that half of that distance came to just 70,000 stadia. Handling his numbers in that loose fashion, he could argue that India was not far to the west.
Columbus Again
All these results were known to the panel of experts which King Ferdinand appointed to examine the proposal made by Columbus. They turned Columbus down, because using the original value by Eratosthenes, they calculated how far India was to the west of Spain, and concluded that the distance was far too great.
[IMAGE: Columbus]
Christopher Columbus
Columbus had an estimate of his own. Some historians have proposed that he used an argument like Strabo's, but Dr. Fischer found his claim to be based on incorrect units of distance. Columbus used an erroneous estimate by Ptolemy (whom we meet again), who based it on a later definition of the stadium, and in estimating the size of the settled world he confused the Arab mile, used by El Ma'mun, with the Roman mile on which our own mile is based. All the same, his final estimate of the distance to India was close to Strabo's.
In the end Queen Isabella overruled the experts, and the rest is history. We may never know whether Columbus knowingly fudged his values to justify an expedition to explore the unknown, or actually believed India was not too far to the west of Spain. He certainly did call the inhabitants of the lands he discovered "Indians," a mislabeling which still persists.
But we do know that if the American continent had not existed, the experts would have been vindicated: Coumbus with his tiny ships could never have crossed an ocean as wide as the Atlantic and Pacific combined. In hindsight the exploration of the unknown may be justification enough!
As for the size of the Earth, it was accurately measured many times since (see item "geodesy" in an encyclopaedia), one notable effort being that of the French Academy of Sciences in the late 1700s. Their aim was to devise a new unit of distance, equal to one part in 10,000,000 of the distance from the pole to the equator (as Eratosthenes showed, it is enough to measure part of that distance). Nowadays that distance is known even more accurately, but the unit introduced by the French academy is still used as the standard of all distance measurements. It is called the meter.