In the Tom Clancy novel, The Hunt for Red October, a Russian submarine captain attempts to defect by piloting his sub to the U.S. After avoiding the Russian fleet, the captain heads for Pamlico Sound, North Carolina. Unfortunately, Ocracoke inlet, the narrow entryway into the Sound, is shallow, so the captain must wait until the tide is highest. The author states that it is a clear, but moonless night (i.e., a New Moon), and then correctly gives the time of entry into the sound. When is the first time that the Red October can enter Pamlico Sound?
A) Around midnight
B) At dawn
C) Near dusk the next day
D) 1 week later, around midnight
E) 1 week later, around dawn
A) Around midnight.
The tides are due to the interaction of the Earth's water and the moon's gravity. Basically, the moon is "sucking" the water up off the surface of the Earth. This is strongest in the area beneath the moon, wherever that happens to be. Because of the way that gravity works, this distorts the Earth's water into a roughly oval shape. This means that there is also a high tide on the opposite side of the Earth from wherever the moon happens to be.
A New Moon means that the Sun and moon are in the same part of the sky; thus, the moon will be over the opposite side of the Earth around midnight, and create a high tide. It should be noted that the midnight tide will not be as high as the other one, due to gravity diminishing over distance. This is partially compensated by a "spring tide", as mentioned in the novel; this is the combined effect of the Sun and moon's gravity.