Intuitive

Credit: N.R.Fuller, National Science Foundation

Concrete

• The expanding universe by Markus Pössel; "An introduction to the physics and mathematics of the expanding universe, using no more than high-school level / undergraduate mathematics. "

Recommended Textbooks:

• The best introductions are Relativity, Gravitation and Cosmology by Ta-Pei Cheng and
• The Early Universe by Edward Kolb and Michael S. Turner
• Edward R. Harrison, Cosmology, the Science of the Universe
• M. Berry, Cosmology and Gravitation

• Another nice introduction to the CMB and related effects is A Poor Man’s CMB Primer and Student Friendly Guide to the Cosmic Microwave Background by Robert D. Klauber

Abstract

Recommended Books:

• John A. Peacock, Cosmological Physics

Why is it interesting?

FAQ

Many questions that frequently pop up in cosmology are answered here and here