{"id":2914,"date":"2025-09-05T03:46:13","date_gmt":"2025-09-05T03:46:13","guid":{"rendered":"https:\/\/www.newsbeep.com\/nz\/2914\/"},"modified":"2025-09-05T03:46:13","modified_gmt":"2025-09-05T03:46:13","slug":"most-solar-eclipse-maps-have-a-major-flaw-heres-how-to-ensure-youre-really-in-the-path-of-totality","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/nz\/2914\/","title":{"rendered":"Most solar eclipse maps have a major flaw. Here’s how to ensure you’re really in the path of totality"},"content":{"rendered":"

Solar eclipse maps show crisp lines for the path of totality, the narrow strip where a total solar eclipse will be visible. But in reality, the edges of the path are fuzzy, jagged and sometimes wrong by hundreds of meters or more. That might not matter if you’re standing on the path’s centerline, where many eclipse chasers head to experience the longest duration of totality. However, for those at the edge of the path, discrepancies could be the difference between seeing the sun’s corona with the naked eye \u2014 one of nature’s most incredible sights \u2014 and merely witnessing a crescent sun through solar eclipse glasses<\/a>.<\/p>\n

It’s potentially a big issue for cities whose suburbs will be within the northern or southern limit of the path of totality for the Aug. 12, 2026 total solar eclipse<\/a>, such as Madrid, Bilbao, and countless small towns and villages in Spain and Iceland.<\/p>\n

Why the maps are imprecise<\/p>\n

The reason those neat lines on solar eclipse<\/a> maps don’t always match reality is that the sun’s actual size is still a matter of debate. Eclipse paths were long calculated using Besselian elements, a set of parameters that assume spherical bodies and a fixed solar radius. However, these values are outdated.<\/p>\n

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“The canonical standard solar radius we have been using for over 100 years in eclipse computation is around 696,000 kilometers [432,000 miles] or 959.63 arcseconds,” eclipse computer Luca Quaglia said June 13 at the Solar Eclipse Conference in Leuven, Belgium. That figure was initially published in 1891 by German astronomer Arthur Auwers. “But if you use that standard value, you will be off,” Quaglia said.<\/p>\n

Related: Solar eclipse sights might vary on the edge of totality<\/a><\/p>\n

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The canonical sun’s radius is 959.63 arc seconds, but it appears to be 959.95 now \u2014 meaning eclipse paths are wrong. (Image credit: NASA SDO)<\/p>\n

Quaglia’s work over the past decade during total solar eclipses, as part of the Besselian Elements Team<\/a>, suggests that the sun’s apparent size is closer to 959.95 arc seconds, plus or minus 0.05. That’s a difference of just 0.3 arc seconds \u2014 less than one-thousandth of a degree. That may sound nitpicky. Yet, on the ground, it shifts the edge of the path of totality by up to 2,000 feet (600 meters). It’s a tiny problem with big consequences for communities on the edge of a path of totality.<\/p>\n

Going to the edge<\/p>\n

To test and retest that new figure for the solar radius, Quaglia and his colleagues don’t bask in maximum totality at the centerline during total solar eclipses \u2014 they go to the edge. By timing the second and third contacts \u2014 the moments when the photosphere (the visible surface of the sun) disappears and reappears \u2014 with GPS-time-stamped flash spectrum data from frames of video, Quaglia and colleagues can directly test which radius value matches reality. Key to that is the appearance of Baily’s beads<\/a> \u2014 the last and first drops of sunlight streaming through valleys on the moon \u2014 that signal the beginning and end of totality.<\/p>\n

Breaking space news, the latest updates on rocket launches, skywatching events and more!<\/p>\n

“Flash spectra are absolutely accurate because they can show you exactly the instant when a Baily’s bead appeared or disappeared,” Dan McGlaun, an eclipse cartographer who uses the new solar radius of 959.95 arc seconds in his eclipse maps<\/a> (as does Michael Zeiler<\/a>), told Space.com. “You can use that to back-calculate what the Besselian elements would have had to have been at that location for the beads to disappear at that time, including the radius of the sun. It’s trigonometry.”<\/p>\n

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The northern suburbs of Madrid are in the path of totality, but on this new map, there’s a “zone of uncertainty.” (Image credit: Besselian Elements\/www.besselianelements.com<\/a>)The “zone of uncertainty”<\/p>\n

Quaglia and colleagues collected their data from a point just outside the edge of the path \u2014 as predicted using other measurements of the solar radius \u2014 in Stephenville, Texas, on April 8, 2024. Even before that eclipse, Quaglia, working with mathematician John Irwin, had already packaged the math to give new, more accurate local circumstances. Most recently, they’ve produced special new eclipse maps for Spain for Aug. 12, 2026<\/a>, that diverge from other publicly available maps.<\/p>\n

These new maps replace the precise-looking line that marks the limits of the path of totality with a “zone of uncertainty” at the edge. That’s partly because, in addition to being uncertain, the sun’s radius is not sharp. In reality, the sun’s photosphere \u2014 its bright face \u2014 has fuzzy edges that fade into the chromosphere and corona.<\/p>\n

“The photosphere is not a solid object,” Quaglia said. That accounts for the plus-or-minus 0.05-arc-second error bar on any calculation of the solar radius.<\/p>\n

That means observers a few hundred meters outside the limits of any calculated path of totality may still glimpse the corona \u2014 or not. This “coronality” \u2014 the chance of glimpsing the solar corona just outside the path of totality \u2014 is unpredictable. It’s impossible to determine how far outside the eclipse limits the solar corona will cease to be visible.<\/p>\n

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Clickable eclipse maps contain a list of contact times that are based on Besselian elements. (Image credit: Xavier Jubier\/Map data: \u00a9 2025 Google Imagery, \u00a9 2025 NASA)The shape of the moon<\/p>\n

The moon<\/a> also introduces uncertainties. During a total solar eclipse, the path of totality is the projected dark shadow (umbra) of the moon. Traditional maps assume a smooth lunar limb, but valleys and mountains let sunlight leak through as beads. Using the true jagged profile, revealed in detail by NASA’s Lunar Reconnaissance Orbiter<\/a> since 2009, can shift eclipse timing by up to 3 miles (5 km).<\/p>\n

“We need to account for the moon’s complex, jagged shape as accurately as possible if we want to get the most accurate internal contact time predictions,” Quaglia said. 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.<\/p>\n

Making 3D eclipse maps<\/p>\n

Another issue is that eclipse maps are flat, but the real Earth<\/a> isn’t, with mountains and valleys blocking or extending visibility. That’s why Irwin has pioneered a new 3D computational method that accounts for not only the sun’s radius and the moon’s topography but also \u2014 uniquely \u2014 Earth’s terrain. It’s all packaged into an algorithm called Improved Quick Prediction, which powers the new maps and an upcoming Eclipse Countdown<\/a> smartphone app.<\/p>\n

The team’s eclipse map for Aug. 12, 2026, is different from others. It features jagged edges and even gaps where the mountainous terrain alters the view. Sections of the limit hug mountain ridges, sometimes even leaping over peaks where the shadow can’t reach. That’s the reality eclipse chasers must face, Quaglia said \u2014 no single line on a map can guarantee what you’ll see.<\/p>\n

“We believe these are the most accurate contact times you can compute nowadays by including all the vectors that some other predictions don’t include,” he said.<\/p>\n

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\"A\n<\/p>\n

The northern limit of the path of totality for the April 8, 2024, total solar eclipse for Stephenville, Texas, as predicted by different online maps. (Image credit: Besselian Elements www.besselianelements.com)A variable star and Earth’s changing rotation<\/p>\n

Precision in astronomy is everything, but when it comes to the sun<\/a>, it will always be somewhat elusive. The sun is a variable star. Its magnetic activity waxes and wanes across the 11-year solar cycle<\/a>, with the effect on the solar radius thought to be tens of milliarc seconds.<\/p>\n

“It’s why it would be great if this experiment was done at future eclipses<\/a>, maybe over a whole solar cycle,” Quaglia said. “That would be the only way to see any variability.”<\/p>\n

Another issue for eclipse cartographers is delta T<\/a>. Even if the exact position, width and shape of the moon’s shadow are known, exactly where it strikes Earth depends not only on its terrain but also on how fast it rotates.<\/p>\n

“The rotation of the Earth can change even though the shadow is the same,” McGlaun said. “Even a tenth of a second can change where on Earth the shadow hits.” Although it’s known that Earth’s rotational speed<\/a> does change by milliseconds, we don’t know what that figure is until it’s measured by the International Earth Rotation and Reference Systems group’s atomic clocks in Paris.<\/p>\n

The math is complex, uncertain and evolving. For anyone living close to the limits of a path of totality during a total solar eclipse, the message is simple: Head a mile or two in the direction of the centerline, and a glorious moment of totality is guaranteed under clear skies.<\/p>\n","protected":false},"excerpt":{"rendered":"Solar eclipse maps show crisp lines for the path of totality, the narrow strip where a total solar…\n","protected":false},"author":2,"featured_media":2915,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[111,139,69,147,392],"class_list":["post-2914","post","type-post","status-publish","format-standard","has-post-thumbnail","category-space","tag-new-zealand","tag-newzealand","tag-nz","tag-science","tag-space"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/2914","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=2914"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/2914\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/2915"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=2914"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=2914"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=2914"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}