Before 2020 comes to a close, Jupiter and Saturn will be so close that they will appear to form a "double planet." The great conjunction, as the planetary alignment has come to be known, hasn't occurred in nearly 800 years. When their orbits align every 20 years, Jupiter and Saturn get extremely close to one another. This occurs because Jupiter orbits the sun every 12 years, while Saturn's orbit takes 30 years — every couple of decades, Jupiter laps Saturn, according to NASA. However, 2020's conjunction is especially rare — the planets haven't been observed this close together since medieval times, in 1226.