Optometrists are warning people who want to view tomorrow’s eclipse not to stare at the Sun. Exposing the eye to the Sun for as little as one minute can result in sight-threatening damage to the eye.
Speaking on RTÉ’s Morning Ireland, Lynda McGivney Nolan of the Association of Optometrists Ireland said those who wanted to look at the Sun during the eclipse should use special eclipse glasses.
Ms McGivney-Nolan said the safest way to view the eclipse was to make a small hole in a card, hold it up to the sun and project the image on the ground or a second piece of white card. People should not view the Sun directly through the hole. Below are some other methods you can use.
Using a mirror
Cover a small flat mirror with paper that has a small hole cut in it. The hole does not have to be circular but should be no wider than 5mm. A larger hole will produce a brighter but fuzzier image.
Prop up or clamp the mirror so that it reflects the sunlight onto a pale screen or wall, ideally through a window. A projection distance of five metres (16.4 feet) will produce an image of the Sun just over 5cm across.
The eclipse can be seen in the image as the Moon starts to take a bite out of the Sun, appearing upside down compared with its position in the sky. If clouds move across the face of the Sun, they can be seen as well.
The smaller the mirror and further away the wall, the sharper the image will be. Experiment with the distances and mirror size. Do not look into the mirror during the eclipse as this is just as dangerous as looking directly at the Sun.
A big advantage of this method is that it allows a number of people to watch the eclipse at the same time—ideal for schools.
Pinholes allow light through them and can create an image like a lens. Make a small hole in a piece of card using a compass or other sharp-pointed implement.
Standing with your back to the Sun, position another white card behind the one with the pinhole so that the Sun projects an image onto it.
An alternative method uses a cereal box or something similar. Make a pinhole in one edge, point it towards the Sun, and a tiny image will be seen projected onto the inside of the box.
A piece of white paper or card placed inside will make it easier to see. Never look through the pinhole at the Sun.
Projection from binoculars or a telescope
Cover one eyepiece of a pair of binoculars with a lens cap and face the big end of the binoculars towards the Sun. The uncovered lens will project an image of the Sun that can be cast onto a plain card held about a foot away. Use the focus wheel to sharpen the image.
Ideally, the binoculars should be fastened to a tripod or stand. A cardboard collar with holes cut to fit the large lenses will shade the card on which the image is projected. A small telescope can be used the same way.
Take an ordinary kitchen colander and stand with your back to the Sun holding it in one hand and a piece of paper in the other. The holes in the colander can be used to project multiple eclipse images onto the paper.