This week begins with December solstice, the official start of the astronomical season of winter in the northern hemisphere. And, the huge deal right now for star gazers is the once in a lifetime great conjunction. Also called the Christmas Star. Even though it's not a star and happens four days before Christmas. Two planets, the biggest and most distant in our solar system visible from earth, Jupiter and Saturn, will form the closest visible alignment in hundreds of years. Our Kim Yeon-seung is at Gwacheon National Science Museum. Yeon-seung, so why are you out there and what happens when these two planets collide?