The Empire uses "standard time - the hours, days, and years of Earth - to maintain a constant measurement of time throughout its territory. While residents of other planets and space habitats often also have "local time" based on the length of the local day or year, they must remain aware of the current standard time. (Imperial worlds measure local time in standard increments; for example, the planet Sappho has a day "four standard days" long.) Starships maintain standard time exclusively.