Yes, the sun cannot illuminate the whole earth at once when the earth is lit on one side it is day and when it is on the other side it is night. The earth rotates on its own axis which causes change of day and night. Due to this rotation, those areas which are in front of sun experience day while on the other hand, the shade part of the earth causes night at that part so we can say that diurnal rotation is responsible for day and night.
B) wavelength Notice how Z goes from one wave's crest (top) to another's crest. Wavelength can also be measured from a wave's trough (bottom) to the next one's trough.
