FE cannot have a circle to separate day and night, but when a light shines on a globe the boundary between the illuminated side and the dark side becomes a circle.
Job 26:10 ESV - He has inscribed a circle on the face of the waters at the boundary between light and darkness. 
Isaiah 40:22 ESV - It is he who sits above the circle of the earth, and its inhabitants are like grasshoppers; who stretches out the heavens like a curtain, and spreads them like a tent to dwell in; 
Isaiah 40:22 APB - He is the one controlling the curve (G1135.1) of the earth (G1093), and the ones dwelling in it are as locusts; He is the one establishing [as a vault the heaven], and extending it out as a tent to dwell in;
(Debunks the FE "flat" claim - "curve" is derived from G1135 "a woman; wife" and H2328 "a circle"...the cross section of a flat surface is not a circle, nor does it resemble a woman)