Jupiter and Saturn appear to pass each other in the sky about once every twenty years. When this happens, astronomers call it a great conjunction. In the early 1600s, Johannes Kepler was noticing one of these great conjunctions. Because of his knowledge of planetary motions, he was able to calculate the positions of the planets just before Christ’s birth. He noticed that there was a great conjunction in which Jupiter and Saturn passed close by each other not once, but thrice. The planets then had conjunctions with the Sun. He suggested these conjunctions may have heralded the birth of Christ.
While God did create the heavens to have rare conjunctions around the time of Christ’s birth, the star the wise men saw leading them from Jerusalem to the house where Jesus was, likely was a supernatural light. It could be followed, and it clearly marked a specific house.
On the first day of winter, December 21 of last year, another great conjunction happened. It happened only a few days from Christmas, so a lot of people were thinking of it as a replay of what had happened about 2,000 years ago. It was nicknamed the “Christmas Star.” Another reason this conjunction got so much attention was that the two planets were unusually close together, close enough to be seen together in a telescope. They appeared only one-fifth of a Moon width apart. But in reality, they were only aligned, and Saturn was about twice as far away from us as Jupiter.
The last time Jupiter and Saturn appeared this close was 397 years ago on July 16, 1623. That time, they were too close to the Sun’s glare to be seen by most people. The most recent clearly-visible conjunction that was closer than this one happened March 5, 1226. It was almost 800 years between that great conjunction and the most recent one. The next one of comparable closeness will happen on March 15, 2080.
The Moon appears much larger than Saturn, and it passes Jupiter about once a month, instead of once every twenty years like Saturn. Because of this, there’s more opportunity to see Jupiter next to the Moon. A couple of years from now on May 17, 2023, the Moon and Jupiter will rise together. The conjunction will then progress into an occultation. The Moon will appear to overrun Jupiter a little after 7 am EDT. Jupiter will reappear on the other side of the Moon about an hour later. As an added bonus, two of Jupiter’s moons will be casting their shadows on Jupiter in what’s called a double shadow transit. You’ll need a telescope to see this. Be careful if you try for it, because the Sun will only be about 25° away, and it would be dangerous to point your telescope toward the Sun.
If you prefer a safer and easier way, you could use the free planetarium software or app called Stellarium to see a simulation of it at any time you choose by setting the date to May 17, 2023.
