It makes ultraviolet light, that can cause sunburn and other skin damage
to people who are not wearing sun protection. Many people learn this the
hard way, but it might save a little grief and improve people's chances
with skin cancer if children were warned.
It is too bright to look at. Looking at the sun focusses its light on one
part of the retina, and tries to heat it to the temperature of the surface
of the sun. Eclipses of the sun and other events that bring the sun to
our attention tempt people to look directly at it. This is dangerous.
We should warn people not to look at the sun.
Lenses and the sun make a dangerous combination. The lenses we provide
can easily burn a hole in a piece of paper, or start a small fire.
The image of the sun on a white card is a very bright spot, so that just
looking at it will give "spots before the eyes" for many minutes afterwards.
For these reasons we recommend that you avoid doing optics investigations
with lenses or mirrors in any place where direct sunlight is available.
Wait for a cloudy day, or until the sun is not streaming into your classroom
windows!
Don't look at the sun!