The apparent motion of stars across the sky is primarily caused by the rotation of the Earth on its axis. The exact speed at which stars appear to move across the sky depends on several factors, including the observer's location on Earth and the specific star being observed.
At the Earth's equator, the maximum speed at which stars can appear to move across the sky is approximately 15 degrees per hour, which is equivalent to one degree every four minutes. This speed decreases as you move closer to the Earth's poles.
To put this into perspective, the apparent motion of stars is relatively slow and often difficult to notice without a reference point. It is more common to perceive stars as stationary due to their immense distances from Earth. Other celestial objects, such as the Moon and planets, may appear to move noticeably faster across the sky due to their proximity to our planet.