Diurnal motion is the apparent daily motion of stars around the two celestial poles due to Earth’s rotation. The stars move in a peculiar way that can only be explained in the spherical Earth model.
All the differences of diurnal motion that occur in the different latitudes on can never be explained in a flat Earth.
In the northern hemisphere, stars rotate counterclockwise around the north celestial pole. Stars above the north celestial pole move rightward, and stars below it move leftward. Facing south, stars move rightward, or westward.
In the southern hemisphere, the reverse happens. Stars rotate clockwise around the south celestial pole. Stars above the south celestial pole move leftward, and star below it move rightward. Facing north, stars appear to move leftward, or westward.
On the equator, the motion observed in the northern and southern hemisphere above can be seen simultaneously, with the difference that the circular motions are cut in half by the horizon. Facing east, stars appear to rise. And conversely, facing west, stars appear to set. Not unlike the Sun.
The north celestial pole appears higher in the sky as we travel more to the North. And the same thing happens in the south too: the south celestial pole appears higher in the sky as we travel more to the South.
All of these can never be explained in the flat-Earth model. Once our ancestors gained the ability to travel over a greater distance, the difference of diurnal motion was quickly noticed. And just as quickly, the flat-Earth model was abandoned, to be replaced by the much more plausible spherical Earth. We can say that the unfortunate prominence of flat-Earth today is a result of the severed relationship between us and the stars. Stars are no longer essential to our daily lives.