Space Stories - Syzygy, When Worlds Line Up

0:00It's the 365 Days of Astronomy podcast. Coming in 3, 2, 1.

0:20Welcome to the 365 Days of Astronomy. I'm Aviva, your host. There are some words in astronomy that sounds as if they were invented for science fiction. This one has six letters, three Ys, and almost looks impossible to pronounce. S-Y, Z-Y, G-Y. S-U-Z-Y. And here's another strange things about it. S-U-Z-Y has none of the conventional vowel letters. A-E-I-O or U. It may look alien, but S-U-Z-Y describes something that happens regularly in our own sky.

0:52A full moon? S-U-Z-Y. A new moon? Also a S-U-Z-Y. A solar or lunar eclipse? Definitely S-U-Z-Y. So what does this strange little word actually mean? This is astronomy verse where we explore the words astronomers use to describe the universe and the stories hidden inside them. The word S-U-Z-Y comes through Latin from the Greek S-U-Z-Y-G, meaning a union or pairing. Behind it are two older pieces, S-U-Z-Y, meaning together, and S-U-Z-Y-G, meaning Y-O.

1:24A Y-O connects things together. The same Greek root also appears in the word S-U-Z-Y-G, where two reproductive cells join together. And that is the basic idea behind S-U-Z-Y, things join together. In astronomy, a S-U-Z-Y is a roughly straight-line configuration of three or more celestial bodies in a gravitational system. The most familiar example involves the sun, earth, and moon. At new moon, the moon lies roughly between the earth and the sun.

1:55Sun, moon, earth. At full moon, earth lies roughly between the sun and the moon. Sun, earth, moon. Moon, both are S-U-Z-Ys. But if this happens every month, why don't we have a solar eclipse every new moon and a lunar eclipse every full moon? Because a S-U-Z-Y does not have to be a perfect alignment. The moon's orbit is tilted by about 5 degrees compared with the earth's orbit around the sun.

2:28So, most months, the moon passes a little above or below the exact line needed for an eclipse. Only during an eclipse season, roughly every six months, is the geometry right for eclipses to happen. During a solar eclipse, the moon passes between earth and the sun closely enough for its shadow to fall on earth. During a lunar eclipse, earth lies between the sun and the moon, and the moon passes through the earth's shadow. So, every eclipse involves a S-U-Z-Ys, but not every S-U-Z-Ys produce an eclipse.

3:02The same idea also appears in transits and occultations, and the observers doesn't even have to be on earth. On June 3, 2014, NASA Curiosity rover watched Mercury cross the face of the sun from Mars. It was the first planetary transit ever observed from the surface of another celestial body. S-U-Z-Ys can involve more than three objects, too. In 1894, the geometry of the solar system produced an extraordinary configuration.

3:36From Venus, Mercury would have appeared to transit the sun. At the same time, an observer on Saturn would have seen both Mercury and Venus crossing the sun. But, S-U-Z-Ys should not be confused with what is sometimes called a planetary parade. Several planets may appear to form a line across our sky because most planets orbit the sun in roughly the same plane. That aberrant line doesn't necessarily mean that planets themselves are truly lined up in space.

4:10S-U-Z-Ys also has consequences here on Earth. Around New and Full Moon, the tidal effects of the sun and moon reinforce each other, producing spring tides, when the difference between high and low tide becomes larger than average. And no, spring tides have nothing to do with the season of spring. Perhaps that's what makes S-U-Z-Y such a wonderful astronomy world. At first, it looks complicated. S-U-Z-Y-G-Y.

4:42But the idea behind it is beautifully simple. Things coming into alignment. The next time you look at a full moon, imagine the geometry. The sun lies roughly 150 million kilometers away in one direction. The moon is about 384,000 kilometers away in the other. And you are standing on the Earth that lies almost directly between them. Three celestial bodies connected by an imaginary line stretching through space. A S-U-Z-Y.

5:13A strange little word for one of the simple geometries in astronomy. Thank you for listening. This is 365 Days of Astronomy. You are listening to the 365 Days of Astronomy podcast. The 365 Days of Astronomy podcast is produced by the Planetary Science Institute.

5:46Audio post-production is by me, Richard Drumm. Project management is by Aviva Yamani. And hosting is donated by LibSyn.com. This content is released under a Creative Commons attribution, non-commercial 4.0 international license. Please share what you love, but don't sell what's free. This show is made possible thanks to the generous donations of people like you. Please consider supporting our show on Patreon.com forward slash CosmoQuestX and get access to bonus content.

6:20Without your passion and contribution, we won't be able to share the stories and inspire the worlds. We invite you to join our community of storytellers and share your voice with the listeners worldwide. As we wrap up today's episode, we're looking forward to unraveling more stories from the universe. With every new discovery from ground-based and space-based observatories and each milestone in space exploration, we come closer to understanding the cosmos and our place within it.

6:52Until next time, let the stars guide your curiosity. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe.

The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe. The Earth is a production of the universe.