Solar Eclipse on 12 August: safe observation is the priority

On 12 August, mainland Portugal will witness a partial solar eclipse. Although only a small area of the Bragança district will experience an almost complete obscuration of the Sun’s disc, the phenomenon will be visible throughout mainland Portugal and is expected to attract the attention of thousands of people. However, there is one aspect that must not be overlooked: safety.

“Looking directly at the Sun without adequate protection can cause severe and irreversible damage to the retina,” warns Rui Agostinho, astrophysicist, one of Portugal’s leading figures in the public communication of Astronomy and Retired Full Professor at the Faculty of Sciences (Ciências ULisboa). At a time when many people are preparing to observe the phenomenon, the researcher stresses that “this is a public health issue”.

In fact, the risk is greater precisely during an eclipse. At first glance, this may seem contradictory. After all, if the Moon covers part of the Sun, does that not make it safer to look at it? The answer is no.

“During an eclipse, the reduction in brightness creates the illusion that it is safe to look directly at the Sun. That is precisely the danger,” explains Rui Agostinho. Under normal circumstances, the intensity of sunlight causes us to look away immediately. However, during an eclipse, this discomfort is reduced, leading many people to prolong their observation without protection. The problem is that harmful radiation continues to reach the retina. Even more concerning is the fact that there is no pain.

The injuries caused by direct observation of the Sun are painless at the moment they occur. The first symptoms may only become apparent the following day, when dark spots, blurred areas or partial loss of vision begin to appear as a result of retinal burns.

The recommendation is clear: direct observation of the eclipse should only be undertaken using certified solar viewing glasses or filters specifically designed for this purpose. “These filters block ultraviolet and infrared radiation, allowing only a very small fraction of visible light to pass through,” explains Rui Agostinho.

Contrary to some deeply rooted misconceptions, neither old X-ray films, nor darkened glass, nor smoked glass provide sufficient protection. “It is a very good way to damage your eyesight,” says the researcher, referring to some of the methods that continue to be passed down from generation to generation. Welding filters are only safe if they are shade 14. Any lower rating does not provide adequate protection for prolonged observation.

Myths Worth Debunking

Despite the awareness campaigns conducted during previous eclipses, many myths persist. “Some people say: ‘When I was young, I watched an eclipse through an X-ray film and nothing happened.’ The problem is that such isolated experiences create a false sense of security,” explains Rui Agostinho. The astrophysicist notes that a brief glance at the Sun is unlikely to have the same impact as prolonged observation, but warns of the risk of the message being misunderstood. “If I say that one second will do no harm, that second can easily turn into half an hour. People are left only with the idea that it is safe.”

This is precisely why experts advise against using improvised solutions. Children and people with retinal conditions require particular care. According to Rui Agostinho, the retinas of younger people allow more light to pass through than those of adults, increasing the risk of injury. For this reason, observation should always be supervised by an adult and carried out only with appropriate protection. People with retinal diseases, such as certain retinopathies, or those taking medication that increases ocular sensitivity should also avoid looking directly at the Sun.

The risk increases during holidays and at the beach

The eclipse will take place in the middle of August, when thousands of Portuguese people will be on holiday. For Rui Agostinho, this increases concern. Unlike previous eclipses, this one will occur outside the school term, reducing the impact of the usual awareness campaigns aimed at pupils and their families. In addition, the beach is one of the highest-risk environments. With a completely unobstructed horizon and the Sun above the sea, many people are likely to look up automatically to follow the phenomenon, often without having protective glasses with them.

Although many of the glasses distributed free of charge have already run out, they are still available for purchase from a variety of retailers. For Rui Agostinho, buying them can be seen as an investment. “We will have solar eclipses with a high percentage of obscuration visible from Portugal in 2026, 2027 and 2028. If the glasses are properly cared for, they can be used again.”

Considering the sheer volume of information circulating on social media, Rui Agostinho advises people to rely only on credible scientific sources. Comprehensive information on the safe observation of solar eclipses, including the various observation methods and recommended equipment, is available on the Astrodica – How to observe the Sun of the Lisbon Astronomical Observatory, at oal.ul.pt.
More important than witnessing a rare astronomical phenomenon is doing so without putting your eyesight at risk.