...the Calendar, and how we got it, the Pope's talk today (winter solstice), is of interest. Among other things, he noted that "The occurrence of the feast of the Nativity itself is linked to the winter solstice, when in the northern hemisphere, the days start to lengthen.
In this respect, perhaps not everyone knows that there is a great meridian on St. Peter's Square. In fact, the Obelisk casts its shadow along a line that follows the pavement towards the fountain beneath this window, and these days, is the longest that it casts during the year.
This reminds us of the function of astronomy in marking the times of prayer. For instance, the Angelus is recited in the morning, at midday and in the evening, and clocks and watches are timed to the meridian which in the past served precisely to determine the 'true midday'."