Astronomical calculations
Local solar-eclipse circumstances are calculated with Astronomy Engine 2.1.19 from latitude, longitude and elevation. The result includes contact times, obscuration, local eclipse type, solar altitude and azimuth.
Event-specific searches are pinned to a known eclipse date. If that event is not locally visible, the interface says so instead of silently returning a different eclipse.
Reference cross-checks
Global paths, maximum duration and Besselian elements are checked against NASA GSFC. Spanish municipality values are compared with the Instituto Geográfico Nacional, and representative country or city values are compared with an independent published table.
Small duration differences can arise from solar-radius conventions and the exact coordinates chosen. Published destination tables therefore use authoritative cross-checks for duration and rounded model values for city-centre planning.
Historical weather context
City guides use hourly ERA5 reanalysis provided by the Open-Meteo Historical Weather API. For each city, the dataset samples 2 August in every year from 2000 to 2025 and averages the three hours around the local 2027 eclipse maximum.
The published summary includes mean and median total cloud, mean low cloud, humidity and temperature. The clear-sample rate is the share of annual three-hour samples with average total cloud at or below 20%. This threshold is a Next Eclipse Guide comparison measure, not an official forecast category.
- Reanalysis describes a model grid cell and can miss local fog, dust, smoke and terrain effects.
- Twenty-six historical dates are climate context, not a prediction for 2 August 2027.
- Event-day decisions should use current forecasts, satellite images, observations and lawful travel options.
- The generating script and versioned CSV retain the coordinates, hours, source model and sample count.
Time zones and rounding
- Interface times use the IANA time zone associated with the selected location.
- Static tables are rounded to the nearest minute and name their time zone in the downloadable data.
- Future civil-time rules can change; recheck official local time before the event.
- Near a totality boundary, calculate the exact observing coordinates rather than relying on a city label.
Viewing-location ranking
The spot finder combines eclipse coverage, solar altitude, mapped OpenStreetMap terrain type and distance. Weather is included only inside the available forecast window.
A score is a comparison aid, not proof of access, safety, capacity or a completely unobstructed horizon. Users must verify these conditions locally.
Change log
| Date | Change | Reason |
|---|---|---|
| 22 Aug 2026 | Added seven city guides, ERA5 climate dataset and versioned provenance | Direct answers and original citeable data for search and AI systems |
| 14 Aug 2026 | Added event-pinned 2027 calculations, localized pages and downloadable city data | Post-2026 rollover and reproducibility |
| 12 Aug 2026 | Added licensed 2026 photo archive | Historical coverage and image attribution |
| 8 Aug 2026 | Initial calculation verification | Launch baseline |
Sources and methodology
Dates, paths and safety guidance use the references below. Local timings are rounded calculations for the stated reference points; recalculate your exact observing location.
- NASA GSFC: Solar eclipse predictions ↗Catalogs, Besselian elements and global-path verification.
- Astronomy Engine documentation ↗Calculation model, algorithms and validation background.
- Open-Meteo Historical Weather API ↗ERA5 hourly cloud, humidity and temperature variables used by the climate dataset.
- Instituto Geográfico Nacional: 2 August 2027 eclipse ↗Official Spanish path and municipality circumstances.
- OpenStreetMap copyright and licence ↗Terrain and viewpoint data attribution.