How to safely view an eclipse

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 (Image: Pixabay CC0)
(Image: Pixabay CC0)

A solar eclipse will sweep across parts of Canada on April 8 - but watching it unprotected can damage your eyes. A total solar eclipse is a rare and special event. While the eclipse won’t be quite total in Waterloo Region, the deep partial eclipse will still be fascinating - and potentially damaging. Dr. Ralph Chou, professor emeritus in Optometry & Vision Science, is one of the world’s foremost experts on eclipse eye safety.

Why is the April 8 solar eclipse special for North America?

A solar eclipse is when the moon passes right between the sun and the Earth. In some eclipses, the moon isn’t quite big enough to cover the sun - that’s an annular (ring) eclipse. Other times, the moon doesn’t completely cover the sun - that’s a partial eclipse. However, the eclipse on April 8 is a total eclipse - for most of us, a once-in-a-lifetime experience.

For people within the path of totality, which in Canada ranges from Pelee Island to Newfoundland, the sun will be fully covered for a few to several minutes, and the faint outer atmosphere of the sun will be visible.

What are the dangers of looking directly at a solar eclipse?

We reflexively avoid looking at very bright objects. However, during an eclipse, our curiosity may encourage us to look at the sun even if it’s uncomfortable. The high level of light that reaches the back of the eye can damage the light-sensitive cells. Depending on the amount of damage, the visual symptoms may be transitory; they may last a long time - perhaps months - or they may be permanent.

The part of the eye most damaged by looking at the sun without protection is the fovea, which we use to see fine details. While you may not lose all’your vision, you may have difficulty with tasks such as reading. You could even end up legally blind.

How can the public safely view the eclipse?

There are inexpensive devices available that enable you to view the eclipse safely. These include solar viewers, which you hold up to your face, and solar eclipse glasses, which you can wear like spectacles. These are fitted with special filters, so they’re safe to use if they cover your eyes completely. If you wear glasses, they go over the top.

Make sure your solar viewer complies with the international standard, ISO 12312-2. The device should come with warning messages, instructions on safe use and a statement saying it complies with the standard.

If you’re in the path of totality, it will be safe to remove your solar viewer when the sun is fully covered. In Niagara Falls, for example, totality will last about three and a half minutes. The moment the tiniest sliver of sun returns, you must use your solar viewer again.

If you don’t have a solar viewer, you can make a pinhole camera, which projects an inverted image onto the inside of a box.

What do people outside the path of totality have to consider?

For people in Waterloo Region and anywhere even slightly outside the path of totality, there will never be a point when it’s safe to look at the sun without a certified solar viewer. While it may get darker during a deep partial eclipse, the sun will never be fully covered, so even the tiny crescent that’s visible can damage your eyes.

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