Question 1

What is Moira and how is it different from other Python astrology libraries?

Accepted Answer

Moira is an astronomy-first Python library for astrological computation. Unlike Kerykeion and Immanuel, which are thin wrappers around the Swiss Ephemeris C binary, Moira exposes the full reduction pipeline as inspectable Python functions — from raw JPL SPICE kernel reads through light-time correction, relativistic deflection, precession, nutation, aberration, and topocentric parallax. Every intermediate value is accessible, modifiable, and validatable. This makes Moira suitable for research, peer review, and any application where reproducibility and auditability matter.

Question 2

What ephemeris does Moira use, and why does it matter?

Accepted Answer

Moira is built on JPL DE441 — NASA's most accurate planetary ephemeris, covering the full solar system from 13,200 BCE to 17,191 CE. Moira reads DE441 using its own native C++ DAF/SPK reader, which means positions are computed directly from the same authoritative source used by professional astronomers and space missions. Documented residuals against SOFA/ERFA are 0.00048 arcseconds for fixed stars over the J1000–J3000 range.

Question 3

Can I use Moira commercially? What is the license?

Accepted Answer

Yes. Moira is released under the MIT License, which allows unrestricted commercial use, modification, and distribution with no royalty or attribution requirement beyond preserving the license notice. This is a deliberate contrast with Swiss Ephemeris, which requires either AGPL-3.0 or a paid commercial license. With Moira, there is no licensing friction for commercial products.

Question 4

Does Moira support Vedic / sidereal astrology?

Accepted Answer

Yes. Moira supports 12 ayanamsha systems: Lahiri (the Indian government standard), Krishnamurti, Fagan-Bradley, Raman, Yukteshwar, Djwhal Khul, True Chitrapaksha, De Luce, Aldebaran (15 Tau), True Revati, True Pushya, and True Mula. The Vedic predictive engine includes Vimshottari Dasha, 27 Nakshatras, and Varshaphal (annual return). All sidereal calculations use the same JPL DE441 foundation as the tropical calculations.

Question 5

How does Moira handle asteroids and minor planets?

Accepted Answer

Moira supports 887,000+ minor planets via user-supplied JPL .bsp kernel files. Classical asteroids (Ceres, Pallas, Juno, Vesta, Chiron, Eris, Sedna, and more), Centaurs, and Trans-Neptunians are bundled. Asteroid positions go through the same full reduction pipeline as planets — light-time correction, gravitational deflection, aberration, topocentric parallax — with all intermediate stages accessible.

Question 6

What predictive techniques does Moira support?

Accepted Answer

Moira's predictive engine covers secondary progressions, tertiary progressions, minor progressions, solar arc directions, primary directions (Placidus semi-arc and mundane), solar returns, lunar returns, planet returns, transits with configurable step cadence and bisection precision, ingress detection, Firdaria, Zodiacal Releasing, and Vimshottari Dasha.

Question 7

Is the free chart calculator really free? Do I need to create an account?

Accepted Answer

Yes — completely free, no account required, no credit card, no usage limits. The free calculator is powered by the same Moira engine as the Python library and the paid workspace, using the JPL DE440 ephemeris (the professional workspace uses the full-span JPL DE441). You get a full natal chart with house cusps, planetary positions, and aspects. Chiron is included by default and additional asteroids can be added on demand. Creating an account lets you save charts and access synastry, but it is entirely optional.

Question 8

What house systems are available in the calculator?

Accepted Answer

The free calculator supports five house systems: Placidus, Koch, Whole Sign, Equal House, and Regiomontanus. The default is Placidus. The full Moira engine supports 22+ house systems, available in the Workspace and via the Python library.

Question 9

What does the Moira Workspace include that the free calculator doesn't?

Accepted Answer

The Workspace adds: full natal, transit, and synastry chart calculations with 70+ celestial bodies (planets, asteroids, TNOs); all major house systems; Vedic ayanamsa support (Lahiri, Raman, Krishnamurti, and more); topocentric precision via the JPL DE441 kernel; aspect orb customisation per body class; stations and phenomena lookup; the full fixed star catalogue; and unlimited chart sessions with no rate limits. It is a professional browser-based environment for practitioners and researchers.

Question 10

How much does the Moira Workspace cost?

Accepted Answer

The Workspace is $19/month or $190/year (equivalent to $15.83/month — two months free on the annual plan). During the current beta period, a coupon code is available at checkout. There is no per-seat or per-chart fee; one subscription covers unlimited usage.

Question 11

How does Moira compare to Swiss Ephemeris in accuracy?

Accepted Answer

Swiss Ephemeris is a mature, well-validated library and Moira does not claim to supersede it on raw precision for standard planetary positions. The key difference is in the source of truth and the computation model. Swiss Ephemeris uses Astrodienst's own bundled files; Moira reads JPL DE441 directly. For fixed stars, Moira achieves 0.00048 arcsecond residuals against SOFA/ERFA over the J1000–J3000 range. The practical advantage of Moira is inspectability, MIT licensing, and the breadth of built-in techniques.

Question 12

Is there a REST API available for developers who don't want to use Python?

Accepted Answer

Yes. The Moira REST API exposes all major calculation endpoints — natal charts, houses, synastry, progressions, transits, returns, fixed stars, asteroids, and more — over HTTP with JSON responses and full OpenAPI documentation. It is language-agnostic and can be called from any environment that can make HTTP requests.

Metric	Measured value	Notes
Supra-critical Swiss fixture cases	`936`	Filtered from the cached `t.exp` house fixture
Latitude samples	`+89.9 deg`, `-89.9 deg`	Both polar extremes are present
JD range	`2456334.5` to `2456335.4166666665`	2013 polar slice in the fixture
Supported systems represented	`13`	`O`, `R`, `C`, `E`, `V`, `W`, `X`, `H`, `T`, `B`, `M`, `U`, `Y`
Failures above `0.001 deg`	`0`	Same threshold as the main Swiss house validation

Polar House External Reference

Polar House External Reference

Purpose

What the oracle covers

System names represented

What this proves

What this does not prove

Proof artifact