all you need to do is stand at the pole during polar night to prove Earth's curveture, the Sun does not make it above the horizon.
As far as crescent photos of the planets proving their spherical shape browse for Venus or Mars.
Yes they tend to get cooler the further you progress away from the REAL Sun, not the flat earth christmas tree bulb Sun.
the graphic provided does not prove a flat earth sun, it (the sun) would still be visible in the polar night above the horizon in regards to that graphic, it could not would not go below the horizon at the poles.
Or anywhere for that matter in a flat earth.
The graphic is a prelude to constant daylight w/o sunset or rise It simply is Not a viable theory to flat earth.
Mamboni is proving a pyramid or christmas tree earth if anything