Why We Know..

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There are a myriad of reasons we can know the earth is round. All of these can be easily explained on a globe, not so much on a "flat earth."

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Sunrise and sunset.
Sun never changes size.
The sun sets bottom to top.(-- When driving towards a mountain you see the top first)
Shadows going under clouds at sunset.
Twilight (Its mere existence isn’t possible on flat earth)
The first attempt at measuring the speed of light.(The difference in IO obscuring
Can read a book 10 minutes before senset then cant see book.  Sun doesn't just go far away in 10 minutes.  It sets behind the curve. *
 
Moon never changes size.
Eclipses.
Same face of moon for everyone on earth on any particular day/night.
Same phase of the moon for everyone no matter where you are on the planet.
Tides on oceans and the great lakes.
 
Stars
Reciprocal Zenith Angles.
Northern star rotation is opposite to southern star rotation.
Retrograde planet movements.
Cant see Polaris from south pole, cant see Sigma Octantis from north pole.
Tall structures further apart at top than bottom, yet both are perpendicular to ground.
3 (or more) pointed Eratosthenes experiments (done by Riz and confirmed a globe.)
Southern hemisphere sun arc.
Gyroscopes experience a 15 degree per hour procession
 
 Other
Pressure gradient in the atmosphere.
Ships disappear from the bottom to top when they go over the horizon. (Same as the way a sunsets)
Seasons.
The prediction of Neptune, which is a result of our understanding of gravity.
Flight times and plane routes (ie – New Zealand to Johannesburg. Are trackable in real time on the web.)
Compasses don't work on a flat model. If you traverse the equator in a straight line, your compass needle will change)
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​This list was compiled by a trusted Globe Debate Proponent @round.hound.  I have validated each claim.

If you would like to propose an article please email mike@mikesplained.com