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No, this topic isn't about the new "Matrix" movie! It's about a subject far more "down to Earth" than that, although perhaps similarly perplexing.

In John Duvall's most recent trivia question, he asks: "How many revolutions does the Center Wheel make in a 24 hour period?" For me, that question brought to mind a recent epiphany, which left me curious about how many other people have never actually considered the mechanics a situation we probably all assume we understand.....

The question is:

Rounded to the nearest whole number, how many revolutions does the Earth turn about its axis in one (1) solar year?

There's nothing "tricky" about the term "solar year;" that's just a "standard calendar year," which is the length of time it takes for the Earth to complete one (1) 360 degree orbit around the Sun.

Remember, all answers are anonymous, so please participate and cast a vote! If your answer turns out to be wrong, no one will ever know but you!

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PS -- If everyone enjoys this topic, I'll follow it in a few days with a similarly vexing situation about Martian time vs. Earth time.

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Steve Maddox
President, Chapter #62
North Little Rock, Arkansas
IHC Charter Member 49

Steve,

Yes, keep them coming! Can't wait to see the answer. So far only 3 others agree with me.



Andy

Member of Chapters 168 and 185.

360 = 2 (10%)
364 = 4 (19%)
365 = 10 (48%)
366 = 4 (19%)
372 = 1 (5%)

And the answer is: The 19% guys have it!

Well, at least one bunch of them does................

The reason is as follows: If the Earth maintained its orientation in space, and did not rotate at all about its axis, during its orbit around the Sun over the course of a year, the Sun would shine on all 360 degrees of the Earth's surface, thereby creating 1 "apparent day."

Since an "apparent day" is created by the orbit around the Sun, the periods of light and dark on the Earth will be affected by one complete day/night cycle per orbit. If the Earth didn't rotate at all as it orbits, there would be one "apparent day" per year, but if it rotated once annually in synch with its orbit, the same side of the Earth would always face the Sun, and there would be NO "apparent days" in a year. Alternatively, if the Earth rotated about its axis once annually in the opposite direction to its orbit around the Sun, there would be 2 "apparent days" per year.

So, by understanding that the Earth IS rotating at the same time it's orbiting the Sun, we should realize that the number of periods of light and dark (solar days) per year must actually be 1 more, or 1 less than the Earth's actual number of rotations. In order to conclusively determine which, it's necessary to know which way the Earth rotates, as well as which way it's orbiting in space around the Sun.

In reality, to an observer looking at our solar system from a point in space above the northern hemisphere of the Earth, the Earth is rotating counter-clockwise about its axis, and it's orbiting the Sun in a counter-clockwise direction. In other words, the Earth's rotation is in synch with its orbit, thereby meaning that the periods of light and dark on the surface during one complete orbit around the sun, will be reduced by 1, rather than increased by that amount. That means that the Earth actually rotates about its axis 366 times per year (well, actually about 366.25, but we were rounding to the nearest whole number).

That's is also the reason for the difference between "mean solar time," and "sidereal time." Mean solar time is the "average" length of a complete cycle of day and night on the surface of the Earth. Sidereal time is the length of 1 complete 360 degree rotation of the Earth about its axis compared to a fixed point in space, and a sidereal day is approximately 3 minutes and 56 seconds shorter than a mean solar day. In other words, a watch set to keep sidereal time, would run 3 minutes and 56 seconds per day fast, thereby accumulating a total error of 1 "apparent day" over the course of 366.25 revolutions.

To put it another way, we know that it takes the Earth 365.25 mean solar days to return to the same point in it's orbit (1 year). If a sidereal rotation period (measured in reference to the "fixed" stars) is 23 hours and 56.07 minutes, we can convert that into fractions of a 24-hour day and get 0.99727 sidereal rotation periods per 24-hour day. Then all we have to do is divide 365.25 by 0.99727 to show that there are 366.25 sidereal rotations in a year.

In a related topic, the movement of the moon around the Earth is also very interesting. Terrestrial observers always see the same side of the moon because its period of rotation is exactly equal to its period of revolution around the Earth. To the sun, and everything else in space, however, the moon rotates about its axis once every 28 days (essentially), therefore meaning that contrary to the logic of Pink Floyd, there actually is no "dark side of the moon!"

For additional reading, those interested might wish to check out the following web site: http://www.clarkfoundation.org...vondel/Extraday.html

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Steve Maddox
Past President, Chapter #62
North Little Rock, Arkansas
IHC Charter Member 49