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By KAZUYA AYANI

Guest Contributor In our solar system , eight planets and innumerable small objects orbit around the Sun . The eight planets orbit in almost the same plane , including the Sun . When viewed from one of those planets , the Earth , the planets rarely appear to overlap because they are not in exactly the same plane , but sometimes the planets appear to be quite close . Also , the angular distance between the close encounters varies for each encounter . Jupiter ’ s orbit is tilted slightly with respect to Saturn ’ s orbit . Their orbital planes intersect at a slight angle . Seen from Earth , Jupiter ’ s orbit and Saturn ’ s orbit intersect at two points in the sky . Jupiter and Saturn orbit around the Sun in the same direction , but Jupiter has an orbital period of about 12 years and Saturn has that of about 30 years , so Jupiter orbits the Sun in a shorter time than Saturn . As a result , Jupiter catches up with and overtakes Saturn about every 20 years . At this time , Jupiter and Saturn approach each other when viewed from the earth , but the interval at the time of the closest approach differs depending on how far the orbits are separated seen from the earth . In December of this year , Jupiter and Saturn approach each other where the separation between the two orbits is very small . In fact , on December 21st this year ( in this article , dates and times are expressed in Universal Time ), Jupiter and Saturn will approach each other by 6 arcmin ( one-fifth the apparent size of the full moon ). It will be the first time in 397 years since July 16th , 1623 , that they are this close . The next close encounter to the same level as this time is March 15th , 2080 , about 59 years later , so it is a phenomenon which can be seen once or never in a lifetime . Saturn ’ s orbital period is about 30 years , and the

COURTESY

Position of the planets in the Solar System on December 21st , 2020 . Not in scale .

cycle of Jupiter and Saturn ’ s close encounter is about 20 years , so similar close encounters occur every 60 years . The close encounters of 20-year cycle from 1900 to 2100 are shown in the following table . ( Calculated with Astroarts StellaNavigator 11 ).