Apparent solar time is a term used in astronomy that refers to the time kept by the apparent motion of the sun across the sky. The spelling of the word "apparent" is [əˈpærənt], with the primary stress on the second syllable, and the vowel in the first syllable pronounced as schwa [ə]. The word "solar" is pronounced [ˈsoʊlər], with the primary stress on the first syllable and the second syllable pronounced as schwa [ə]. The word "time" is pronounced [taɪm], with the primary stress on the first syllable.
Apparent solar time refers to the time determined by the position of the Sun in the sky, taking into account the Earth’s rotation and the observer’s location on the Earth's surface. It is a measure of time based on the Sun's actual position and movement, which varies from day to day due to the Earth’s elliptical orbit and axial tilt.
Unlike standard solar time, which divides the day into equal intervals, apparent solar time reflects the true solar noon or midday when the Sun reaches its highest point in the sky. This means that apparent solar time can differ from the time displayed on traditional clocks or watches, which are based on mean solar time, a uniform timekeeping system that averages out the variation in the Sun's position.
To calculate apparent solar time, one must consider the longitude and latitude of the observer as well as the equation of time, which accounts for the discrepancy between mean and apparent solar time due to the Earth's orbital eccentricity and axial tilt. The equation of time allows for the conversion of mean solar time to apparent solar time.
Apparent solar time is used in various applications such as astronomy, celestial navigation, and sundials. It provides a more accurate representation of the Sun’s position and allows for the precise determination of sunrise, sunset, and other astronomical phenomena based on the observer's location.