Key point: Many public solar-eclipse maps rely on older Besselian inputs and an assumed solar radius that recent measurements suggest is slightly larger. That small angular difference (about 959.63 vs ~959.95 arc seconds, uncertainty ±0.05) can shift the path of totality by roughly 2,000 feet — enough to miss totality. Luca Quaglia and his team produce revised maps with a "zone of uncertainty" and, with John Irwin, are building 3D models that account for terrain. Use updated maps (for example via the Eclipse Countdown app) and certified eclipse glasses for the August 2026 event.
Most Solar Eclipse Maps Are Off — How to Track the True Path and Not Miss Totality
Key point: Many public solar-eclipse maps rely on older Besselian inputs and an assumed solar radius that recent measurements suggest is slightly larger. That small angular difference (about 959.63 vs ~959.95 arc seconds, uncertainty ±0.05) can shift the path of totality by roughly 2,000 feet — enough to miss totality. Luca Quaglia and his team produce revised maps with a "zone of uncertainty" and, with John Irwin, are building 3D models that account for terrain. Use updated maps (for example via the Eclipse Countdown app) and certified eclipse glasses for the August 2026 event.
20:52, 09.11.2025Science
Why many eclipse maps are imprecise
Watching a total solar eclipse requires being in a very narrow band on Earth called the path of totality. Many commonly distributed eclipse maps use classical Besselian elements and long-standing input values that assume a fixed solar radius. Some of those inputs are out of date, so the predicted ground tracks can be off by significant amounts for observers on the ground.
Small numbers, big consequences
Published tables often use a solar radius of about 959.63 arc seconds, while more recent estimates cluster near 959.95 arc seconds (with uncertainties on the order of ±0.05 arc seconds in some reports). That tiny angular difference translates to shifts in the central line of totality on the order of roughly 2,000 feet (several hundred meters) at Earth’s surface — easily the difference between seeing full totality and missing it entirely.
Field measurements and improved maps
Luca Quaglia and his team (referred to in the original reporting as the Basselian Elements Team) have spent more than a decade measuring eclipse edges in the field. By deploying precise instruments along predicted margins, they record where the Moon’s shadow actually falls and use those observations to refine the effective solar radius and correct map traces. Their maps now include a clear "zone of uncertainty," a realistic band showing where observers have the best chance of seeing totality rather than a single thin centerline.
Accounting for real terrain: 3D modeling
Quaglia is collaborating with mathematician John Irwin to build three-dimensional computational models that incorporate surface topography — mountains, valleys and other elevation changes — instead of assuming a flat Earth projection. Because local peaks and depressions can slightly alter timing and geometry at a given site, incorporating elevation data produces a more accurate, location-specific path for the Moon’s shadow. These refined products are distributed through the Eclipse Countdown mobile app.
Practical planning tips
- Use updated maps that show a zone of uncertainty rather than a single centerline when planning a viewing site.
- Factor in local topography — a valley or ridge can matter near the edge of totality.
- Allow extra margin when choosing a site (arrive early, plan alternate sites along the band).
- Verify your eclipse glasses are certified and undamaged before the event; they are essential during partial phases.
Note: The next total solar eclipse mentioned in the article occurs in August 2026. With improved maps and some planning, you can greatly increase your chances of witnessing true totality.
Sources and tools: Besselian elements (classical formulation), field measurements by Quaglia's team, 3D terrain-aware modeling by Quaglia and John Irwin, and the Eclipse Countdown app for updated maps and tools.