Daily Lagna transitions

personal.lagna-transitions

Swiss Ephemeris houses and bisection locate ascendant sign changes through the day.

Assurance

Level	Current statement
Documented and traceable	Yes — the canonical record includes the process and a worked example.
Regression or reproduction checked	Linked to 2 repository test file(s).
Independently source-supported	Not independently verified at this level; current behavior is regression-pinned.

Computation method

Method type: algorithm

Compute the tropical Ascendant from Swiss houses, subtract Lahiri ayanamsa, scan sunrise to next sunrise at five-minute steps, and bisect every Rashi change to half-minute precision.

Process

1. Compute next sunrise and set Lahiri sidereal mode.
2. At an instant, obtain the Placidus Ascendant, subtract ayanamsa, normalize, and divide by 30 degrees.
3. Scan in five-minute Julian-day increments.
4. When the sign changes, bisect until the bracket is at most 0.5 minute and close the current Lagna window.
5. Append the final window through next sunrise.

Formulae

Sidereal Lagna index

r = floor(((asc_tropical - ayanamsa) mod 360)/30)

• r: zero-based rising Rashi index

Worked example

Hyderabad, 2024-01-01

Inputs

• Location: 17.385 N, 78.4867 E
• Day start: local sunrise 06:45:59 IST

Calculation

1. The sunrise Ascendant maps to Dhanu.
2. A five-minute scan brackets the next sign change and bisection refines it.

Result

• Dhanu Lagna: 06:45:59-07:47:23 IST
• Makara Lagna begins: 07:47:23 IST

Method notes

• The Python owner computes the transitions; the browser consumes generated data and is not an independent astronomical implementation.

Contract

Owning layer: personal
Claim kind: deterministic-fact
Time basis: Local sunrise-to-next-sunrise with UTC bisection of ascendant crossings.

Inputs

• date
• location
• sunrise
• next sunrise

Outputs

• Lagna Rashi transition windows

References and evidence

Evidence classes: astronomical
Verification states: engine_pinned

Transitions are numerically and integration tested; independent city/date comparison cells are not registered.

No registered claim ID; the provenance note below is the current disclosure.

The complete machine-readable source registry is available in provenance.json. A regression fixture or same-code reproduction is not independent verification.

Reproduce and review

• tests/test_lagna_hora.py
• tests/test_lagna_json_builder.py

Run the linked tests, then the complete offline contract:

python tools/verify_project.py

Public surfaces

• python-library
• mcp
• website
• generated-data

Limitations

• The browser mirror renders generated transitions; it does not independently recompute the ascendant.

Implementation

• owner: telugu_panchangam/personal/lagna_hora.py — get_lagna_transitions
• mirror: src/panels/today.ts — lagnaSegments

This route is generated from computations.json. Edit the registry and canonical reference prose in the same pull request as a behavior change.