Imagine standing beneath the night sky at the Xinglong Observatory in Hebei, with your camera focused on Polaris for a long exposure. You'll see countless star trails forming arcs. These aren't stars moving—they're actually our planetEarthslowly rotating beneath our feet.

1. Essence and Direction of Motion

The rotation of Earth around its own axis is called Earth's rotation. The direction of rotation iswest to east. When viewed from the poles, follow the rule 'counterclockwise in the north, clockwise in the south': counterclockwise when seen from above the North Pole, clockwise from above the South Pole.

2. Two Time Scales

• Sidereal Day: The true period of Earth's rotation (360°), lasting 23 hours 56 minutes 4 seconds.
• Solar Day: The reference for our daily routines, lasting 24 hours.

3. Spatial Patterns of Speed

Earth's surface points do not move uniformly:

• Angular velocity: Except at the North and South Poles, angular velocity is equal everywhere—approximately 15° per hour.
• Linear velocity: Significantly influenced by latitude, decreasing from the equator (~1670 km/h) toward the poles, reaching zero at the poles.