Which solar time is based on the actual Sun’s apparent motion in the sky?

• A. Mean Solar Time
• B. Apparent Solar Time
• C. Sidereal Time
• D. Universal Time

Answer: (B)

Apparent Solar Time measures time by the Sun’s actual position in the sky as observed from your location. It shows solar noon when the Sun crosses the local meridian, and its value shifts through the year because the Sun’s apparent speed in the sky changes due to the ellipticity of Earth’s orbit and its axial tilt. This variation is described by the equation of time, so apparent solar time can differ from a clock by as much as about 16 minutes at different times of the year. Mean Solar Time, by contrast, uses a fictitious Sun moving at a constant rate to keep day length uniform. Sidereal Time is based on the reference frame of distant stars, not the Sun, and Universal Time is a standard linked to mean solar time at Greenwich (Earth’s rotation) rather than the Sun’s instantaneous position. So the time reading that follows the Sun’s actual apparent motion is Apparent Solar Time.