74b6f609f8
* add Forgejo CI mirror and telemetry disclosure Mirrors .github/workflows/ci.yml to .forgejo/workflows/ for self-hosted runner on git.ariccamarata.com. Adds failure-reporting hook stub (server registration via nself sentry ci enable is a server-side step). Adds telemetry disclosure section to README. * add opt-in telemetry via @acamarata/telemetry (off by default) * chore: update lockfile for @acamarata/telemetry devDep * chore: fix prettier formatting on telemetry import
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nrel-spa
Pure JavaScript implementation of the NREL Solar Position Algorithm (SPA). Computes solar zenith angle, azimuth, sunrise, sunset, and solar noon for any location and date. Zero dependencies, synchronous. Validated to produce identical results to the original NREL C reference implementation.
Installation
npm install nrel-spa
Quick Start
import { getSpa, calcSpa } from 'nrel-spa';
const date = new Date('2025-06-21T00:00:00Z');
// Raw fractional hours
const raw = getSpa(date, 40.7128, -74.006, -4); // New York, EDT
console.log(raw.sunrise); // 5.417
console.log(raw.solarNoon); // 12.965
console.log(raw.sunset); // 20.509
// Formatted HH:MM:SS strings
const fmt = calcSpa(date, 40.7128, -74.006, -4);
console.log(fmt.sunrise); // "05:25:03"
console.log(fmt.solarNoon); // "12:57:56"
console.log(fmt.sunset); // "20:30:35"
CommonJS:
const { getSpa } = require('nrel-spa');
Pass a zenith angles array as the sixth argument to getSpa/calcSpa for civil (96°), nautical (102°), or astronomical (108°) twilight times.
TypeScript
import { getSpa, calcSpa, formatTime, SPA_ZA_RTS } from 'nrel-spa';
import type { SpaOptions, SpaResult, SpaFunctionCode } from 'nrel-spa';
Documentation
Full API reference, algorithm notes, and twilight calculation guide: GitHub Wiki
Related
- solar-spa: WASM build of the same algorithm, async, for high-throughput batch work
- pray-calc: Islamic prayer times built on nrel-spa
Acknowledgments
The core algorithm is a JavaScript port of the NREL SPA by Ibrahim Reda and Afshin Andreas:
Reda, I., Andreas, A. (2004). "Solar Position Algorithm for Solar Radiation Applications." Solar Energy, 76(5), 577-589.
License
MIT (TypeScript wrapper and build tooling). The core algorithm in lib/spa.js is a port of NREL's SPA C source, subject to its own terms. See LICENSE.
Telemetry
This package supports optional, anonymous usage telemetry via @acamarata/telemetry. It is off by default. See TELEMETRY.md for what is collected and how to enable or disable it.