On Monday night, a bright light will appear in the nighttime sky, the result of a rare convergence of the largest planets in the solar system that was last seen almost 800 years ago. On the night of December 21 (the Sixth of Tevet on the Hebrew calendar), the solar system’s two largest planets, Saturn (שַׁבְתַאִי Shabtai in Hebrew) and Jupiter (צדק, Tzedek in Hebrew), will appear to unite, creating a particularly bright point of light in the southwestern heavens. The night also happens to be the winter solstice in the northern hemisphere when the North Pole has its maximum tilt away from the Sun and marks the shortest day and the longest night of the year. The convergence will be in appearance only with the planets appearing to be separated by just one-tenth of a degree from our perspective or about one-fifth the width of a full moon. The two planets will not actually be close together and will, in reality, be 450 million miles apart. The two planets align once every 19.6 years but this particular astronomical phenomenon in which they appear as one point in the night sky has not taken place since dawn on March 4, 1623, but even then, the convergence occurred close to dawn and is not believed to have been visible. The previous sighting of Jupiter and Saturn converging was in the year 1226 when Genghis Khan was conquering Asia. It is not expected to appear again until March 15, 2080.