- Astronomy. local time measured by the hour angle of the sun.
- Solar time as measured by the Sun’s actual position with respect to an observer’s local meridian and equal for any observer to the hour angle of the Sun at that location. Sundials register apparent time, which differs continuously with the observer’s longitude and is not standardized across a time zone. Each degree of longitude represents a difference of four minutes in apparent time. Because of irregularities in Earth’s orbit and the tilt of its axis, a day as measured by apparent time varies somewhat in length throughout the year. Also called apparent solar time♦ The moment when the Sun crosses an observer’s local meridian is called the apparent noon. Compare local mean time. See more at mean time solar time.