Jupiter and Saturn are about to treat stargazers with The Great Conjunction, a rare astronomical event.
THE GREAT CONJUNCTION
We’ve watched Jupiter and Saturn make their way across our night sky all summer and fall, but before they vanish from sight until next year, something extraordinary is going to happen. From our view on Earth, they will get so close it will look like they touch. In the vocabulary of astronomers, this is called a conjunction.
When will this take place? On the Winter Solstice, which is Monday, December 21, 2020.
Jupiter and Saturn form a Great Conjunction about every 19.6 years, but some years they are much closer than others. In fact, this year they will be about 0.1° apart from one another, making it possible to see them both in a telescope at the same time. The last time they appeared this close to one another was in 1623. That was only fourteen years after Galileo pointed his first telescope at these two stunning celestial objects. The next time they will be this close will be in the year 2080.
Ted Blank, my guest on the first episode of the Night Sky Tourist podcast, will do a live virtual presentation of the conjunction where you will be able to see what his telescope sees. He is doing this in partnership with Arizona State University’s Marston Theater. The link has not yet been released as of the time of this writing, so CLICK HERE about a week before to register. Registration is free, but is required to receive the event link.
Human history is filled with superstitions about cosmic events. The belief that comets, solar and lunar eclipses, and conjunctions were omens and predicted both good and bad things for humans on Earth held fast for thousands of years. Some people still find those ideas to be tantalizing, keeping the practice of astrology alive to this day.
Jupiter is the fifth planet from the Sun and the largest planet of all. It would take one thousand Jupiters to equal the size of the Sun, but it would take 1,300 Earths to equal the size of Jupiter. Jupiter is famous for its colorful stripes and its Great Red Spot. These are powerful storm clouds. The Great Red Spot is so large, three Earths could fit inside of it.
Astronomers have discovered 79 moons around this gigantic planet. Galileo was able to find four of them when he first pointed a telescope that way. You can spot those same four moons if you look through a telescope or binoculars from your backyard.
It takes Jupiter almost twelve Earth-years to make one trip around the Sun. But it spins on its axis faster than any other planet, making its day less than 10 hours long. Because it spins so fast, it bulges at the center, something you can notice when looking at it through a telescope.
Jupiter is not a solid planet like Earth. The planet is made of gas, so there is no solid surface.
Jupiter does have some rings, but they are not impressive like the ones around Saturn. Jupiter’s rings are made of dust instead of ice, so they are difficult for us to see from Earth. You will not be able to see them with any instrument from your backyard.
Jupiter is usually the fourth brightest object in the sky after the Sun, Moon, and Venus. However, Mars was close enough to Earth this Fall that it was brighter than Jupiter. That won’t happen again for another 15 years.
Ancient cultures around the world had different mythologies about the objects they saw in the night sky. Jupiter was often seen as a representation of their gods.
To the Babylonians, Jupiter represented their god Marduk.
To the Hindu astrologers, it was Brihaspati, the teacher of the gods. They often called it “Guru”.
In Germanic mythology, it was Thor, the god of thunder. We get the name Thursday from Thor… Thor’s Day.
The Chinese, Vietnamese, Koreans, and Japanese see it as the “Wood Star” based on the Chinese Five Elements.
For the Greeks, Jupiter was the same as their god Zeus.
But we get the name Jupiter from the Romans. Jupiter was the Roman god of the sky, also known as the Father Sky-God.
Saturn is the sixth planet from the Sun and the second largest after Jupiter. Nearly 760 Earths could fit inside of the ringed planet. It is twice the distance from Earth as Jupiter and it takes light one hour and 29 minutes to reflect back to us. In other words, as you look at Saturn in the night sky, that’s actually where it was almost an hour and a half ago, but it took that long for the light to reach your eyes.
It takes Saturn 29 Earth years to complete one orbit around the sun, but its day is only a little more than ten and a half hours long. This makes Saturn noticeably bulge at the center.
Saturn is less dense than water, so if you had a swimming pool large enough to hold it, it would float. The reason is that the planet is made almost entirely of gas, so it has no solid surface, just like it’s neighbor Jupiter. Astronomers believe that two tons of Saturn’s mass came from the Earth, which creates some very interesting questions.
Galileo was the first person to look at the planet with a telescope. He thought it had handles or arms sticking out from it. But 45 years later, after telescopes got a little better, another astronomer, Christiaan Huygens, announced that Saturn actually had a disk or rings orbiting it.
The beautiful rings are part of what makes us love it so much. They are mostly made of ice and rock. Some are as small as a grain of sugar and some are as big as a house. A 2016 study showed that the debris that makes up the rings could be the remains of dwarf planets that broke apart in an extremely distant past.
Saturn has 82 known moons. Titan is the largest, and it is even bigger than Mercury. It is the second largest moon in the entire solar system. Jupiter’s Ganymede is the largest while our Moon is the fifth largest. Some of Saturn’s moons may be able to support life because they contain water. One of them even has about a hundred spouting geysers!
Saturn is named after the Roman god of wealth and agriculture. In ancient Greek culture, Saturn represented the god Kronos, the god of time.
In Hindu astrology, Saturn is called “Shani” and he judges everyone based on the good and bad deeds they did during their life.
In the ancient Chinese and Japanese cultures, it is known as “Earth Star”, which is based on the Chinese Five Elements.
Our favorite day of the week was named in honor of Saturn…Saturday.
But it was the Romans who had the most extensive myths about the planet. They believed the god Saturn was the father of Jupiter, Neptune, Pluto, and others. Every year in December, the Roman’s celebrated the festival of Saturnalia at the time of the Winter Solstice. It was a time of feasting, role reversals, free speech, gift giving, and revelry. Some of these traditions found their way into the Christmas holiday.
It seems relevant that Saturn would put on such a great show, along with Jupiter, on the Winter Solstice. What a great way to commemorate the ancient festival of Saturnalia this year.