Why Time Zones Make or Break a Chart

An error of just 1 hour can shift the Ascendant by ~15 degrees, changing the entire chart. Here is how we handle the complexity of global time.

The Stakes are High

In Astrology, the Ascendant (Rising Sign) changes approximately every 4 minutes of time. A simple Daylight Savings Time (DST) error of 1 hour can result in:

• Wrong Ascendant Sign (~50% chance)
• Incorrect House Cusps (All houses shift)
• Wrong Moon Nakshatra (if borderline)
• Incorrect Dashas timelines (shifted by years)

Historical Context: LMT vs Standard Time

Before the late 19th century, most locations used Local Mean Time (LMT). Noon was determined by the sun's position at that specific longitude.

For example, "noon" in Mumbai was different from "noon" in Delhi.

The Standardization Shift

Countries adopted Standard Timezones at different dates:

• USA: Late 1883
• UK: 1880
• India: 1906 (Shifted from Madras Time to IST)

Calculating a chart for 1890 using modern "Asia/Kolkata" (+05:30) time would be incorrect. You must use LMT, which is calculated precisely from the longitude.

How We Handle It: "AUTO" Mode

Our API includes a sophisticated time-resolution engine. When you send tz_str="AUTO", we perform a multi-step verification:

1. Geographic Lookup: We determine the precise IANA timezone ID (e.g., "America/New_York") from the latitude and longitude.
2. Historical Validation: We check the birth year against our database of standardization dates for that region.
3. Algorithm Selection:
   • Modern Dates: We use the IANA database to handle DST offsets automatically.
   • Historical Dates: We switch to LMT calculation based on the precise longitude.

BaZi Time Standards (Chinese Astrology)

Chinese Astrology (BaZi) requires high precision for the Hour Pillar. Practitioners often disagree on whether to use "Clock Time" or "Solar Time." Our API supports all three major standards:

1. Civil Time (civil): The raw local clock time. Recommended for users who want to match apps like BaZi-Calculator.
2. Relative Solar Time (true_solar): Adjusts for your longitude relative to the timezone meridian. It preserves the "hour of the day" feel (noon is roughly 12:00) while accounting for being at the edge of a large timezone.
3. Absolute Solar Time (true_solar_absolute): Pure astronomical sundial time (UTC + Longitude Offset + Equation of Time). This is the most technically "accurate" solar time but may result in pillars that feel "shifted" from local expectations.

[!TIP] Use Relative Solar if you are calculating charts for large countries (China, USA) or frontier cities like Paris to ensure the most balanced astrological results.

Best Practices for Developers

1. Always use coordinates: City names are ambiguous. Lat/Lng is absolute. Our API prioritizes coordinates for timezone detection.
2. Trust "AUTO": Unless you are an expert astrologer with a verified source for a specific timezone offset, let our engine handle it.