The ==Key Stage 2=====Meaning===A [[day]] is the time it takes for the [[Earth]] to spin around once. ===About a Day===: A [[day]] lasts 24 [[hour]]s. ==Key Stage 3=====Meaning===A day is the time it takes for a [[planet]] to spin around once. ===About Days===: A [[day]] on [[Earth]] lasts 24 [[hour]]s.: A daytime and nighttime are caused by the [[Earth]] spinning around on its [[axis]].