Over the past several years, we've been hearing more about various people believing that the earth is flat instead of spherical. Sometimes I am amused at people for taking this notion with even a modicum of seriousness, and I am also amazed that Americans in the year 2018 can actually give it any consideration.
Aside from being somewhat funny --quite frankly, if someone is at all serious in believing in a flat-earth, I can't take the intellectual, logical, scientific or theological considerations seriously from such a person. Maybe they would be good for "comic relief" in a discussion, but I put a fairly low value on their ability to analyze or understand reality or most serious topics.
One slam-dunk proof of a spherical earth is: Video. The fact that we can see that there are only spherical planets in the solar system, and we see them rotating. Everyone with a computer and the internet may (for example) get onto YouTube and look up "video of the rotation of Mars" which was recorded by cameras in space. --Mars is clearly spherical ...and rotating. Some videos even show a geographical pole on Mars rotating! And maybe you could even get some time on a fairly powerful telescope and watch the rotation happen for yourself! (If you can trust your own eyes.) --Then ask yourself: "Why isn't there a 'flat-Mars' society?" --Here is why: It would be silly, because everyone can see that it is spherical.
And then there's Jupiter. You can watch video of it rotating ...with the big orange spot, and the smaller orange spot going around. --And there is Saturn. Dial up the video and watch it rotate as well. They --along with all the planets and the sun-- are spherical and you can watch them rotate. It's so obvious. --Pictures (and telescope observation) of all the other planets show them to be spherical as well.
And finally, you can go back onto YouTube and watch space-borne camera video of the earth itself rotating the very same way! It is spherical and you can see the continents going around --with a rotating pole visible on the bottom (or top). -- Why would the earth's spherical form be any different from all the other planets and the sun, which are spherical?
In addition, you can get on the internet and watch video taken of the earth from weatherballoon flights bearing cameras at about 70,000 feet. You can see the curvature of the earth directly.
There is a reason every planet is spherical: Because any body the size of the dwarf-planet Pluto (with a 1500 mile diameter) --or larger-- is round because the large amount of gravity in bigger bodies makes even "solid" elements behave basically like an extremely thick, viscous liquid, which very slowly "flows" as close as it can toward the center, which forces the body to be spherical. Mars' diameter is 4200 miles. Earth has an 8000 mile diameter. Many elements deeper than 50 miles beneath the surface have this sort of thick, oozing, "plastic-like" consistency. Thus, Earth's massive gravity forces it to be quite spherical. (There is, therefore, an approximate limit to how tall mountains can be on earth). ...Only relatively "small" things like smaller asteroids can be quite "flat" or elongated, because their gravity is relatively weak. --Even the large asteroid Ceres (600 mi diameter) is fairly spherical.
For another personal experiment and "proof" that earth is spherical: Some day, at 12 noon where you are (e.g. in the middle of the mainland USA), you can make a conference-call with one person in California, and others in N.Carolina, Hawaii, and another in Australia (or New Zealand) and include somebody else in Europe into the conference call. When you've got them all on the line, ask all of these people where they observe the sun to be in the sky, and also what time of day it is in each place. Write down the data from all these people. (It won't even be day time for one of your people.) --You might also ask these people (the ones where it is day-time) to take meter-long measuring sticks out in the sun and stand them vertically to the ground, and ask each person whether the shadows of the sticks are pointing in a mostly easterly or a westerly direction, and how long the shadows are, and whether they are lengthening (in the afternoon) or shortening (in the morning). At 12 noon your time, the shadow for your stick will be very short. --Then think about it: The only conditions that will make sense of all these sun-positions and times and shadow-lengths and movements (all happening concurrently), is a spherical earth that is rotating. --If the earth were flat, the shadows on all the sticks would be the same length and be pointing in the same direction. But this is not the case, because the earth is spherical.
...To illustrate the above situation for yourself: In a dark room, shine a big flashlight across the room toward the equator and the longitude where you are on a globe, and stick several little 2cm length pieces of toothpicks vertically relative to your location and vertically relative to each of your people's locations across the face of the earth, and think about all the times and shadows reported to you. --Confirm that the earth is spherical.
And then also consider this: During any lunar eclipse, every time one sees the earth's shadow partially covering the moon, the shadow from the earth is round --not flat. --And very importantly: When a lunar eclipse is happening right at dusk (where observers are) here on earth, if the earth were flat to any significant degree, the earth's shadow on the moon would be quite flat at such a point in time, because the sun's rays would be passing straight past the surface of a flat earth and then hitting the moon. --But the earth's shadow is never flat at all --at any time. Earth's shadow on the moon is always round ...because earth is spherical. --The flat earth idea fails.
It's odd in 2018 --in a modern country-- for a person to believe in a flat earth. And yet it occasionally happens, so, I think it's a demonstration of the poor education a lot of people have. It also shows the irrational/illogical cynicism in many people that makes them see too many things as "conspiracies." They've seen too many computer-generated scenes in movies, and believe too many half-baked folktales. They don't trust significant institutions of learning or experts. They almost can't even trust video photography! They can't seriously consider the observations of serious and intelligent observers and scientists who are trying to understand things and to help all of us to understand.
-- With that kind of illogic applied, they wouldn't be able to believe records of history either, such as concerning Abraham Lincoln, George Washington, the Kings of England, the Roman Empire, nor Jesus Christ.
However, it is important to realize that various important Science Facts Confirm the Bible... including the fact that the Bible affirms the earth to be spherical --appearing "round" no matter at which angle one observes it.
And besides all this... you, dear reader, are loved and valued by God, who sent Jesus Christ to pay the death-penalty for the sins of anyone who will surrender and entrust their life to him. (see John 3:16 and Rom. 10:9).
Blessings to you!