The planets Jupiter and Saturn have been moving closer and closer to each other in the night sky.In fact, on December 21, they appear closer together than they have in hundreds of years.When two astronomical bodies appear close in the sky, as seen from Earth, it is called a conjunction.Conjunctions can happen with any two bodies, such as planets, moons, stars and asteroids.When Jupiter and Saturn come together, it is called a "Great Conjunction."Astronomers say these events between the two largest planets in our solar system are not especially rare.Jupiter passes its neighbor Saturn once every 20 years as they circle around the sun.But this conjunction is especially close: From Earth, the two planets will look to be just one-tenth of a degree apart.That is about the distance of one-fifth of a full moon.If weather permits, they should be easy to see just after sundown.This just-in-time-for-Christmas sight promises to be one of the greatest of Great Conjunctions.
