Guillermo Gonzalez is an astronomer in the Department of Physics and Astronomy at Ball State University in Muncie, Indiana. He received his Ph.D. in astronomy from the University of Washington, Seattle in 1993.
This year a close conjunction between Jupiter and Saturn marks the start of the winter solstice, only four days before Christmas. Although Jupiter and Saturn have a conjunction every 20 years, this one is the closest observable one since 1226. At their closest, visible to observers in Europe, the planets will appear about 1/5 of the moon’s diameter apart. For observers in the continental U.S., they will appear slightly farther apart.
This conjunction makes for two interesting visual effects. First, on the evening of December 21 observers with below average visual acuity will see the pair of planets as one bright star low in the southwest. If you have good eyesight, you should be able to see them as separate points of light. If you follow them for several evenings before and after the conjunction you can watch as they approach each other, “merge,” and then separate. It is during rare close conjunctions like these that the motions of the planets in the sky are most evident. ….