Protect your eyes during the solar eclipse

The upcoming eclipse on August 12 is a unique opportunity to observe one of the greatest astronomical spectacles visible to the naked eye. But it can also be a source of serious problems if proper precautions are not taken. Here's what we need to keep in mind:

The danger of looking at the Sun

Looking directly at the Sun—whether during an eclipse or under normal conditions—can cause serious and irreversible eye damage, including blindness. The retina can burn without producing any pain, so the damage may go unnoticed at the time. This warning applies to the uneclipsed Sun as well as the partially eclipsed or annular eclipsed Sun: even 1% of the visible solar surface emits enough radiation to permanently damage the eye's light receptors.

Symptoms of solar retinopathy—the eye injury caused by sun exposure—may not be noticeable at the time but hours or even days later. These include blurred vision, visual distortion, and the appearance of a central blind spot (scotoma) that makes everyday activities such as reading difficult. In more severe cases, exposure can cause a macular hole that requires surgical intervention. Repeatedly looking for even a few seconds without protection can accumulate damage.

What glasses to use

The only glasses suitable for direct solar observation are those certified with standard EN ISO 12312-2:2015, specifically for direct solar observation. This standard is different from ISO 12312-1 (ordinary sunglasses) and is the only valid one for this purpose. The glasses must reduce visible radiation by a minimum factor of 30,000 (allowing no more than 0.0032 % of light to pass through) and effectively block both ultraviolet and infrared radiation. In addition, if they are marketed in the European Union, they must bear the CE mark, backed by laboratory tests.

How to check if glasses are safe

• The CE mark must be visible, legible, and indelible, and backed by laboratory tests, not just printed.
• Labeling must include the manufacturer's name, instructions for use, warnings, and, if applicable, an expiration date (expiration dates are 3 years after manufacture).
• Physically examine the filter: it should not have scratches, lighter areas, bends, perforations, or any defects.
• Look for the inscription "EN ISO 12312-2:2015" on the glasses, their packaging, or the instructions. If it only indicates "ISO 12312-1", they are not suitable.
• See below for the glasses recommended by Astro Telescopios for this type of observation. Here you can buy certified solar eclipse glasses and here you can buy solar filters for telescopes.
• Test them beforehand by looking at them against the light or in front of an incandescent light bulb to detect defects.

How to use them correctly

• Put them on before looking at the Sun and take them off only after looking away.
• Look briefly (a few seconds) and take breaks between observations.
• Do not use them if they are scratched, broken, perforated, bent, or deteriorated.
• Supervise correct use by children and people under your care.

When to take off your glasses, depending on the type of eclipse

Total eclipses (2026 and 2027): it is safe to take off your glasses only during the minutes of absolute totality, when the Moon covers 100% of the Sun and it becomes dark. As soon as the first ray of light appears (the "diamond ring"), you must immediately protect yourself again. It is highly recommended to keep them on at all times. In regions where the eclipse is only partial, it is never safe to observe the Sun without glasses.

Annular eclipse (2028): it is NEVER safe to look without glasses. Even at the peak of the eclipse (the "ring of fire"), the Sun still emits enough direct sunlight to damage eyesight. Glasses must be kept on at all times.

In any case, it is highly recommended to keep them on at all times while observing the Sun. It is not recommended to do so for continuous periods longer than 3 minutes, even with safe glasses. 

Filters and homemade methods: what to use

Common sunglasses, smoked glass, X-rays, CDs, photographic film, cheap binocular or telescope filters, and other homemade methods are completely inadvisable. None block radiation in the range and quantity necessary to protect the eye.

Optical instruments: extreme danger

You should never look at the Sun through binoculars, telescopes, or cameras without a professional solar filter placed at the front (objective) of the device, never behind the eyepiece. The latter is a frequent and extremely dangerous mistake: the optics concentrate light and heat in such a way that they can melt the glasses and instantly burn the eye.

Sources: National Geographic Institute