How to Observe the Sun Safely pp 17-39
Equipment for Observing the Sun
Let us begin this chapter by repeating the warning given at the start of the book. NEVER LOOK DIRECTLY AT THE SUN THROUGH ANY FORM OF OPTICAL EQUIPMENT, EVEN FOR AN INSTANT. A brief glimpse of the Sun through a telescope is enough to cause permanent eye damage, or even blindness. Even looking at the Sun with the naked eye for more than a second or two is not safe. Do not assume that it is safe to look at the Sun through a filter, no matter how dark the filter appears to be, because the danger of observing the Sun is caused less by its exceedingly bright light – though that would be enough to blind you if you looked at it for long enough – but by its invisible radiation.