While it might have been somewhat common knowledge 500+ years ago that the Earth was a flat circle (or more accurately a dome-like shape counting the arching atmosphere above it). Today it's pretty much common knowledge that the Earth is a 3-D sphere (also known as a planet): this is accepted as a scientific fact: that means it's absolutely true; Earth is a globe shape.

Except, if Earth being a sphere is actually not really a proven fact and is actually all the so-called 'facts/observations' that prove Earth is a sphere, are actually unproven lies that are presented as proven observations/facts by scientists/the scientific community that are purposefully hiding true facts that really show the Earth is a flat circle covered in a dome-like atmosphere. 

This is called the flat-Earth theory, it's what some people believe today is what has been going on with the shape of the Earth for about 500 years now: 

while different groups/beliefs in this theory conclude slightly different things this is the main belief that this theory is all about: 

It states most of the world has been told the lie that the Earth is a sphere when really it's a scientific (possibly political) conspiracy that purposefully hides the real scientific evidence showing Earth is a flat circle (with a dome shaped atmosphere). 

While to many people (especially educated ones) this theory (and especially the people that believe in it) is ridiculous and would be (and is) considered a joke to many and made fun of, as a Christian, I took this theory very seriously: I absolutely considered every theory I hear as possible truth: 

why? 

Well ,first off. this is how science (should) properly work: (As covered in the series "finding the truth") Science is just the way to most accurately find out what is a fact of reality and there's nothing wrong with new theories being presented to challenge old ones (even if they are well proven like the cell theory which are pretty much soo proven there treated like a fact: even though the Earth being a sphere is not a theory, it's a fact). 

And this theory especially should be considered in what it's saying is true: That there is a deliberate attempt to hide scientific observation/facts that would prove Earth is not a sphere: this statement alone should be very seriously considered not laughed off: because if it's true then not only is this very unscientific but it's a crime against science and is worthy to be investigated just for this reason. 

The other reason is, The Bible (the final authority for Christians) says to examine all things to see if their true:

1 Thessalonians 5:21

"Test [prove] all things; hold fast what is good"

So, as a Christian, it's my job to test this theory and see if it really is true and not just to accept it's false just because it sounds crazy or insane: so now that we've seen the theory the real question is it true or false?

Closely looking at the scientific observations/facts 

So lets look at the observations on what shape Earth is; by observing what we can and using logic and seeing which model/theory is the most accurate: 

The Best part about these observations is they can't be hidden; you can litterally go to these places and observe many of these things yourself: So we know for sure we are getting only accurate observations and facts to come to an accurate conclusion.

 Big differences in the Northern and Southern Hemispheres 

Because Planet Earth is supposed to be a sphere it is also can be (and often is) divided like a sphere: 

It's divided into two semi-circle halves called 'hemispheres' (with the upper half being the Northern Hemisphere and the lower half being the Southern Hemiphere) cut in equal halves at an imaginary line called 'the equator' where the sphere is bulged out from the rest of the curve.

Well, if the Earth is really a circle (or anyother shape for that matter) these lines mean nothing any more: There is no equal hemispheres since it's not a sphere, Therefore no equator to equally divided them. If Earth really is a circle then these lines should be imaginary.

Yet there are some very really observable diffrence happening in these hemispheres and even at the equator line.

Changes in celestial objects in sky at different locations on Earth 

One of the observations that strongly points to the shape of the Earth is how different celestial objects (that's objects that are seen in Earth's sky: mainly glowing objects like the moon, sun, and stars) are viewed in Earth's sky from the surface. Subtle changes in how their viewed to someone on different parts of Earth's surface, by logic, Determines how the Earth is ultimately shaped.

So how do these objects in the sky change as someone moves from different locations on Earth? 

Changes in stars and constellations traveling North and South

Most likely (especially if you can read this) you have seen stars up in Earth's clear night sky at some point and constellations they form too: 

However, the view of the constellations/stars changes drastically moving North and South on Earth's surface:

In fact, an entirely new set of constellations can be seen in the areas in one hemisphere that cannot be seen in the areas of the other hemispheres: 

For example, if you were viewing the constellations in the areas in the Northern Hemisphere you would see the constellations Ursa major (The big dipper), Ursa minor (little dipper),Orion, and even the famous northern star in the little dipper, Polaris, pointing north (towards the north pole).

However, if you traveled South to the area in the Equator line you would begin to see some of the constellations you saw North of the line slowly begin to set below the horizon and become harder to see (this is especially true of Polaris which is so close to the horizon in the equator it's practically invisible). but you would also begin to see new ones come up on the other horizon. 

If you continue traveling south past the equatorial line some of the constellations you saw north of the equator will dissapear entirely (especially the northern star, Polaris) and soon you would see an entirely different set of constellations in the night sky: instead you'll see The Southern Cross (Crux), Centarurus, and even the southern star ,Sigma Octantis, in the constelation Octans, pointing south (towards the south pole) however you can still see Orion but it looks upside down compared to how it looks in The Northern Hemisphere.

The fact that moving North and South to different Hemispheres (and over the Equator line) causes some constelations to disappear over the horizon and new ones to appear over another horizon, logically means something must be blocking the view of those constelations at those points to a viewer on Earth's surface. Since the constellations are blocked by the horizon at these diffrent locations means the Earth itself is blocking them. 

This logically only would happen if Earth were shaped like a sphere; this would explain why only certain constellations could be seen in only one hemisphere while others could not: 

Because those other constellations would be under the horizon or better put being blocked by the curve of the sphere.This also explains why on the equator some constellations are visible from both sides of the hemisphere are seen: because the equator is the where a sphere is equally split in half: in other words its' greatest 'bulge' is in the middle so this area  'sticks out' more than the other curves so constellations from both sides are visible.

If Earth was truly a flat circle with the stars being seen in the dome-like atmosphere above, then all of these constellations/stars (by logic) should all  be visible eveywhere on Earth no matter where your view them from (even though their location might change in the sky depending on where you are).

And if there's any major change to the constellations'/stars viewed it should be when traveling East to West definitely not North to South. But this is the completle opposite to what is actually observed: the major changes in constellations/stars is north to south not east to west. 

Also, some constellations disappear over a certain point over the equator (or on the equator itself) this should not happen on a flat Earth no matter how far North or South you move; because there should be nothing to block the completle view of a clear sky. 

Therefore, these observations strongly show Earth is not a flat circle but a 3-D sphere.