True Solar Time, The Equation of Time, Sundial Time
The theory of Chinese Five Element Horoscope is based on Chinese Yin and Yang. Yin is connected to dark, cold, night, and female. Yang is connected to bright, hot, daytime, and male. While observing the life cycle of plants, the Chinese applies those phenomena to the life cycle of a human. The cycles of the Sun change the weather, temperatures, four seasons, which impact people's life. Therefore, the Chinese Horoscope calendar is derived from the Sun. Many people thought the Chinese Horoscope calendar is a Chinese Lunar Calendar. In fact, Chinese Horoscope adopts the solar calendar.
Our clock tells us that we have 24 hours a day. But, Earth rotates once is not exact 24 hours every day. Most days are either longer or shorter. Also, the Earth's orbit around the Sun is not a perfect circle but is slightly oval. That means the Earth's orbital speed is changing throughout the year. The fastest speed is at the solstices, and the slowest speed is at the equinoxes. The time shown by clocks is called mean solar time or Greenwich mean time (GMT). The true solar time is observed by the position of the Sun in the sky. The moment of the midday should be the time when the Sun appears highest in the sky on the day. The Equation of Time is a measure of the variation in the length of each day through the year. Over the year, true solar time can deviate from mean solar time by more than 15 minutes.
The sundial is a tool to read time during daylight hours from the position of the Sun. Therefore, sundial time is also called apparent solar time. The formula of the Equation of Time is below.
Equation of Time = Sundial Time minus Local Mean Solar Time
The Mean Time is the clock time, the standard time of the time zone. The Local Mean Time is the longitude time. The true solar time = Local Mean Time + Equation of Time. For example, a person was born on October 10, 2019, at 11:00 a.m. The birthplace is the city of Los Angeles at the US Pacific Standard time zone. The longitude of Los Angeles is 118.2437 west. One degree is 4 minutes. Therefore, the Local Mean Time is 11:06 a.m. From the chart of the Equation of Time, October 10 is 12.5 minutes. The sundial time (true solar time) = 11:06 a.m. + 12.5 minutes = 11:19 a.m. The birth time becomes 11:19 a.m.
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By Master Allen Tsai on January 12, 2022