What Is the Earth's Motion That Causes Day and Night?

earth-s-motion-causes-day-night Credit: Gary Waters/Ikon Images/Getty Images

The spinning and rotating movement of the earth along its vertical axis causes the difference between day and night. The differences between light and darkness on the earth's surface are caused primarily by the earth’s rotation along a vertical axis. This constant spinning motion accounts for hourly changes in light and produces long-term changes in daylight hours through the seasons.

At any given time, half of the earth is cast in the shadow of darkness while the other half is bathed in light. The earth rotates vertically but shifts horizontally too: this tilt accounts for prolonged changes in light and darkness that coincide with changing seasons. The daily patterns of sunrise, noon and sunset at all points on earth are heavily influenced by the 24-hour rotation cycle, which causes different conditions simultaneously around the globe. Although some days have fewer hours of sunlight and others longer, the difference averages out so that all areas of earth have equal times of daylight and darkness. Each time the sun spins around its axis, a fixed point on the earth’s surface is cast into light and later into darkness. During the morning, the sun appears as a thin line above the horizon, gradually expanding over the sky into noon before setting again in a thin line, completing the cycle.