A sidereal day is the time it takes for the Earth to complete one full rotation on its axis relative to the distant stars. This period is approximately 23 hours, 56 minutes, and 4 seconds. Unlike a solar day, which is based on the position of the Sun, a sidereal day measures the Earth's rotation against the backdrop of the cosmos. The concept of a sidereal day is important in astronomy and navigation, as it helps astronomers track celestial objects. By understanding sidereal time, scientists can accurately predict the positions of stars and planets in the night sky, aiding in various astronomical observations and calculations.