Winter Solstice Eclipse tonight

The full moon will pass through Earth's shadow, changing from gray to a rusty, red color.

Why red? NASA describes it this way:

A quick trip to the Moon provides the answer: Imagine yourself standing on a dusty lunar plain looking up at the sky. Overhead hangs Earth, nightside down, completely hiding the sun behind it. The eclipse is underway. You might expect Earth seen in this way to be utterly dark, but it's not. The rim of the planet is on fire! As you scan your eye around Earth's circumference, you're seeing every sunrise and every sunset in the world, all of them, all at once. This incredible light beams into the heart of Earth's shadow, filling it with a coppery glow and transforming the Moon into a great red orb.

If you're not much for staring at the sky, at least glance up once: early Tuesday morning at 12:17 a.m. That's when the eclipse will be most striking, according to astronomers.