This year, when you look up at the sky on Christmas morning, you'll get a Christmas treat that no one has had in decades — a full moon.

The last full moon of 2015 will rise at 6:11 a.m. ET on Christmas Day.

If you're younger than 38, this will be your first Christmas full moon. The last time a full moon fell on Christmas was in 1977.

The next Christmas full moon is isn't expected until 3:54 a.m. ET in 2034, according to the U.S. Navy Astronomical Applications Department's moon phases predictor.

However, there will be a full moon on Boxing Day in 2017, which means the moon will look pretty close to full on Christmas Day that year.

Full moons fall on Christmas as often as they do on any other day of the year, but it's relatively rare for full moons to on any one day, whether it's Christmas or July 1 or your own birthday.

The moon becomes full every 29.5 days, or 12 to 13 times a year. But because the moon's cycle doesn't divide evenly into the number of days in our calendar year, the full moon(s) for a given month is shifted about 11 or 12 days per year. Next year's December full moon takes place on Dec. 14.