The last time a lunar eclipse happened on the winter solstice was in 1554. And according to EarthSky, there won’t be another total lunar eclipse this far north on the sky’s dome until December 21, 2485.
If you want to know if and when you can see the eclipse, check out this site - it talks all about it and lists the best times to see it. In my area, Mountain Time, it will be totally eclipsed at 12:41 am on December 21. Total eclipse ends at 1:53 am. So it's a good full hour of lunar eclipse viewing.
What is a lunar eclipse?
When the sun, earth and moon all align and the moon passes through earth's shadow you get a lunar eclipse. The only time this can happen is during a full moon. I'm a visual person, so here is a diagram showing how this works.
So essentially, the moon is at just the right angle to pass into earth's shadow. During most full moons, the moon is still directly across from the sun, however it is not lined up with the earth allowing the earth's shadow to pass over it.
Now, unlike what you might expect when this happens, the moon does not go totally black, or even kind of gray. It turns a beautiful, deep orange/red. Why is that? Here is a little explanation from NASA about why this happens: