The Engineering Behind the Eclipse

On August 12, the sky will offer one of the most spectacular astronomical phenomena: a total solar eclipse visible from various locations in Spain. For a few minutes, the Moon will completely block out the Sun and cast its shadow over a narrow strip of the Earth.

The event raises questions related to security, the energy system, and mathematics—which make it possible to predict subject planetary movements.

Researchers at Tecnun, the University of Navarra’s School of Engineering— Xabier Insausti and Tomás Gómez-Acebo— along with Ceit researcher Ceit Tecnun professor Ainara Rodríguez, are analyzing the engineering behind the eclipse.

How to Safely View the Eclipse

Although it may seem harmless, looking directly at the Sun during an eclipse can cause serious and even irreversible damage to the retina. Ainara Rodríguez, a researcher with Ceit Precision Laser group Ceit a professor at Tecnun, explains that exhibition can cause solar retinopathy, a condition caused by the concentration of light on the retina. “Our eyes function like a magnifying glass, focusing light onto a very small point on the retina. That energy destroys tissue through two simultaneous mechanisms: photochemical damage, caused by ultraviolet (UV) radiation, and photothermal damage, caused by infrared (IR) radiation, which burns the proteins in the retinal cells,” she explains.

The researcher warns that the retina lacks pain receptors, so the injury goes unnoticed as it occurs. Symptoms, such as blurred vision, color distortion, dark spots, or blind spots, usually appear between four and twelve hours after exhibition. “In mild cases, the injury may be reversible, but when exhibition been prolonged, the damage can be permanent. “The only way to prevent this is by using eclipse-approved glasses,” she notes.

Rodríguez emphasizes that conventional sunglasses do not provide the necessary protection. Although they block virtually all ultraviolet radiation and reduce some of the visible light, they do not filter out infrared radiation. “As the eclipse progresses, visible light diminishes and the pupil dilates to maintain vision. This allows a greater amount of infrared radiation to reach the retina, which can cause severe damage,” he explains. For this reason, eclipse-specific glasses are considered personal protective equipment (PPE) and must comply rule 12312-2. “Unlike regular sunglasses, they block 100% of ultraviolet radiation, more than 97% of infrared radiation, and more than 99.99% of visible light,” he states.

The researcher also recommends taking extreme precautions when using cameras, binoculars, or telescopes. While the main risk with cell phones is that the concentrated light can damage the camera sensor, in the case of binoculars or telescopes, the danger is directed straight at the eye, since these instruments focus the light even more intensely on the retina. “The solution is always to place an approved filter in front of the camera or the lenses of the binoculars or telescopes—never behind them or on the eyepieces,” she concludes.

Mathematics for Determining the Path of an Eclipse's Shadow

How is it possible to know the exact path of an eclipse's shadow years in advance? The answer lies in the mathematical models that describe the motion of celestial bodies.

Xabier Insausti, researcher group Mathematical group Tecnun, explains that these predictions are based on the laws of celestial mechanics, which draw on analytical geometry, vector geometry, and trigonometry. “These theoretical models incorporate astronomical ephemerides (the calculated positions of the Sun, the Moon, and the Earth) and various computational mathematics methods that allow the calculations to be adjusted to reflect reality,” the expert notes.

As Insausti explains, there is a process for determining where and when an eclipse will be visible. “The calculation involves tracking, second by second, the shadow cast by the Moon in space until the exact point where it intersects the Earth’s surface is determined.” First, the positions of the Sun, the Moon, and the Earth at every instant are determined with great precision using astronomical ephemerides. Next, the Moon’s shadow is modeled as a cone emanating from the Moon, and the point where it intersects the Earth’s surface is calculated. Finally, using numerical methods, the intersection of that shadow with the Earth’s surface is adjusted moment by moment. “

"The Earth is not stationary, nor is it a perfect sphere: it rotates, is slightly flattened at the poles, and its rotation also has slight irregularities. That is why the calculations incorporate models of the Earth’s actual shape, its rotation, and the Moon’s exact position," explains the researcher professor at the School of Engineering.

Insausti adds that these models must be continuously refined using various techniques, since they simplify reality. “In applied physics, there is never a completely perfect prediction, because we always work with approximate models. What we can do is estimate the margin of uncertainty and reduce it until it is practically irrelevant for this subject ” notes the researcher the School.

When the sun goes down, energy leave also leave

The eclipse also affects electricity generation, as it causes a sudden and temporary drop in photovoltaic energy production by blocking out the sunlight. Tomás Gómez-Acebo, Full Professor Thermodynamics in department Mechanical Engineering Materials at Tecnun, explains it this way: “As the sky darkens, output from solar farms drops rapidly, only to rebound just as quickly once the sun reappears.”

In the case of August 12, the eclipse will begin on the Iberian Peninsula around 7:30 p.m., and its total phase (100% darkness) will occur between 8:26 p.m. and 8:33 p.m., depending on the geographic location. At that time of day in August, as the expert points out, the Sun will already be very low on the horizon, at about seven Degrees. “At that time, national photovoltaic production is already plenary session of the Executive Council natural plenary session of the Executive Council due to sunset, which prevents the critical scenario of a solar blackout in the middle of the day.” He also explains that the “disappearance of the sun” has certain effects on the network , as it requires the network operator—such as network in Spain—to compensate for the shortfall caused by the “unusual drop in solar energy.” 

Therefore, with the goal ensuring supply, generation is immediately increased through other backup sources, such as hydroelectric, natural gas, or combined-cycle power plants. In this regard, the researcher explains that electricity system operators prevent power outages thanks to advance planning. First, “they use predictive algorithms—that is, meteorological and astronomical models—to calculate exactly how many megawatts (MW) will no longer be produced.” Then, “they tap into energy reserves: backup plants are prepared and brought online before the eclipse begins to cover the drop in voltage without compromising the network.”