Astronomical time refers to the measurement of time based on the positions and movements of celestial bodies, such as the Sun, Moon, and stars. It is often used in astronomy to track events like the rising and setting of these bodies, which helps in understanding the cycles of day and night, as well as the changing seasons. One common system of astronomical time is Universal Time (UT), which is based on the Earth's rotation. Another important concept is sidereal time, which measures the time it takes for the Earth to rotate relative to distant stars. These systems help astronomers coordinate observations and understand the universe's dynamics.