Today the Sun Stands Still

Happy December solstice! There may be a few more months of this, though.

Photo by Phil Plait

Today is the real reason for the season: It’s the winter solstice! If you’re a purist, then raise your glass at 23:03 UTC (18:03 Eastern US time), because that's the moment the solstice occurs.

There are a lot of ways to look at this, but they all boil down to the Earth’s axis being tilted with respect to its orbit. You’ve seen this with classroom globes; they’re tipped by about 23.5°. As it orbits the Sun, the north pole of the Earth’s axis is always pointed pretty close to Polaris in the sky, which means that sometimes the axis is tipped toward the Sun, sometimes away. When it’s tipped as far from the Sun as it can be, that’s the moment of the winter solstice.
Read more http://www.slate.com/blogs/bad_astronomy/2014/12/21/winter_solstice_dec_21_2014.html