PHILADELPHIA: Gaze up into the sky and you'll see something rare. And, no, it won't be Santa. He and his reindeers will have already zoomed across the horizon.

On Christmas Day, there will be a full moon, the first since 1977. It will reach its peak at 6:11 a.m. EST.

This full moon, the last one for 2015, is called a Full Cold Moon because it happens during the start of winter. Though "cold" is relative these days. On the balmy US East Coast, some people will be tempted to celebrate the holiday in shorts and flip flops, more like Hawaiians.