Sources and method

This site publishes astronomical data that people will use to plan a trip and to decide when to remove protective glasses. That is why we compute it ourselves rather than copying it, and check the result against independent official sources.

How the timings are computed

Local circumstances — the five contacts, the length of totality, magnitude, obscuration and the Sun's position — are computed from the Besselian elements published by NASA for this eclipse, solved with the classical procedure in the Explanatory Supplement to the Astronomical Almanac. That yields correct data for any coordinates, not just for places somebody has tabulated.

How it is validated

The calculation is checked automatically against independently published values before every deployment: the duration at the point of greatest eclipse in Egypt per NASA, the municipal durations published by Spain's IGN for Ceuta, Tarifa, Melilla, Algeciras, La Línea, Los Barrios, San Roque, Cadiz and Malaga, and the obscuration percentage in Seville. If any check fails, the deployment stops.

At the last validation, the difference against NASA's point of greatest eclipse was one tenth of a second, and against the IGN durations, between 0 and 2 seconds for almost every location. Residual differences come from the specific reference point each source uses within a municipality and from small differences in lunar radius convention.

Honest error margins

• Length of totality: reliable to within a few seconds.
• Contact times: reliable to within a few seconds. They may differ slightly from IGN tables because of the ΔT value and lunar radius convention used.
• The real instant of C2 and C3 also depends on the terrain of the lunar limb, which adds a second or two of variation that cannot be eliminated.
• This is why the safety guide keeps repeating it: do not trust the clock to remove your filter, trust what you see.

Sources

• NASA/GSFC (Espenak & Meeus, Five Millennium Canon of Solar Eclipses) for the Besselian elements.
• Instituto Geográfico Nacional (IGN), Spain, for reference local circumstances and the description of the path across Spain.
• Junta de Andalucía for the official list of municipalities inside the path.
• AEMET for climatology and weather forecasting.
• Local councils and astronomy societies for events and designated viewing areas.

Automatic updating

A system of agents checks official sources daily and publishes verifiable updates. Astronomical data is the exception: an agent can propose a change and flag a discrepancy, but it cannot alter a contact time on its own. That change always goes through review.

Corrections

If you spot an incorrect figure in our data for Ceuta, tell us with the source and we will fix it. Significant corrections are noted on the page itself.