Where is the next eclipse? Why NASA now has more accurate eclipse maps

Very few witnessed yesterday’s “ring of fire” eclipse in the southern hemisphere. But did you really experience totality on April 8, 2024? Several events advertised by ill-advised organizers as perfect for witnessing the North American total solar eclipse were slightly off the path of totality. As a result, thousands could see a 99.99% partial solar eclipse, with no dark sky and no view of the sun’s magnificent corona. Most wouldn’t know what they were missing.

For experienced eclipse watchers, however, there is a bigger problem: the official maps for the path of totality during all total solar eclipses need to be corrected. Not much, but there is enough inaccuracy for eclipse calculators to notice that something is going wrong. The reasons? The sun’s radiance and the topography of the moon and the Earth, none of which have been consistently taken into account—until now.

The path of totality

Here’s why it’s essential. Whenever a total solar eclipse occurs, eclipse chasers must enter the path of totality—a projection of the moon’s central shadow, ombra – on the surface of the Earth. Only from within that path is the sun completely obscured by the moon’s shadow for a few minutes. The difference between seeing a total solar eclipse and a partial solar eclipse is, literally, like night and day.

The unspoken truth

Eclipse watchers have known for decades that eclipse maps are wrong. The traditional method of calculating the eclipse, invented 200 years ago, assumes that all observers are at sea level on Earth, that the moon is a smooth sphere, and that the size of the sun remains constant. In practice, none of this is true.

• Earth’s topography changes drastically where the moon’s shadow falls, changing where the edge of the path of totality is.
• According to NASA, the ridges and valleys along the edge of the moon’s disk affect the timing and duration of totality by several seconds.
• The sun’s beam appears to wax and wane over unknown periods of time, so much so that a projected moon’s shadow varies in latitude.

The calculations also use something called Delta-T – the rotational speed of the Earth – which in recent years has had to be constantly updated.

None of this is widely publicized when a central total solar eclipse is about to hit. After all, the public finds these events confusing enough without adding more suspense. But for some cartographers, mathematicians and eclipse scientists, getting the most accurate maps is an obsession.

‘Grazing Areas’

The truth is that eclipse maps are mostly very accurate. The only exception—and where any of the above uncertainties cause a problem—are the edges of the path of totality. There may be a finish line on a map that marks the end of an eclipse path, but in reality, there is only a “grazing area” where no one is quite sure what will be seen or experienced.

Earth elevation tables and lunar limb plots have been used by eclipse cartographers for years, with eclipse calculations gaining greater accuracy in recent years thanks to new lunar topography data from NASA’s Lunar Reconnaissance Orbiter. s, which orbits the moon and takes measurements.

The maps available for eclipses use different values ​​for the sun’s irradiance, so a location that appears to be just inside the path of totality on some maps appears slightly outside on others.

Solar Ray and Earth

The standard value of the sun’s irradiance is 959.63 seconds of arc (one second of arc is 3600th of a degree), figures used since the late 1800s, but the sun appears to be larger, about 960 seconds arch. After eclipse modeler John Irwin discovered that the edges of the path of totality on the April 8 eclipse map would be up to 2,000 feet. (600 meters) very narrow and very wide in places, Luca Quaglia — an Australia-based eclipse calculator who has been helping determine the solar radius since 2013 — and his Besselian Team took measurements of what was seen actually on the edge of Stephenville, Texas, where some predicted the eclipse would last 60 seconds, but from Irwin it would last 15 seconds. The latter was so in practice.

The analysis compares umbral shadow path predictions with experimental data, revealing that Irwin’s maps are more accurate. “We really need to calculate the topography of the Moon and Earth and use an improved solar eclipse to closely model reality,” Luca Quaglia said in an email.

Meanwhile, NASA has been working on the Moon.

The ever-changing shadow of the moon

In a total solar eclipse, the exact shape of the moon is everything. The valleys at the edge of the moon create two of the most spectacular sights during a total solar eclipse – Baily’s beads and the diamond ring, the last parts of the sun visible just before and the first just after totality. Eclipse cartographer Michael Zeiler at GreatAmericanEclipse.com — one of the first to develop eclipse maps that include the “grazing zone” — even calculated a map showing exactly where the “double diamond rings” would be visible on the 8th april

The real moon

Now, NASA has developed the first visualizations depicting the actual, time-varying shape of the moon’s shadow, with the effects of a precise lunar limb and Earth’s terrain. “Beginning with the total solar eclipse of 2017, we have published eclipse maps and movies that show the true shape of the moon’s central shadow—the umbra,” said Ernie Wright, NASA visualizer at NASA’s Space Flight Center. s Goddard in Greenbelt, Maryland. . “People ask, why does it look like a potato instead of a smooth oval? The short answer is that the moon is not a perfectly smooth sphere.”

In a new article published earlier this month in Astronomical JournalWright determines exactly how the moon’s terrain creates the shape of its shadow. It uses elevation maps of the Moon from LRO to create a profile of the lunar limb that changes continuously as the moon’s shadow passes over Earth. However, he also used several NASA datasets to provide an elevation map of the Earth so that locations could be depicted at their actual elevation. New computer-driven technique can render eclipse maps one pixel at a time.

Projections with holes

Perhaps the most important point of Wright’s work is that he discovers that valleys on the edge of the Moon act like pinholes that project images of the sun onto the Earth’s surface. The edges of the umbra are not shown to be a straight line nor a “grazing area”, but a series of small arcs from the edges of the projected images of the sun.

It’s another great example of how modern science, using complex mathematics and 3D animation software, can reveal something new and wonderful about the natural world.

The next total solar eclipse will occur on August 12, 2026, from eastern Greenland, western Iceland and northern Spain.

I wish you clear skies and open eyes.