How can a solar eclipse hurt your eyes?
During a total solar eclipse, most of the visible light coming
from the sun is blocked (from the point of view of those who can
actually witness the eclipse). As a result, it is physically
possible to look at the moon as it is blocking the sun. The problem
is that your pupils will be relatively wide open, and non-visible
radiation that is extremely harmful to the eyes will be able to
pour into your eyes, and you will not feel it or sense it
initially. The extreme pain/discomfort that you feel when your line
of sight nears the visible sun is a very important reaction meant
to keep you from being so foolish as to force yourself to look.
Don't look directly at the sun, and don't look directly at a
solar eclipse. You could cause blindness or serious loss of vision
by doing such things. There are materials that can be safely used,
with supervision, to make these observations, and be sure that
materials are safe before you use them.