Watching an eclipse safely

During a solar eclipse you might think the dimmed Sun is safe to look at. It is not. Even during an eclipse, sunlight is strong enough to damage your eyes and cause blindness.

So never look at a solar eclipse directly. And not through sunglasses, binoculars or telescopes either — sunglasses are far too weak, and binoculars and telescopes make the light even more concentrated and dangerous.

Planetaria and astronomy clubs hold eclipse-viewing events. Going to one is the best way to watch: they give you special eye protection made for looking at the Sun, and explain the science.

There is a safe indirect way too: use a mirror to throw an image of the Sun onto a wall, and watch the wall, not the Sun. Holding a mirror at the right angle for the whole eclipse is hard, so the book suggests a stand: a hollow ball with a small hole, half filled with sand so it stays steady, with a small embroidery mirror stuck on, resting on a ring (like an adhesive-tape roll) so it can be turned easily. Do this only with a teacher, and never point the reflected beam into anyone's eyes.

People have watched and recorded eclipses since ancient times. When nobody knew the reason, they were afraid: something blocking the Sun, our source of heat and light, even for a short time, would have been frightening. Many superstitions grew up about things not to do during an eclipse, such as eating, cooking or going outside.

Now we know exactly why eclipses happen, so there is nothing to fear — as long as we do not look at the Sun directly. In fact, scientists travel across the world to see eclipses, because they let us study things that cannot be seen at any other time.

An eclipse is called grahan in Sanskrit and many Indian languages. Many ancient Indian astronomy texts give calculations to predict eclipses; the best known is the Surya Siddhanta.