Use special eclipse glasses to prevent eye damage
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Viewing a total solar eclipse is an experience that can stay with you for life, but, without the proper precautions, that could be for all the wrong reasons. Looking directly towards the sun is dangerous, so read on for how to view an eclipse safely and what you need to organise in advance.
On 8 April 2024, a total solar eclipse will be visible to over 42 million people across North America. The path of totality is only about 185 kilometres wide, touching parts of Mexico, 13 US states and Canada. Most people in North America will experience this event not as a total solar eclipse but as a partial.
“For those outside the path of totality, the moon will never fully cover the sun,” says Jeff Todd at Prevent Blindness, an eyecare advocacy group based in Chicago. Regardless of your vantage point, eye protection is essential.
“To avoid damaging your eyes, you need to wear eclipse glasses for the entire duration of the eclipse,” says Todd. Otherwise, you risk burning your retinas. Nicknamed “eclipse blindness”, this can happen without you feeling any pain and it can be permanent. It can take days after viewing the solar eclipse to realise anything is wrong. Sunglasses don’t provide adequate protection. However, it is perfectly safe to hold eclipse glasses over prescription glasses.
How to view the eclipse safely
For those who travel into the path of totality, the prize is a naked-eye view of the sun’s corona. However, it is only visible during the brief few minutes of totality. At all other times, the partial phases will be visible, which must be observed through eclipse glasses. Todd says that those inside the path of totality also need to wear eclipse glasses at all times except during totality, the short period when the sun is totally eclipsed by the moon and it gets dark. “Only then can you remove your eclipse glasses,” he said.
It is important that people inside the path of totality use their naked eyes to view the totally eclipsed sun. “You have to look without a protective filter, otherwise you will see nothing,” says Ralph Chou at the University of Waterloo, Canada.
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Just before the end of totality, light from the sun’s photosphere will stream between the mountains and valleys on the moon. Called Baily’s beads, they will appear for a few seconds and eventually become a “diamond ring” that flashes, revealing enough of the sun’s photosphere for daylight to return. “They provide plenty of warning that it is time to resume looking at the partial eclipse with a protective filter,” said Chou.
Which eclipse glasses should I get?
It is crucial to wear eclipse glasses that meet the ISO 12312-2 international standard, which applies to products intended to be used for direct viewing of the sun. “Look for ISO standard labelling and purchase your glasses from a trusted source,” says Todd. “Get your glasses early to ensure that you have them in time for the eclipse.” Before making a purchase, check that the company or brand is on the American Astronomical Society’s vetted list of suppliers and resellers.
Eclipse glasses must not be used with binoculars and telescopes. If you want to use these devices to view a solar eclipse, they must have a solar filter over their objective lens – the lens at the other end to the one you look through. You should never put solar filters or eclipse glasses between the eye and the eyepiece of a telescope or the eyecups of binoculars.
Other safe ways of viewing the eclipse include a pinhole projector – a simple device that projects the sun’s image through a small hole onto a piece of paper or cardboard. An even easier way is to make use of the well-defined small holes in a colander or spaghetti spoon, which will project small crescent suns onto any surface.
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