This perennial Christmas bestseller takes a lighted-hearted scientific look at the rituals and icons of Christmas. What are the thermodynamics involved in cooking a turkey? What are the likely celestial candidates for the Star of Bethlehem? Is the concept of a virgin birth scientifically feasible? What happens to us physically when we overindulge in alcohol? How does snow form? Why are we always depressed after Christmas? How does Santa manage to deliver all those presents in one night? (He has, in fact, little over two ten-thousandths of a second to get between each of the 842 million households he must visit.) This new paperback edition has been extensively updated and contains a new chapter on the latest seasonal science - how religion can help your mental life!