THE GREAT WINTER SOLSTICE OF 2020: Jupiter, Saturn and The Moon

Eric FitzgeraldBy Eric Fitzgerald      November 27, 2020

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THE GREAT WINTER SOLSTICE OF 2020:  Jupiter, Saturn and The Moon
Jupiter and Saturn with some of the brighter moons of both planets. The moons of Jupiter move fairly fast, so they might not be exactly in these positions when you train your telescope on the conjunction on the evening of December 21st. Ganymede is in transit here – or moving in front of the disk of Jupiter. Chart by Eric Fitzgerald
The winter solstice on December 21st this year comes with an added attraction – a great conjunction of Jupiter and Saturn. “What is a conjunction?” Merriam-Webster tells us that a conjunction is “the apparent meeting or passing of two or more celestial bodies in the same degree of the zodiac.” Readers of “The Backyard Astronomer” might recall from last year’s article, “The Winter Solstice: Secrets of the Ecliptic,” in the Messenger Mountain News, that the Sun, Moon and planets all travel across a path in the sky called the ecliptic, or the zodiac. When two or more planets “lap” one another along the ecliptic, the closest point they reach is termed a conjunction. Because Jupiter and Saturn are the most distant of all the bright planets, their orbits around the sun take the longest, so conjunctions of these gas giants are rare. Conjunctions between Jupiter and Saturn occur about every 20 years, but not all of these events are equally close. This time the two will be very close: a mere 0.1 degree of arc, or about 1/5 the diameter of the full Moon. This means they will be in the same field of a small telescope (see diagram). The last time these two planets were this close was 397 years ago. Imagine the wonder Galileo might have experienced, having just made his first telescope in 1609, witnessing a great conjunction of these two huge celestial bodies in 1623. Since Jupiter takes 12 years to make his annual trip around the Sun and Saturn takes 29 years to make the same circuit, their apparent motion against the background of stars is slow. You can see them approaching one another now. Find a location with a good view of the setting sun. In the canyon this might involve going up to Saddle Peak or any ridgeline that has an unobstructed view of the western horizon. Jupiter will be the brightest “star” that first appears in the evening twilight. Saturn will be the next brightest and the two will get closer and closer every evening right up until the conjunction that will occur by complete coincidence on the December 21st winter solstice. Astronomers, like ham radio operators, use Coordinated Universal Time (UTC) and avoid the confusion of all the local time zones. UTC is the time at the prime meridian on Earth, or 0 degrees longitude, that runs through The Royal Observatory in Greenwich, England. The exact moment that the sun reaches his lowest point in the sky, or the winter solstice this year, is 10:02 UTC or 2:02 a.m. PST here in Topanga. The exact point that Jupiter and Saturn are closest is at 13:22 UTC or 5:22 a.m. local time. As a bonus attraction, the very thin waxing crescent Moon will pass the planetary pair on the nights of December 16 and 17. The Moon will be closer on the evening of the 16 so get your cameras ready for this cosmic pile-up. Conjunctions were once thought to be omens of apocalyptic changes. Given the chaos of the global COVID-19 pandemic and the presidential election in the United States that have preceded this great conjunction of 2020, maybe these events were harbingers of the conjunction in a kind of upside-down oracle in this topsy-turvy year.
Eric Fitzgerald

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November 27, 2020

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