Apparent solar time [1]: The time interval when the center of the sun's apparent circle goes up to the sky twice in succession is called true solar day. 1 The true solar day is divided into 24 apparent solar hours ... See (Birth Time and Destiny) for details. This time system is called apparent solar time. Apparent solar time is measured by the hour angle of the center of the true sun's apparent circle, and its starting point is noon in apparent solar time. In our daily life, the customary starting point is midnight (noon), just 12 hour apart. Therefore, in order to be consistent with people's daily habits, the apparent solar time is defined as: the hour angle of the center of the true sun's apparent circle plus 12 hour. Because the apparent solar time is obtained by observing the center of the sun's apparent circle, it is also called apparent solar time, or simply apparent solar time. Namely: apparent solar time = average solar time+true average solar time difference.
Apparent solar time must be used to calculate constellations. In ancient times, when using the apparent sun. The ancients decided: sunrise and sunset, noon on Sunday. The ancients set the time by erecting a pole to measure the shadow of the sun. There are still many ancient sun shadow stations in Xi, Xianyang and Henan. You are right. When looking at old photos locally is looking at the sun, the modern saying is "time difference".