This is a further article in my occasional series about coal, engines and energy, heat and thermodynamics. In this article I am going to show you how to push the Moon further away using some very basic machinery invented by 19th century scientists and engineers. Yes! Really!
This Earth of ours is so huge in scale compared to our puny bodies. How could it be possible that by our ordinary actions we could alter the whole Earth climate system?
Let me try to give you a perspective on that, at the scale of a classroom globe:
If we were to wipe a wet paper towel across a twenty-inch globe, the film it leaves behind would be too deep to properly represent the depths of earth's oceans.A similar argument holds for the atmosphere.
Razor-thin Films: Earth's Atmosphere and Seas
Now, let us agree that at the scale of a twenty-inch globe, the oceans and atmosphere seem tiny and insignificant by comparison with the whole planet. Of course, on that scale, humans are entirely invisible, so let's ignore them for now.
Enter the Moon:
At the same scale as before, the Moon is a five-inch globe about 55 feet away from the Earth. Note that these are round figures used to conjure up a mental image and should not be taken to show an exactness of scale. That said, we can determine the real distance of the real Moon to a very high degree of accuracy.
Now, let us agree that although the Moon is smaller than Earth, it is a lot bigger than the Earth's oceans and atmosphere combined. A question: could the ordinary activities of modern humans affect the Moon in any way whatsoever?
The answer to that question, as I intend to convince you in this article, is a resounding "Yes!".
The Earth-Moon Tide System
Any ordinary person can observe that the phases of the Moon and the tides seem to follow the same clock. Perhaps many a peasant, in an idle moment has speculated that the Moon might be the cause of the tides. In fact, the Moon is the major contributor to the tides, with the Sun being the other contributor.
By a gravitational mechanism which need not be explained here, the Moon by its very presence modifies the Earth's gravitational field. Because the Earth rotates, the high-low tidal zones do not stay where the Moon's influence put them. This causes water to fall in some places and to rise in others, flowing from place to place in tidal streams.
When water flows it becomes warm from turbulence and from the friction or drag against any surface or obstacle it encounters. In a very real sense, the energy of motion, the kinetic energy put into the water by the Moon, is lost as waste heat.
Not only does the Moon dump heat into the oceans: it dumps it into the land as well. Although we think of rock as solid, on the scale of the whole planet, the outer crust is quite flexible. There are tides in the rocks, as well as in the oceans. We don't feel these tides because the motions are tiny compared with the oceans.
George Darwin, son of the more famous Charles Darwin made an extensive study of the tides and attempted to show the age of the Moon through his tide theories. He reasoned that the dumping of heat into the land and the oceans due to the Moon's gravitational action must have some effect on the Moon itself.
The tidal drag converts energy into heat. The energy comes from the Earth's rotation, so the Earth is actually slowed down by this drag. To complete the energy balance in celestial mechanics, the Moon is receding: moving extremely slowly away from the Earth.
Working backwards from the recession rate George Darwin concluded that at one time the Moon must have been in contact with the Earth itself. Perhaps the Moon was formed when a mass of magma split off from a young Earth? According to this fission theory, the age of the Earth-Moon system was at least 56 million years.
Thus did the younger Darwin reinforce his father's theories by showing a geological time-scale which might fit the theory of evolution.
The modern accepted theory of the Moon's formation, the giant impact theory, makes the Earth about 4.5 billion years old. That figure is supported by geological findings.
One small laser reflector for mankind
The Apollo 11 astronauts left behind a laser reflector aligned with Earth. It is the only Apollo 11 experiment still operational today.
Source: NASA Apollo Archive
That laser reflector, with others, is used to measure with an extraordinary accuracy the distance from the Earth to the Moon. The laser experiment shows that by dissipating heat, mainly in the ocean tides, the Moon is receding from Earth at a rate of 38 mm per year.
The Human Scale
Let us now bring humans back into the big picture. What happens when you convert tidal power into electrical power?
Whatever means we use to convert one form of energy to another, there will always be losses in the system. All electrical power, however it is used, eventually ends up as heat in our environment. That makes our energy calculations very easy indeed.
The tides dissipate roughly 3 Terawatts of energy annually. In the year 2002 the USA used 3.3 Terawatts. Suppose that, through the use of turbines of the type that the Victorians could have built, the USA now extracted 3 Terawatts of tidal energy annually. We will take that figure as a total of useful electrical energy + system losses. An exact breakdown of the figures is not required.
Tidal energy is most odd. It gives an appearance of an infinite resource. Every Watt of power humans get from the tides is added to the planet's tidal energy budget. That is because our energy-extraction machines add to tidal friction.
Conclusion:
If 3 Terawatts of energy could be extracted from the Moon via the tidal mechanism, the Moon's rate of recession would double. The population of the USA, or any part of the Earth's total population, just by consuming tidal electricity in a large enough quantity can move the Moon an extra 38 mm every single year! Oh, yes! And slow down the Earth's speed of rotation - the length of the day - by an extra 20 microseconds every day!
Our 19th century forebears could easily have grasped the idea that extracting power from the tides is equivalent to extracting power from the Earth-moon system.
Given that the Earth's oceans and atmosphere taken together make up a far smaller mass than the Moon; given the above proof that puny humans can easily affect the moon at a distance of about 239228 miles, or 385000 kilometers; why can some puny humans not accept the less remarkable fact that we are affecting our puny oceans and atmosphere?
[edit] - '20 microsecond every year' corrected to 'an extra 20 microseconds every day.'
(Thanks to Swans on Tea for spotting the error.)
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Recommended for further reading:
http://www.science20.com/rock_whacker/blog/earths_first_rocks
Razor-thin Films: Earth's Atmosphere and Seas
http://www.psi.edu/projects/moon/moon.html
http://science.nasa.gov/headlines/y2004/21jul_llr.htm?list736830
http://science.nasa.gov/headlines/y2004/21jul_llr.htm?list736830
http://en.wikipedia.org/wiki/Tidal_acceleration
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