1) The Earth rotates on its axis once every 24 hours, causing day and night. It revolves around the Sun once every year in its orbit. 2) The tilt of the Earth's axis relative to its orbit around the Sun causes the seasons. Summer occurs when the northern hemisphere is tilted toward the Sun. 3) The phases of the Moon are caused by the changing angle of illumination by the Sun as the Moon orbits the Earth monthly. A lunar eclipse occurs when the Moon passes through the Earth's shadow.