Eclipse Safety Guide

Why the partially eclipsed sun is dangerous

Even when the moon covers 99% of the sun, the remaining 1% is still thousands of times brighter than a full moon. The retina has no pain receptors, so you feel nothing while the damage happens. The injury — called solar retinopathy — burns the photoreceptor cells at the back of your eye. Symptoms (blurred central vision, a blind spot, distorted shapes) typically appear hours later, often the next morning, and can be permanent.

The danger is worst during the partial phases, because the sun looks dim enough to be tolerable but is still emitting full-intensity infrared and ultraviolet radiation. Your pupil dilates, you stare longer, and the damage accumulates. This is why every eclipse generates a wave of preventable eye injuries.

ISO 12312-2 eclipse glasses

The only certified-safe naked-eye filter is one that meets the international standard ISO 12312-2:2015. This standard requires the filter to transmit no more than 0.0032% of visible light and to block 100% of harmful UV and IR radiation. Compliant glasses look almost completely opaque indoors — if you can see anything other than a bright filament bulb through them, they are not safe for the sun.

How to verify your glasses are real

• Look for the ISO 12312-2 marking printed on the frame or packaging. Counterfeits often print the number without certification — buy from manufacturers listed by the American Astronomical Society (AAS) eclipse vendor list.
• Inspect for damage. Throw away glasses with scratches, pinholes, torn filters, or loose frames. Even a tiny scratch concentrates sunlight onto your retina.
• Check the date. Modern ISO 12312-2 filters do not "expire" if undamaged, but glasses older than 2015 may not meet the current standard.
• Test indoors first. Look at a bright lamp. You should see only the filament — nothing else in the room should be visible.

How to use them

Put the glasses on before looking up. Look at the sun, look away, then take them off only when your gaze is well clear of the sun. Never glance at the sun while the glasses are off — even for a split second to "find" it. If you wear prescription glasses, put eclipse glasses over them.

What changes during totality

Totality is the brief window when the moon completely covers the sun's bright disk. From locations along the path of totality across northern Spain on August 12, 2026, this lasts between 1 minute 45 seconds and 2 minutes 15 seconds, depending on the city.

The moment the diamond ring appears at the end of totality (a single brilliant flash where the first sliver of sun reappears), put your glasses back on immediately. From that moment forward you are looking at partial phases again, and standard solar safety rules apply.

If you are outside the path of totality (most of Spain, all of Portugal, southern France, the Balearics partially), the sun is never safe to look at without ISO 12312-2 protection. There is no "safe enough" partial eclipse — even a 99% partial eclipse will damage unprotected eyes.

Cameras, binoculars, and telescopes

Optical instruments magnify both the sun's image and its energy. Looking through unfiltered binoculars or a telescope at the partially eclipsed sun can blind you in less than a second — significantly faster than naked-eye damage.

Required: a front-mounted solar filter

Solar filters must be placed at the front (objective) end of the instrument, never at the eyepiece. Eyepiece-mounted filters can crack from focused heat and cause instant injury. Reputable manufacturers include Thousand Oaks Optical, Baader Planetarium (AstroSolar film), and Lunt. Glass filters are durable; film filters are cheaper and equally safe when handled carefully.

Smartphone and DSLR cameras

The same rule applies: a certified solar filter must cover the lens during all partial phases. The camera sensor will burn just like a retina if exposed directly to the sun. During totality, the filter comes off — exposure times of 1/500s to several seconds at f/8 capture the corona well. See our eclipse photography guide for camera settings.

Pinhole projection — the no-equipment option

If you don't have eclipse glasses, you can safely watch the partial phases by projecting the sun's image onto a flat surface. You never look at the sun directly.

• Cardboard pinhole. Punch a small hole (2–3 mm) in a piece of cardboard. Stand with your back to the sun, hold the cardboard high so sunlight passes through the hole and projects onto a second sheet held below. The image will show the sun's crescent shape during partial phases.
• Colander or kitchen strainer. Hold over a sheet of white paper. Each hole projects its own miniature crescent — dozens at once.
• Tree shadows. The gaps between leaves act as natural pinholes. Look at shadows on the ground under a leafy tree during partial phases — they will be covered with crescent shapes.
• Two index cards. Make a pinhole in one, hold it about 30 cm above the other. Adjust the distance until the projected sun image is sharp.

Watching with children

Children's enthusiasm is the highest risk factor. Their pupils dilate more than adults, their lenses transmit more UV, and they may sneak a glance "just to see." Practical guidance:

• Practise with the glasses indoors the day before. Make it a game: "look at the lamp, look away."
• Stay within arm's reach during partial phases. An adult should be able to physically intervene if a child takes off their glasses.
• For children under 5, pinhole projection is safer than glasses. Small heads slide out of adult-sized eclipse glasses and they can't reliably keep them on.
• Cover camera lenses, binocular eyepieces, and telescope eyepieces when not actively in use. Curious hands find them.

Common myths and unsafe alternatives

Sunglasses, even multiple pairs. Standard sunglasses transmit roughly 1,000 to 10,000 times more light than ISO 12312-2 glasses. Stacking them reduces brightness but not infrared, and infrared is what cooks the retina.

Smoked glass. An old recipe that has blinded people for over a century. Carbon deposits are uneven and don't block IR.

Exposed film negatives. Modern color negatives have no silver to block UV. Old black-and-white negatives could in principle work but are inconsistent and unreliable.

CDs and DVDs. Decorative reflective surfaces, not optical filters. They scratch and have pinholes.

Welder's glass. Only shade 14 or higher is safe, and most welding shops sell shade 10 or 12. If you can't verify the shade number, don't use it.

Looking through a phone screen. The phone's camera is being damaged just like your eye would be. The screen feels safe because it's a translation, but the underlying sensor is taking the hit.

"My eyes will hurt and I'll look away." They won't. There are no pain receptors in the retina. The first sign of damage is reduced vision hours later.

Pre-eclipse checklist

• Eclipse glasses bought from an AAS-listed vendor, marked ISO 12312-2, inspected for scratches
• One pair per person plus spares (they cost a few euros each)
• Solar filter for any binoculars, telescope, or camera you plan to use
• Backup pinhole projector materials (cardboard + paper) in case glasses fail
• Cloud cover forecast checked the morning of — see your city page
• Plan an unobstructed western horizon (the sun will be only 4–10° high during totality in Spain)
• Set a phone alarm for first contact (start of partial phase) and second contact (start of totality)
• Brief everyone in your group, especially children, on the rules

For the path of totality and exact local times in Spain, see our main eclipse guide. For historical context on the 1999 Europe and 2017 / 2024 US eclipses, see the eclipse history page.