Just Because: Of Moons, Tides, And Floods

By Jack Forster

Headline image, Vacheron Constantin Les Cabinotiers Celestia, 2017.

When you live in New York, it’s easy to forget that you’re living in a city right on the water’s edge – many New Yorkers can go months without seeing the water, despite the fact that Manhattan is surrounded by it and every borough at least borders a body of water. We were reminded of our proximity to the Atlantic vividly in 2012, when a storm surge from Superstorm Sandy combined with a high tide to flood lower Manhattan and knock out power to the area, as well. My apartment’s in a building just a few blocks from the East River and we went from “desirable waterfront location” to “BYO Boat” in just a few hours, and it took a week before the lights went on again.

This is all by way of saying that while the tides, and the position of the Moon relative to the Earth and Sun, can seem a little abstract to most of us, they are some of the most powerful and irresistible forces on the planet. Watches that show the positions of the Earth, Moon, and Sun relative to each other are the key to understanding how the tide cycles work and how watches that actually show the high and low tides each day function.

To start, there’s the ordinary moonphase complication. The Moon orbits the Earth once every synodic month (the amount of time it takes for the Moon to return to a line drawn between the Sun and the Earth) and while the length of the synodic month varies throughout the year due to periodic variations in the Earth’s orbit, the average is about 29.53059 days. The Moon always shows the same hemisphere to a viewer on Earth and detailed moonphase displays can show the conspicuous lunar “seas” as well as features like the enormous Tycho impact crater.