For more about Kant's Nebular Hypothesis, visit physicist Dr. Russell McNeil's essay on Kant.
These publications offer brief, easy-to-understand summaries of Kantian ethics:
Grassian, V. Moral Reasoning: Ethical Theory and Some Contemporary Moral Problems (Saddle River, NJ.: Prentice Hall, 1992; Chapter 10)
Kuehn, M. Kant: A Biography (Cambridge, MA: Cambridge University Press, 1986)
Pojman, L. Ethics: Discovering Right and Wrong. (Beverly, MA: Wadsworth Publishing Company, 1999; Chapter 7)
Sommers, C. Right and Wrong: Basic Readings in Ethics (New York: Harcourt Brace Jovanovich Publishers, 1986; Chapter 1)