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Star Points: Upcoming conjunction of Jupiter and Saturn to be a memorable sight

Way back in 1997 this column carried a summary of explanations for the legendary “Star of Bethlehem.” It won’t be repeated this month. However, one conclusion does seem to be of some importance and may be used for dismissing the most unlikely origins, including comets, meteors or even supernovae.

The most important revelation for me was that the “star” could not have been a kind of Christmas card-like bright shining beacon beaming shafts of light down to the ground. That would have been too easy. How do we know that this picturesque scene was not the case?

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An explanation supporting this conclusion is in the biblical book of Matthew. Upon entering the land of Judea, the Maggi or “Wise Men” payed a courtesy visit to King Herod. It seems this was the customary thing to do when traveling VIPs entered a foreign realm. The Wise Men explained that they were looking for the new king, recently born in Judea. Furthermore, the event was broadcast via some kind of celestial phenomena involving a “star” they had viewed from their homeland in the east.

How was it possible for foreigners to carry news of a hitherto unknown Hebrew king in the land that Herod himself ruled? Were they spies working to undermine his rule?

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It was said that Herod was troubled by the news, and perplexed as well as enraged, I would imagine. Why was he the last to learn about a new rival king – and right under his nose? He called his best priests and scribes and demanded to know where the star was and why nobody had noticed or mentioned it before. Word must have spread because it was said that the entire city of Jerusalem was troubled as well.

Obviously, not a single soul in the entire capitol could understand or interpret the wisdom of the Maggi. So much for a bright star beaming in the sky like one of those grotesquely obtrusive modern “crazy bright” night lights popping up on garages in Carroll County.

The most convincing explanation I have heard for the star continues to be a conjunction of planets. As important as the conjunction itself was, there was also the factor of, as realtors would call, “location, location, location.” That is, where in the sky, or constellation, such a conjunction had occurred.

Known constellations varied according to culture and, for the Maggi at least, the hypothetical planetary conjunction occurred in a constellation associated with the House of Judah. The constellations differed in Judea although the same stars appeared in the skies of both lands.

There was an ongoing planetary conjunction during the Christmas season when I was 13. I read how a “triple conjunction” similar to the one happening at that time might have been the star of Bethlehem. I set the alarm clock and woke up in the pre-dawn of Christmas morning to check the Santa gifts and go outside and look at the planetary “star.”

The planets conjugating then are the sky’s brightest: Venus and Jupiter. Mars was also hovering nearby, as well as the crescent moon. It was an impressive grouping low in the sky for someone like me who was unaccustomed at the time to naked eye planet viewing. It was a dazzling sight.

Unfortunately, I misunderstood the meaning of “triple conjunction.” I thought it referred to those three planets meeting together. A triple conjunction actually meant a conjunction of two planets that occurs and then repeats twice more.

For a conjunction to repeat, one of the planets must appear to reverse course and back up in order for them to meet again. This happens thanks to “retrograde motion.” Retrograde motion is the result of the relative orbital motions of the planet and the Earth creating the illusion that the planet is moving backward against the background stars. Same thing happens when one car passes another on the highway and the slower car appears to be moving backward in relation to the passing car although both are in fact traveling in the same direction.

Retrograde motion is not instantaneous. Before retrograding, a planet’s daily motion in the sky will appear to slow, stop, reverse course, and accelerate. Matthew possibly acknowledges the onset of this retrograde motion. “[T]here, ahead of them, went the star that they had seen at its rising, until it stopped over the place where the child was.”

According to the theory and the astronomy, this triple conjunction of Venus and Jupiter took place in the time span of 2-3 B.C. But there is another Star of Bethlehem theory involving yet another triple conjunction.

In December 1603 astronomer Johannes Kepler observed a conjunction of Jupiter and Saturn. He later calculated that a triple conjunction of these planets occurred in 7 B.C. In modern times it was hypothesized that this could have been the “star” observed by the Maggi.

Was it? No one knows for sure. Besides not knowing the actual year of Jesus’ birth, there is no guarantee that the Maggi’s journey occurred at the same time as the birth. Perhaps they traveled some time after making their observations. When Herod’s cancel culture commanded the infanticide of male children in order to nullify the presumptive new king, he specified that the order include boys up to the age of 2.

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During the 7 B.C. triple conjunction, Jupiter and Saturn were never much less than 1 degree apart. But this month, we are witnessing an even more dramatic conjunction than then!

Jupiter orbits the sun about every 12 years and Saturn about every 30. Once every generation or so Jupiter catches up to Saturn for a “Great Conjunction.” The year 2020 is a great conjunction year and one in which the planets’ angular separation is exceptionally close.

On Dec. 21, the same day as the Winter Solstice, Jupiter and Saturn will appear only 0.1 degree apart, or the closest apparent separation since July 1623! However, back then the planet pair would have been very low in the west during bright twilight and was likely unobserved.

This year is different, however. During December the planets will move closer together low in the southwestern sky. They are the brightest objects in that region of sky. You should look between 5:30 and 6 p.m., before they get too low and set for the night. Keep an eye on them as the month progresses and see how the gap between them is shrinking.

By Dec. 20, and for the next couple of nights, Jupiter and Saturn will appear to be extremely close together. Hopefully, one of those nights will be clear. With a low horizon and good eyesight one should be able to separate them. In a telescope they will fit easily in the same field of view in a low-to-medium power eyepiece along with their brighter moons.

No telescope? Then try using binoculars. No matter how you observe it, the 2020 great conjunction of Jupiter and Saturn will be a memorable sight, and a great way to cap the year 2020.

Curtis Roelle is a member of the Astronomical Society. His column appears the first Sunday of each month. His website is www.starpoints.org, and he can be reached at starpoints@gmail.com.

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