Eclipse mechanics for programmers: turning ephemeris data into a "next eclipse from here" countdown

Short summary

Building an eclipse tracker requires solving two problems: predicting when an eclipse occurs and determining visibility from a specific location. Rather than computing orbital mechanics in the browser, bake precomputed eclipse data from NASA's canon into static JSON, then use point-in-polygon ray casting to determine visibility. Cache everything with service workers to enable offline functionality, making the app reliable even with poor connectivity.

• •Use precomputed eclipse catalogs (NASA's Five Millennium Canon) rather than computing orbital mechanics in JavaScript
• •Determine visibility with point-in-polygon ray casting tests against cached GeoJSON path boundaries
• •Implement service worker caching for offline operation; use requestAnimationFrame for accurate countdown timers

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