It is because the Earth is rotating on its axis that we see the sun and stars move across the arc of the sky. Motion – it’s everywhere in the universe. Nothing is really standing still. We humans ride on a sphere that spins on an axis as it revolves around a star, a rotating star in orbit with 100 billion other stars in a whirling galaxy that’s moving over 1 million kilometers an hour in an expanding universe. Some of this motion can be viewed over the course of a few minutes, and some requires centuries or millennia to be perceived. Over thousands of years, our ancestors have recorded the repeating events they saw in the sky.
They weren’t able to explain them and worshiped the sky bringing the power and the order of the sky down to Earth for part of their culture. Modern stargazers have the advantage of knowing what causes the motions of the Sun, Moon, planets, and stars. But that only increases their admiration for the ancients’ ability to track these celestial cycles. When studying the sky for any length of time, like ancient astronomers did, we find very obviously that there is a series of cycles, and these cycles all have different periods to them and Earth rotation on its axis is one of the many celestial cycles we see in the universe in constant motion.
It’s obvious to anybody, really is the daily cycle, what astronomers call the diurnal cycle. The daily motions, the diurnal cycle we see in the sky are caused by the rotation of the Earth on its axis. When viewed from above Earth, the North Pole, the Earth spins in a counterclockwise direction, eastward (from west to east),. It makes a complete rotation of 360 degrees in a little less than 24 hours (more precisely 23. 9 hours). For this reason, when viewed from the Earth’s surface, the Sun, Moon, and stars appear to rise in the east and set in the west, making a complete rotation of 360 degrees in a little less than 24 hours.
So here we are on the Earth, it’s a big, spinning ball. But to us, attached to this ball, we see the sky moving around us once a day. So you see the Sun rise and the Sun set, the stars rise and the stars set. And that takes, we know, roughly 24 hours. As we see, Earth rotates about its axis at approximately 15 angular degrees per hour. Rotation dictates the length of the diurnal cycle (i. e. , the day/night cycle), and creates “time zones” with differing local noons. Local noon occurs when the Sun is at the highest point during its daily skyward arch from east to west (i. e. , when the Sun is at its zenith on the celestial meridian).
