AstroLogics team ·
Historical timezones in birth charts
A birth time is what a clock showed. To place the planets, the engine needs the instant in universal time, so it needs the offset that clock was keeping on that day. "India is +05:30" is true today, and wrong for several stretches of the last century.
What India's clocks did
With "timezone": "auto", the API takes the offset from the timezone database for the place and date:
| Period | Offset |
|---|---|
| From 1906 | +05:30 |
| October 1941 to May 1942 | +06:30 |
| May 1942 to September 1942 | +05:30 |
| September 1942 to October 1945 | +06:30 |
| Before 1906 | +05:21 in the database, for all of India |
The two +06:30 stretches were wartime clocks, an hour ahead. Before 1906 the database has a single zone for all of India, but cities kept their own local time, so a birth before then needs an offset you know. See the birth object.
Other countries are the same story with different dates: daylight saving in the United States and Europe moves the offset by an hour twice a year, and its rules have changed over time.
How much one hour moves
Take a made-up birth on 15 June 1943 at 06:30 in New Delhi. The clock was on +06:30. Here is the same birth computed both ways:
"auto" (+06:30) |
Assumed +05:30 | |
|---|---|---|
| Lagna | Gemini 0.69°, Mrigashira | Gemini 14.46°, Ardra |
| Moon | Libra 16.60°, Swati pada 3 | Libra 17.17°, Swati pada 4 |
| First mahadasha (Rahu) ends | 18 January 1948 | 9 April 1947 |
An hour moves the lagna by about 14° and into another nakshatra, which changes every house-based reading. The Moon moves about half a degree, and because the dasha balance comes from the Moon, the first mahadasha ends nine months earlier.
What to send
- A place and
"auto", the default: the API looks up the offset for that place on that date, and says which it used inmeta.timezone_used. - A fixed offset, such as
"+06:30", when you know what the clock showed, for example from a birth certificate that names the time standard. - An IANA name, such as
"Asia/Kolkata", when the place is uncertain but the zone is not.
curl -X POST 'https://api.astrologics.in/v1/kundli' \
-H 'Authorization: Bearer al_test_YOUR_KEY' \
-H 'Content-Type: application/json' \
-d '{"birth":{"date":"1990-08-13","time":"06:30","place":{"latitude":28.6139,"longitude":77.209}}}'Check meta.timezone_used in the answer: "source": "auto" with "utc_offset": "+06:30" for this birth. If a client's chart differs from another calculator's by about an hour of lagna, the offset is the first thing to compare.