What does this strange-sounding word mean in the world of astronomy?

Syzygy. That’s what this week’s ‘An eye for an i’ is all about. From Rutherford’s planetary model for an atom, we are moving on to a model or celestial configuration in which those planets and astronomical bodies are really involved.

About the word

Before we delve into the science of syzygy, let’s first look at some trivia. Derived from the greek word suzugos, which means yoked together, the word has a special place in the English language. Syzygy is among the shortest words which has three ‘y’s and is among the longest words with no vowels except y (which can be regarded both as a vowel and a consonant). Knowing this word might even fetch you 21 points in your next scrabble game, even without any letter or word bonuses. Of course, with only two Y tiles available in the scrabble set, you’ll have to use a blank tile in one of the spaces in the place of Y.

What is it?

In terms of astronomy, syzygy describes the scenario in which three or more celestial bodies align themselves roughly in a straight line. Though used commonly in reference to the configuration of sun, earth and either a planet or moon, it is not a phenomenon limited only to earth. In fact, even on occasions when celestial bodies involved are not in a line, but are scattered around in an unusual formation, it is referred to as a syzygy.

With respect to earth-sun-moon, there are two main forms of syzygy. When the sun and moon are in opposition, they appear on either side of earth. On the other hand, if the sun and moon are in conjunction, they seem to be very close to each other in the sky. Yes, you guessed it right. Solar and lunar eclipses are special cases of a syzygy.

While the gravitational effects of a syzygy on any planet still remains under consideration, its effects on ocean tides have been studied extensively. Syzygy produces spring tides, with the combined gravitational pull of the sun and moon working together on earth’s surface. Spring tides (highest tides) occur during new moon and full moon times while neap tides (lowest tides) occur when the sun and moon are at right angles.

Grand syzygy

On March 10, 1982, all nine planets (oh yes! Pluto was still a planet then) in the solar system and earth’s moon were on the same side of the sun at the same time. This grand syzygy saw all the planets spread out over 98 degrees, with the four major planets, Jupiter, Saturn, Uranus and Neptune, spanning an arc of about 73 degrees.

While the run up to the day was preceded with numerous doomsday predictions, none of it came true. Astronomers do believe that these are safe, while agreeing that a lot more needs to be explored in relation to such configurations. We wouldn’t be around for the next such grand syzygy though, which is expected to take place on May 19, 2161. Eight planets (excluding Pluto, which isn’t a planet now anyway) will be found within 69 degrees of each other and we should hopefully have more than just doomsday predictions to go by then.

ganesh.a.s@thehindu.co.in

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