Explain the reasons for eclipses (lunar and solar)

The reason for eclipses is that something moves into a position
where a shadow is noticeable.

When the moon moves into the Earth's shadow, it turns dark ... since the sun is
what lights it up anyway.  Everybody on the night side of the Earth who happens
to notice sees the moon turn dark, and they say "hhh !  A lunar eclipse !"
and then most of them go about their business.

When the moon moves to a place where its shadow falls on the Earth's surface,
the effect is that people who are in or near the end of the shadow see all or part
of the sun go away for some short period of time.  Those that are in the right
place and happen to notice say " !  A solar eclipse !" and then most
of them go about their business.