Halcyon is built on freely available and openly licensed data, maintained by people and organizations who deserve the credit. Thank you to all of them.
Open-Meteo — hourly forecasts from the ECMWF IFS, GFS, and ICON models, plus the Marine API for coastal detection. Open data, free for non-commercial use.
© OpenStreetMap contributors — place search and reverse geocoding via the Nominatim service.
lightpollutionmap.info by Jurij Stare — Bortle class and sky-brightness estimates derived from VIIRS satellite radiance data.
NOAA Tides & Currents for U.S. stations, and TideCheck for international locations. Tide predictions are for planning only — not for navigation.
NOAA Space Weather Prediction Center — planetary K-index forecast for aurora potential.
NOAA STAR / GOES West — Day/Night Cloud composite loops for real-time sky checks.
Summit locations for the nearby-peaks alpenglow feature come from the World Ribus dataset of global prominence peaks, used with thanks under its credit-required terms. Supplementary U.S. summit names are from the USGS Geographic Names Information System (GNIS), public domain.
Sun and moon position, phase, and rise/set times computed with SunCalc by Vladimir Agafonkin (BSD-2-Clause). Galactic-core positions derived from standard equatorial-to-horizontal transforms.
Disclaimer. Halcyon scores are model-based estimates — real skies vary, and forecasts grow less reliable further out. Always check conditions again the evening before you shoot. Halcyon is not liable for forecast errors or decisions made from them. Tide predictions are for planning only, not navigation.
Halcyon™ © 2026 Rajesh Jyothiswaran / LadyBugFarm Images. All rights reserved.