Answer Man

Here’s how the moon works at the North Pole

What is the harvest moon?

The "harvest moon" is the full moon closest to the autumnal equinox, the beginning of northern fall.
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The "harvest moon" is the full moon closest to the autumnal equinox, the beginning of northern fall.

Q: North of the Arctic Circle, the sun disappears for weeks or months at certain times. Does the moon disappear in the same way during this time also?

L.T., of Belleville

A: Yes, the moon’s behavior near the poles is just as loony as the sun’s — but for shorter periods because of reasons I hope will become clear to you. It’s a little hard to explain without diagrams, but let me try:

The main reason for this oddity is that if you’d be on the sun watching the Earth making its yearlong orbit, you’d see that our planet is not positioned straight up and down relative to its orbital plane. In other words, if you can imagine the track of the Earth’s orbit being marked out on an immense sheet of paper, the North and South poles are not perpendicular to that sheet of paper.

Instead, the poles are tilted at a roughly 24-degree angle — and they retain that tilt as the planet circles the sun. What that means is this: If you were at, say, the North Pole at the summer solstice in June, you would see the sun at its highest point in the sky — 23.5 degrees above the horizon — because that’s the day the pole reaches its maximum tilt toward the sun during our annual orbit.

For the next three months, you’d see the sun 24 hours a day as it traveled in a circle around the sky, but it would ever so gradually sink lower in the sky because the Earth’s tilt would be moving the pole away from the sun. When we mark the start of autumn in St. Louis, the polar bears are experiencing sunset followed by three months of increasing darkness when the sun is never seen. Finally, on the winter solstice, the North Pole is experiencing maximum darkness because the pole’s tilt has now reached its maximum away from the sun.

Then, everything is reversed. On the spring equinox, Santa is watching the year’s only sunrise, and for the next three months, the sun slowly rises in the sky until it again reaches its maximum height on the summer solstice only to start the cycle over again. To make a long story short, North Polers basically see the sun all the time for six months before it disappears for six months. (The same is true at the South Pole except you have to remember that the seasons are reversed in the Southern Hemisphere.)

So, you do have the right idea about the moon, but the wrong time frame. It takes the Earth a year to orbit the sun, so you have six months of light followed by six months of dark. But the moon takes only roughly 28 days to orbit the earth. So, again because of the Earth’s tilt, people at the poles get a regular diet of seeing the moon constantly for two weeks before it disappears for two weeks.

Moreover, lovers who want to take advantage of a full moon would have a rough time because the phase of the moon you would see for long periods differs as the year progresses. At the beginning of summer, when the sun is highest in the sky, the moon would be up for approximately the two weeks closest to the new moon. By the time fall comes around, the moon would be showing its face for the two weeks closest to last quarter before again disappearing for two weeks.

Unfortunately, romance would have to come during the coldest part of the year — winter — when the moon would pop up for the two weeks closest to the full moon. But by spring, skywatchers would see the moon only for the two weeks closest to the first quarter before, like the sun, starting the cycle all over again. So, it’s six months light six months dark for the sun and two weeks light followed by two weeks dark for the moon.

We can only wonder what life would have been like here for Lon Chaney.

Today’s trivia

Where would you go to see dozens of mounds constructed by prehistoric Native Americans in the shape of animals, birds and reptiles?

Answer to Saturday’s trivia: As best as historians can figure, Timotheus Ritzsch started the world’s first daily newspaper on July 1, 1650 — the Einkommende Zeitungen ( the “coming-in” or “incoming” newspaper) in Leipzig, Germany.

Roger Schlueter: 618-239-2465, @RogerAnswer

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