Hello, friends! Welcome to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of scientific terms. Today on Sciency Words, we’re talking about the word:
We’ve all seen pictures like this, with all eight planets lined up in a row:
And sometimes, on extra special occasions, the planets really do line up like that, or at least they come very close to it. When this happens, we call it a grand syzygy.
The word syzygy traces back to ancient Greek. It originally meant “yoked together,” as in: “The farmer yoked together his oxen before plowing the field.” According to my trusty dictionary of classical Greek, the word could also mean “pair” or “union.”
Some closely related words in Greek referred to balance, teamwork, sexy times, etc. And our modern English words synergy and synchronized have similar etymologies. Basically, what all these words have in common is a sense of people or things coming together, in one manner or another.
For modern astronomers, syzygy means three or more celestial bodies coming together to form a straight line. The most commonly cited example of this is the alignment of the Sun, Earth, and Moon that occurs during either a new moon or full moon, as observed here on Earth.
But an alignment doesn’t have to be perfectly straight to be called a syzygy, especially when we’re dealing with more than three objects. According to this article from The New York Times, a syzygy of the Sun, Venus, Earth, Mars, Jupiter, and Saturn occured between March 25 and April 7, 1981. The Sun and five planets came “within 2 degree of arc from a perfect straight line.” Apparently that’s close enough.
But while that 1981 syzygy was pretty grand, it was not the grandest of grand syzygies. The planets Mercury, Uranus, and Neptune were left out. According to another article from The News York Times, a truly grand syzygy will happen on May 19, 2161, “[…] when eight planets (excluding Pluto) will be found within 69 degrees of each other […].”
So mark your calendars, friends! You don’t want to miss the grand syzygy of 2161!
P.S.: And if you’re a Star Trek fan, you may recall that 2161 will be an auspicious year for another reason. That’s the year when the United Federation of Planets will be founded—a political syzygy, one might say, occurring at the same time as an astronomical syzygy.