Today, Sunday, November 27th, 2016 is
The First Sunday of Advent in Christianity
This is very unique in that it is the earliest possible day for Advent in any given year in the Catholic Church and for Christianity in general. That's because it's on a Sunday and because of that the fourth Sunday of Advent is a Sunday and the following week is Christmas day. Normally if it was another day of the week, the Christmas Day would be just the following Sunday. Since the fourth Sunday of Advent and Christmas Day cannot be on the same day, it is therefore the longest possible time in between.
The latest day possible for the first Sunday of Advent is December 3rd. Incidentally that's when it is next year! So this year it is the earliest possible Advent and next year it's the latest possible advent.
The rest of the Sundays of Advent are as follows:
1st Sunday of Advent 2016: November 27, 2016
2nd Sunday of Advent 2016: December 4, 2016
3rd Sunday of Advent 2016: December 11, 2016
4th Sunday of Advent 2016: December 18, 2016
Christmas Day: December 25, 2016