Today's Reading

I grew up hearing only a couple of stories from my grandfather's service in World War II; like many veterans, he didn't like to talk about it. Through the National Archives, I learned that his unit, Marine Aircraft Group-31, island-hopped behind the men on the front lines, moving to conquered lands one at a time to set up bombing runs for the next phase of battle in the Pacific. Through my mom, I learned that Jack wasn't able to fall asleep in his tent-covered foxholes, and that he prayed the rosary despite his terror on island after island. A devout Catholic, he taught the words to his fellow marines. Hail Mary, full of grace, he repeated, trying to drown out cries of "Americans will die!" in accented English. Stories of these Japanese threats sailing like ghosts on the night wind chilled me to the bone when I was a kid. I wish I had asked more about them. And I wish I got to tell Jack, before he died in 2010, that he had the Moon to blame for the marines' losses at Tarawa.

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Every day, on every coastline on Earth, the tide changes the threshold where the land meets the sea. Boats in a harbor rise and fall against their docks as the day wears on. Beaches widen and narrow, and kelp, shells, or other ocean dregs left by receding tidewaters dry in the sand, far from lapping waves.

The tide ebbs and flows because of the Moon's gravity and, to a lesser extent, the Sun's. As the Moon moves around Earth, the two bodies tug on each other. The side of Earth that is closest to the Moon feels the tug a little more strongly, and the Moon pulls water toward itself, creating two bulges [*1] in the world's oceans. The bulges create the high tide, which originates in the ocean and progresses toward the coasts. Twice a month, the Sun adds some tidal heft, as well. When it is lined up with the Moon, causing either a full Moon or an invisible new Moon, the Sun's gravity amplifies the bulging effect. This forms what are known as spring tides, and these bring higher high tides and lower low tides.

Seven days later, when the Moon is not lined up with the Sun but set apart at a ninety-degree angle, it looks half full. [3] We call this first quarter or last quarter. The Sun's gravity has less of an impact on the tides and produces what is called a neap tide. The high and low tides are less extreme at this point in the month.

Earth's geography also plays a role in how the water comes in. The continents change the tide's flow, and the depth of a shoreline changes how quickly the tide will rise or how slowly it will fall. And the Moon's location in orbit around Earth changes its gravitational pull, too. The Moon, like all celestial bodies, does not travel in a circle but in an ellipse, something that, as we'll see later, we learned from a seventeenth-century German astronomer obsessed with the Moon. The point on its orbit where it is most distant from Earth is known as apogee, and the point where it is closest is known as perigee. Three or four times a year the perigee coincides with a full Moon, which astrologers in the first part of the twenty-first century C.E. dubbed a "supermoon." The closer Moon yields exceptionally high and low tides. The more distant, apogee Moon—call it a micromoon—is slightly smaller in the night sky and has a weaker pull. But even a faraway Moon exerts a powerful influence over Earth.

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The marines planned their invasion during a neap tide and couldn't understand why the tide not only failed to rise enough but did not rise at all, for almost two days. The "dodging tide," as war chroniclers later called it, lay low over the Tarawa reef because the Moon was at apogee, its pull weak because it was so far from Earth. November 20 was one of only two days in 1943 to experience an apogean neap tide. Before the satellite era, and certainly before the marines captured the island and measured its geography, there was no way for American military planners to have known how dramatically this lunar alignment would affect the tides in Tarawa.

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Despite the carnage, marines kept coming ashore, and the bombs kept falling. After three days of fighting, the waters finally returned and the marines took the atoll, but the devastation was complete. Americans back home were outraged, wondering how capturing such a tiny island could have led to such casualties.

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My grandfather's unit arrived at Tarawa on New Year's Eve 1943. By then, the Allies controlled the island and the Navy Seabees had cleared the beaches of the bodies and the palm trees. Private First Class Corcoran continued his work, equipping planes with bombs for the next stage of the multipart Pacific plan. The Moon was four days old when he arrived at the battered atoll. It hung in the evening sky like a scimitar, like a scythe, like the horns of a bull. It was small enough that you could easily miss it, until it snuck up on you.

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