@astrologer/ephemera

A pocket-sized, MIT-licensed ephemeris for astrology and astronomy. JPL-grade planetary positions, houses, ayanamsas, eclipses, fixed stars and 1,000+ asteroids, in a 49 KB WebAssembly core with no dependencies. It works in Node 18+, browsers and bundlers.

• Tiny: 49 KB core plus 145 KB of planetary data, built in by default.
• Accurate: within 0.6″ of NASA JPL's DE440 over 1550–2650, or 0.03″ with the high-precision tables.
• MIT licensed: use it in closed-source and commercial apps.
• Complete for astrology: 14 house systems, 42 ayanamsas, nodes and Lilith, Uranian points, eclipses, returns and stations, sidereal returns, planetary nodes and apsides, and 411 fixed stars.
• Independently verified against JPL, NASA's eclipse canon and India's official ephemeris. See the accuracy page.

import { createEphemera, Body, HouseSystem, Ayanamsa } from '@astrologer/ephemera';

const eph = await createEphemera();                 // 1" data built in
const jd = eph.julianDate(2026, 1, 1.5);           // UT
const moon = eph.position(Body.Moon, jd);          // degrees, AU, per day
const cusps = eph.houses(jd, -0.1278, 51.5074, HouseSystem.Placidus);
const lahiri = eph.ayanamsa(Ayanamsa.Lahiri, eph.utToTt(jd, 2026));

Angles are in degrees and times are Julian days, UT or TT as each method's name says. Besides positions, houses (housesInfo also reports the polar fallback to Porphyry), ayanamsas, searches, eclipses and stars (starCount, starName, ...), there are the time and frame helpers: utcToJd, calendarDate, ttToUt, siderealTime, equationOfTime, nutation, eclipticToEquatorial (declination for parallels), heliocentric, midpoint and splitLongitude. For sidereal returns and ingresses pass { ayanamsa: Ayanamsa.Lahiri } (or a custom { jdT0, valueAtT0 }) to longitudeCrossing or heliocentricCrossing. index.d.ts documents them all.

Modules and data

createEphemera({ module, data }) picks a WebAssembly module and adds data files from the package:

| module | Size (brotli) | Data built in | |---|---|---| | '1as' (default) | 162 KB | 1" series, 1550–2650 | | '1as-chiron' | 217 KB | the same plus Chiron | | 'core' | 49 KB | none: pass data | | 'lite' | 42 KB | none; no eclipses or fixed stars |

The data names are '1as', '01as' (~0.2"), 'chiron', '1as-chiron', '01as-chiron', 'asteroids' (Ceres–Vesta and Chiron) and 'stars'. Raw bytes work too, e.g. a DE440 table (~0.002") from the repository's data/de440/:

const eph = await createEphemera({ module: 'core', data: ['01as', 'stars', tableBytes] });

Minor planets

More asteroids, centaurs and TNOs (1900–2100, ~0.5″) come in two optional files from the repository, not in this package:

• eph-minor.bin, 180 popular bodies, 5.7 MB;
• eph-minor-1000.bin, numbered 1–1000, 17 MB.

const url = 'https://raw.githubusercontent.com/intellecat/ephemera/main/data/eph-minor.bin';
const minor = new Uint8Array(await (await fetch(url)).arrayBuffer());
const eph = await createEphemera({ data: [minor] });
const eros = eph.minorBody('Eros');          // or '433', '433 Eros'
const pos = eph.position(eros, jd);

In a browser without a bundler, serve the package directory and createEphemera() fetches the files next to index.mjs. demo.html is a small example page.

More

The C library, the accuracy figures, the methods and the references are in the main repository: https://github.com/intellecat/ephemera. License: MIT.