What are some reasons to believe the earth is round?

Answer 1

Answer 1:

It's actually an oblate spheroid. We can know a few ways.

1. Pictures from space show that it is.

2. The shadow Earth casts on the Moon at times show that it is.

3. If you board a plane, and fly east, and keep doing so, eventually you'll return to where you started.

4. If Earth were flat, those on the edges would be gravitationally attracted to the center, not straight down as they are.

Answer 2:

Look how big it is. Everything that big is a sphere. Even the moon is a sphere.

Answer 2

Any sufficiently large mass (enough to counteract strength of materials composing it) will "collapse" to a spherical shape because that is the greatest volume for a given radius.

In simple terms, all the mass tries to squeeze as tightly together as possible. For smaller objects (people, ships, aircraft, asteroids), the compressive and shear strength of the materials making them up are greater than the gravity - and thus can retain essentially any shape.

So, rocky bodies can be aspherical (elongated, etc.) at a greater mass than icy bodies (which is less dense but holds far less strength).

Beyond this size (which is from 200 to 1,000 km in size), gravity becomes so strong that no natural material can resist it. If Earth were given enough time (many trillions of years), with no infusion of outside energy, all buildings would collapse, the continents would sink, and the oceans would cover all, until the entire planet was neatly divided into layers of increasing density, perfectly spherical and as smooth as a pane of glass.

The evidence for Earth's spherical shape is just about everywhere. Contrary to popular modern belief, humans have known the Earth was round since well before the Birth of Christ. The Early Greeks and Romans attempted to measure Earth's diameter, with varying degrees of success, but the orientation of the pyramids in Egypt suggests they may have known it to a high degree of precision.

It was quickly evident, for example, for Astronomers, that stars rose at different times in different places, and rose to different heights above the horizon depending on how far North or South they ventured - only possible if Earth were spherical.

As for Christopher Columbus, he didn't set out to prove the Earth was round - it was assumed that it was by his sponsors. However, he lied about the size, assuming the Earth was smaller to "prove" that he could find an easier passage to India by traveling Westward rather than down around the Southern tip of Africa and all the way back up the other side. Unfortunately (for him, Fortunately for us), he bumped into the West Indies (the Caribbean islands) which stood in the way.

For sailors, the oceans proved to be a good place to see the effect first hand, because water has no compressive strength unless confined (which it isn't), and thus attains as level a surface as possible given all the forces acting upon it (wind creates waves, The Sun and Moon's gravity raises tides, etc.). When the ocean is calm, it is easy to watch a ship disappearing below the horizon - or, if one were in a ship themselves, the receding land mass would disappear likewise. This is only possible on a curved surface. If the Earth were perfectly flat, the land would simply rise up directly to "eye level" no matter how high off the surface one was.

In a ship, it is easy to assume that it does, as it comes very close, but the higher one goes in an aircraft, the more the horizon appears to drop. Even so, this effect would be difficult to see without measuring it directly. However, in orbiting spacecraft, the effect is very noticeable. From above the atmosphere, the Earth is quite obviously a gigantic ball.

This brings to mind the most obvious proof. Spacecraft like the Shuttle travel in a straight line, curved only by the continuous freefall in gravity. And yet, these vehicles circle back to a point 15 degrees West of their starting point (as the Earth is continually spinning underneath at 1/16th the rate of low Earth orbit).

Were the surface flat, Spacecraft would simply disappear off to the East and crash land a few tens of thousands of kilometers to the East. Changing orbits significantly takes extraordinary energy, and to simply "hover" over some spot above the surface would be outright impossible for more than a few minutes, much less turning around to return to the starting point.

Sorry about the long winded answer, but that pretty much covers all the angles.

Answer 3

The earth has been proved to be round like a sphere because there are cameras and satellites to prove that the earth is round, just because the earth is round doesn't mean that it is a perfect sphere. It has bumps and isn't all even.
Pictures from space

Answer 4

The horizon suggests that the surface curves away from our line of sight, and images from space pretty much prove that Earth is roughly spherical (momentum forces it to wider at the equator and flatter at the poles).

Answer 5

Obviously there is satellites that orbit the Earth and it is in a spherical shape..

Answer 6

we have proof that the earth is round because we have satellites and that take pictures.

And when they travel to space they can see it

Answer 7

It casts a round shadow during a lunar eclipse.

Answer 8

because of its atmosphere