Some concepts in the teaching of Cosmology that almost always create confusion

Abstract The teaching of the evolution of the Universe is one of the most complex subjects that can be addressed in the classroom. The involved concepts are frequently very far away of any intuition, and are difficult to expose and discuss. We point out in this communication some of these basic concepts related to the Big Bang, analyzing their scientific content and the most common mistakes made by students and their teachers with the intention of improving the teaching of this branch of Science. The danger of didactical analogies commonly used are pointed out for each case.