This book offers a lighted-hearted scientific look at the rituals and icons of Christmas. 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 edition has been extensively updated and contains a new chapter on the latest seasonal science - how religion can help your mental life!