UT1, or Universal Time 1, is a time standard that reflects the mean solar time at the Prime Meridian, located in Greenwich, England. It is based on the rotation of the Earth and is used as a reference for civil timekeeping. UT1 is one of several time standards, including UTC (Coordinated Universal Time), which is adjusted for leap seconds to account for variations in Earth's rotation. UT1 is measured in seconds from the midnight of January 1, 1970, and is expressed in terms of hours, minutes, and seconds. It is essential for applications in astronomy, navigation, and satellite operations, where precise timekeeping is crucial.