All they have to do is step outside and observe the phases of the moon and they'd see that the earth is spherical
The ignorance of your comment is mind-numbing.
There's a book you should really consider reading: it's called the Bible.
If you read it, you will hear Our Lord explain to you the DIFFERENCE between the celestial bodies and the earth. Earth is NOT a celestial body. Therefore, your assumption that the earth should be the SAME as the MOON based on appearance of the moon is in direct CONTRADICTION to Our Lord's teaching:
"
All flesh is not the same flesh: but one is the flesh of men, another of beasts, another of birds, another of fishes. And there are bodies celestial, and bodies terrestrial: but, one is the glory of the celestial, and another of the terrestrial. One is the glory of the sun, another the glory of the moon, and another the glory of the stars. For star differeth from star in glory. " I Cor. 15:39-41