Solstice, man

Winter Solstice at Stonehenge. Wow, that's funny cuz it's "STONE" henge.

 Some of the hairy, dred-headed, white kids who work at the bakery or are working on their degree in advanced harmonics may wish you a "Happy Solstice" today. It's not "Merry Christmas" but close. Take this very long article from ask.com for example:
The time around December 21 or 22 is a very important day for our planet and its relationship with the sun. December 21 is one of two solstices, days when the rays of the sun directly strike one of the two tropical latitude lines. In 2011 at precisely 12:30 a.m. EST (05:30 UTC) on December 22, 2011 winter begins in the Northern Hemisphere and summer begins in the Southern Hemisphere.
The earth spins around its axis, an imaginary line going right through the planet between the north and south poles. The axis is tilted somewhat off the plane of the earth's revolution around the sun. The tilt of the axis is 23.5 degrees; thanks to this tilt, we enjoy the four seasons. For several months of the year, one half of the earth receives more direct rays of the sun than the other half.
The earth's axis always points to the same point in the universe. When the axis points away from the sun from December to March (because of the relative location of the earth to the sun), the southern hemisphere enjoys the direct rays of the sun during their summer months. Alternatively, when the axis tilts towards the sun, as it does between June and September, it is summer in the northern hemisphere but winter in the southern hemisphere.
December 21 is called the winter solstice in the Northern Hemisphere and simultaneously the summer solstice in the Southern Hemisphere. On June 21 the solstices are reversed and summer begins in the northern hemisphere.
http://geography.about.com/cs/calendarsseason/a/winter.htm

Most liturgical texts will tell you that the two solstices are the basis of the dates set for Christmas and the Birth of St. John the Baptist.
For Christmas, this may be coincidental with the "birth of the unconquerable sun" (natalis invicti), a feast commemorating the birth of Apollo the Sun God who will overcome the darkness with his birth. The shortest day of the year, the darkest day, will be overtaken by the sun. The connection to the "Son" of God is obvious. Pope Benedict has written that the date of Christmas, December 25th, is due to the Annunciation being set at March 25th thus not falling on the date of solstice.

Sol Invictus/Apollo rising

For St. John the Baptist's birth (June 21), the feast falls on the Summer Solstice or the longest "day" of the year, harkening to John's saying: "He must increase while I must decrease" (John 3:30) speaking of Jesus' proclamation of the Kingdom and the end of the darkness.