Yes, it is. The flat Earth is nonsense and it can easily be proven to be so by the fact that by the time it is getting dark in Japan and it is getting light in Europe which suggest that the Earth is at best cylindrical. No, if you take into account that during the winter it gets darker quicker the further you move to the North that implies a curvature along the vertical axis and therefore it has to be a sphere. If you want more sophisticated arguments I can tell you more.