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Apparent solar time

真太阳时

True solar time usually means local apparent solar time, defined astronomically. Whether a natal method should use it is a separate convention, not an astronomical conclusion.

Introductory article2 min readUpdated 2026-09-30AI-assisted · Editorially checked

At a glance

Astronomical definition
Local apparent solar time
Corrections
Longitude difference and equation of time
One instant, different time labels08:00 UTC and 16:00 UTC+8 identify the same instant. Apparent solar time also depends on longitude and the equation of time; historical daylight-saving rules require checking.08:00 UTC16:00 UTC+08:00+ 8 hCivil zone time ≠ local apparent solar time
One instant, different time labels08:00 UTC and 16:00 UTC+8 identify the same instant. Apparent solar time also depends on longitude and the equation of time; historical daylight-saving rules require checking.

Definition and terminology

Apparent solar time follows the Sun’s apparent position; a sundial displays it. Mean solar time averages that motion, while civil clocks follow time zones and sometimes daylight saving. These are different scales. Astronomy explains their relationship but does not decide which scale a particular divinatory tradition ought to adopt.

[1][2]

Structure and rules

After handling the civil offset and daylight saving, longitude correction relates local mean time to the zone meridian, at about four minutes per degree. The equation of time then relates apparent and mean time. If defined as apparent minus mean, add it; opposite sign conventions require the opposite operation, so document the definition.

[1][2]

Worked reading

For a teaching example, take a 120°E zone meridian and 115°E location with no daylight saving: the longitude correction is minus twenty minutes. Civil noon becomes local mean 11:40. With an explicitly hypothetical plus-five-minute equation of time, apparent time is 11:45. A real date requires astronomical data, not this assumed value.

[1][2]

Context and limits

Longitude correction alone produces mean solar time, not a complete apparent-time conversion. Records may be rounded or near midnight and double-hour boundaries, so preserve the civil time and algorithm. An astronomically correct conversion does not demonstrate superior natal prediction. Verifiable time calculation and divinatory effectiveness remain separate questions.

[1][2]

References & further reading

Historical sources document ideas and rules of their time, not empirical proof of predictive accuracy. Source notes identify the nature and scope of each reference.

  1. Hong Kong Observatory: Apparent Solar TimeInstitutional / reference source

    Official astronomical definition of apparent solar time.

  2. US Naval Observatory: The Equation of TimeInstitutional / reference source

    Official astronomical reference; explains apparent minus mean solar time.

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