Solar eclipse maps often contain an oversight. Here's how to confirm your location falls within the genuine path of totality.

The upcoming total solar eclipse on August 12, 2026, is causing excitement among astronomers and enthusiasts alike. However, a new understanding of the eclipse's path of totality reveals that it may not be as precise as previously thought.

The sun, a variable star, has a radius that changes due to its magnetic activity across the 11-year solar cycle. This variation can account for an error of up to 0.05-arc-second in any calculation of the solar radius. The sun's actual size is still a matter of debate, with a standard value of around 696,000 kilometers or 959.63 arcseconds, but recent calculations suggest a more accurate figure of 959.95 arc seconds.

This variability in the sun's size, combined with the moon's true jagged profile, revealed by NASA's Lunar Reconnaissance Orbiter since 2009, and Earth's terrain, can result in significant deviations in the eclipse's path. Calculations that use a smooth lunar limb can result in path limits that are up to 3 miles different from those calculated using the true limb.

These factors contribute to the fuzzy edges of the eclipse's path of totality, with sections hugging mountain ridges and sometimes leaping over peaks where the shadow can't reach. The path is not precise and may be off by hundreds of meters or more.

The message for anyone living close to the limits of a path of totality during a total solar eclipse is to head a mile or two in the direction of the centerline, and a glorious moment of totality is guaranteed under clear skies. Observers a few hundred meters outside the limits of any calculated path of totality may still glimpse the corona, but the exact location where the solar corona will cease to be visible is unpredictable.

To account for these uncertainties, new 3D computational methods, such as Improved Quick Prediction, are being developed. These methods take into account the sun's radius, the moon's topography, and Earth's terrain in eclipse maps. For instance, Luca Quaglia, a member of the Besselian Elements Team, goes to the edge of the path during total solar eclipses to test and retest the new solar radius value using GPS-time-stamped flash spectrum data and the appearance of Baily's beads.

Special new eclipse maps for Spain for Aug. 12, 2026, produced by Quaglia and colleagues, replace the precise-looking line that marks the limits of the path of totality with a "zone of uncertainty" at the edge. The new eclipse map for Aug. 12, 2026, features jagged edges and gaps where the mountainous terrain alters the view.

The term used for the chance of glimpsing the solar corona just outside the path of totality is "coronality". The rotation of the Earth can change the location where the solar eclipse shadow hits Earth, even by a tenth of a second, adding another layer of complexity to predicting the eclipse's path.

Despite these challenges, the total solar eclipse on August 12, 2026, promises to be a spectacular event, with its unpredictable edges adding an element of excitement for those who will witness it.