Some of these catalogs were compiled by astronomers while they were searching
for other objects. For example, Charles Messier, who compiled his catalog in the
eighteenth century, was studying the sky with his small telescope, searching for
comets. Distant comets and what he called “cloudy objects”
looked similar through his telescope. So, he began to compile
a list of the objects that he knew were not comets, in order to
make his comet-hunting easier.