Final answer:
The day/night cycle of Earth is caused by the planet's rotation on its axis every 24 hours, not the sun revolving around Earth or the orbit of the moon. This rotation causes different parts of the planet to face towards or away from the sun, resulting in day and night.
Step-by-step explanation:
The cause of the day/night cycle on Earth is the rotation of Earth on its axis every 24 hours, which alternately exposes one side to the sun and then the other, creating day and night, respectively. It is not caused by the sun revolving around Earth, the moon's rotation around Earth, nor Earth's orbit around the sun. However, Earth's orbit and the 23.5° tilt of its axis are responsible for the changing seasons, but not the day/night cycle.
It is a common misconception that the sun revolves around Earth in a 24-hour period or that the changing distance between Earth and the Sun throughout the year causes the seasons. In reality, the distance variation due to Earth's elliptical orbit is only about 3%, which is not enough to cause significant variations in temperature. Instead, the tilt of Earth's axis means that when the Northern Hemisphere is tilted towards the Sun, it experiences summer, and when it is tilted away, it experiences winter, with the opposite occurring in the Southern Hemisphere.