Happy DongZhi, or in chinese, 冬至快乐! It’s amazing now that you think about it, the ancient chinese calculated this annual path of the sun which coincides with the winter solstice. The winter solstice is when the sun has gone as far south (if you live in the northern atmosphere of the earth) as it can through the winter, and is now on its way back to warm your icy cold butts. The chinese calendar is actually a combination of the lunar and the solar path, which is far more useful in predicting the occurrence of the full moon, the seasons and maybe even the eclipses (not sure).
Anyways enough of the technical details. Go ahead and enjoy your “tang yuan” 汤圆 with your family! 😉