Christmas Day in 2012 falls on a “Tuesday”, the English-language word for the second (or third) day of the week named for the Norse-pagan deity Tyr (also called Tiews, Tiw, Ziu and Cyo).
We all call this day of the week “Tuesday” without believing in Tyr—including Christians—so it follows that we can all celebrate Christmas as a joyful winter holiday on December 25 without believing in its namesake, Jesus Christ. Except for some of the music and the nativity scenes, there is nothing about Christmas that is inherently Christian.
It is well-understood that the Roman Catholic Church placed the holiday at the winter solstice as a likely attempt to co-opt the existing pagan holiday of Dies Natalis Solis Invicti (birth of the unconquered sun god) to easier convert pagans of the time. Whether the Church intended it or not, this supplantation resulted in the paganization of one of their most holy feasts (Easter, itself even more pagan, is a whole other story).