Independence and self-links. Sky Atlas is independently published and edited by Zhou Zhe. It operates the portrait tool and the Sky Atlas guides linked in this article, so those are self-links rather than independent endorsements. This guide has no sponsorship, paid placement, or affiliate relationship with IANA, IETF, the Hong Kong Observatory, NOAA, or any other cited source. Sky Atlas has no affiliation with any government body, astronomical organization, calendar authority, certification organization, or regulator. It does not provide personalized readings or guarantee an astrological outcome.
Answer first
The Gregorian date, Chinese lunar calendar, twenty-four solar terms, IANA time zones, daylight saving time, and true solar time answer different questions. The portrait resolves them in sequence before calculating the Four Pillars.
A solar term is an astronomical instant, while a lunar date is a calendar position. A time zone is a set of historical civil rules, not a fixed offset from UTC. True solar time adds longitude and the equation of time to the civil clock.
The conversion order used by this site
The user states a local civil moment.
The historical offset and daylight-saving rule are resolved.
The astronomical calendar can be compared to one instant.
Calendar position and surrounding solar-term instants are identified.
The selected boundary conventions then produce the pillars.
The optional true-solar-time branch occurs before the pillar structure is calculated: the clock time is corrected with longitude and the equation of time. It is a separate convention, not a correction hidden inside “local time.”
Gregorian, lunar, and solar-term calendars are not the same
节气 Solar termsjié qì
The term often translated as “joints and breaths.” Lichun, the Beginning of Spring, is one of the twenty-four and is used here as the year-pillar boundary.
农历 Chinese lunar calendarnóng lì
A lunisolar calendar with lunar months adjusted to the solar year. The popular name includes agricultural associations; the technical rules still require a specific convention.
Time zones are historical rules, not fixed numbers
A city’s UTC offset can change across a year because of daylight saving time and can change across decades because historical rules differ. This site resolves the city through the IANA time-zone database before performing further calendar work.
The civil clock is used directly. The sample hour pillar is 壬午.
The corrected clock is about 60 minutes earlier in this sample because daylight-saving time and longitude shift the clock relative to local solar time.
The two columns are not two claims about which person is “real.” They show how a stated convention changes the hour pillar. A site that silently changes this input cannot claim to be reproducible.
Solar-term boundaries can change more than one pillar
On 4 February 2024 in Shanghai, the Lichun instant falls between 15:00 and 17:00. A chart shortly before and shortly after that instant can change the year pillar and the month pillar because both use solar-term boundaries in this implementation.
Year pillar 癸卯.
Year pillar 甲辰.
The change is not a contradiction inside one convention. It is a boundary crossing. Near the boundary, the tool should expose the alternative rather than silently choosing a side.
Unknown time is not the same as noon
No hour pillar is invented when the birth time is unknown. The tool omits the hour column and does not assume that every unknown time is noon, midnight, or the middle of a Zi hour.
A time range can reduce uncertainty, but it still does not justify pretending that every clock minute inside the range is identical. The portrait lists distinct pillar positions found at the endpoints and 30-minute samples. A manual IANA zone can establish civil time, but it has no coordinates for longitude-corrected true solar time.
What this does not mean
- A daylight-saving shift is not a mystical event; it is a civil-clock rule.
- True solar time is not a universal rule silently shared by every school.
- A solar-term date is not precise enough when a birth sits at the boundary moment.
- A known date without a time does not determine an hour pillar.
- A more precise clock does not turn a symbolic structure into a scientific prediction.
Precision at the input layer improves reproducibility. It does not resolve every interpretive question downstream.
Sources
- IANA, Time Zone Database, accessed 2026-10-21, for IANA identifiers and historical offsets.
- IETF, RFC 9557: Date and Time on the Internet, accessed 2026-10-21, for time-zone-aware timestamp representation.
- Hong Kong Observatory, Gregorian-Lunar Calendar Conversion Table and The 24 Solar Terms, accessed 2026-10-21.
- Sample values and true solar correction are generated by the project engine; the choice to display both clock and solar variants is an editorial convention.
Next step
Compare two conventions on purpose.
The disagreement guide shows how boundary choices, true solar time, and local time-zone mistakes can produce different charts.
Why calculators disagree