The upcoming eclipse on August 12, which will be visible across a large part of our country, is a unique opportunity to witness one of the greatest astronomical spectacles visible to the naked eye. But it can also cause serious problems if proper precautions aren’t 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 damage to your eyesight, including blindness. The retina can be burned without causing any pain, so the damage may go unnoticed at the time. This warning applies to the Sun during a total eclipse as well as to the Sun during a partial or annular eclipse: even the 1% of the Sun’s surface that remains visible emits enough radiation to permanently damage the eye’s light-sensitive cells.

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

What glasses to wear

The only sunglasses suitable for direct solar observation are those certified to the EN ISO 12312-2:2015 standard, which is specifically designed for direct solar observation. This standard is different from ISO 12312-1 (ordinary sunglasses) and is the only one valid for this purpose. The glasses must reduce visible radiation by a factor of at least 30,000 (allowing a maximum of 0.0032% of light to pass through) and effectively block both ultraviolet and infrared radiation. Additionally, if they are sold in the European Union, they must bear the CE marking, backed by laboratory testing.

How to Check If Your Glasses Are Safe

• The CE marking must be visible, legible, and indelible, and must be supported by laboratory testing—not merely printed.
• The label must include the manufacturer's name, instructions for use, warnings, and, if applicable, the expiration date.
• Visually inspect the filter: it should not have any scratches, lighter areas, creases, holes, or defects of any kind.
• Look for the marking “EN ISO 12312-2:2015” on the glasses, their packaging, or the instructions. If it only says “ISO 12312-1,” they are not suitable.
• Check reliable sources such as planetariums or astronomy associations to find recommended retailers. You can visit these reliable websites here and here to purchase them.
• First, hold them up to the light or in front of an incandescent light bulb to check for defects.

How to Use Them Correctly

• Put them on before looking at the sun, and take them off only after looking away.
• Look briefly (for a few seconds) and take breaks between observations.
• Do not use them if they are scratched, broken, punctured, bent, or damaged.
• Make sure children and those in your care use it properly.

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

Total eclipses (2026 and 2027): It is safe to remove your eclipse glasses only during the minutes of 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 put your glasses back on immediately. It is best to keep them on at all times.

Annular eclipse (2028): It is NEVER safe to look at the sun without special viewing glasses. Even at the peak of the eclipse (the “ring of fire”), the sun still emits enough direct sunlight to damage your eyes. You must keep your viewing glasses on at all times.

Homemade filters and methods: what to use

Ordinary sunglasses, tinted lenses, X-rays, CDs, photographic film, cheap filters for binoculars or telescopes, and other homemade methods are strongly discouraged. None of them block radiation in the range and quantity necessary to protect the eye. The only relatively acceptable homemade method, though with optical limitations, is high-grade (12 to 14) welder’s glass or filter. However, the safest method for anyone remains observation via projection.

Projection observation: the safest method

The safest option, especially for children and groups, is to project the image of the Sun onto a surface rather than looking at it directly. There are several techniques:

• Two pieces of cardboard with a hole. A small hole is cut into a piece of opaque cardboard, and light passing through it is projected onto the second piece of cardboard, which serves as a screen. The size of the hole and the distance between the two pieces of cardboard affect the sharpness and brightness of the image.
• Mirror with a hole. A handheld mirror covered with paper that has a half-centimeter hole cut out of it projects an image of the Sun onto a wall or ceiling. It allows several people to observe it at the same time.
• Binoculars or a telescope (for projection only). They produce a brighter, sharper image, but require additional precautions: the device must be allowed to cool down periodically, and no one should look through the eyepiece. The screen should be placed on the floor, perpendicular to the beam of light.
• Nature. Tree leaves act as tiny pinhole cameras, projecting hundreds of crescent-shaped images of the Sun (or the eclipse) onto the ground.

Optical instruments: extreme danger

You should never look at the Sun through binoculars, telescopes, or cameras without a professional solar filter attached to the front (lens) of the device—never behind the eyepiece. The latter is a common and extremely dangerous mistake: the optics concentrate light and heat to such an extent that they can melt the eyepiece and instantly burn your eye.

Sources: Instituto Geográfico Nacional and official website Trío de Eclipses.