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The Moon: Earth's Sneezeguard
Mandi Walls writes "SF Gate is running an article about looking on the moon for pieces of Earth that may have been knocked into space by collisions with asteroids, etc. The article claims the guys responsible for the idea came up with it while stuck in traffic. They were probably digging for change for a toll in the seats."
Salad Bar?
Let's just wait for these Earth rocks on the moon to be sent back to Earth by the same process. :)
In fact, after a little searching I found this at NASA:
A few more links: Perty image and more detailed explanation; a google search on the topic.
the article says that the guys thought of this while stuck in traffic one day a few years ago. Fundamental ideas and concepts sometimes do get thought up while the person is in an odd situation, iow not the place one would expect such a solution would be thought of.
examples: Newton determined that buyuncy (sp?) exists because he felt lighter in weight after getting into the bathtub one morning. This helped him solve a problem given to him by the King who said his new crown felt lighter than the previous. The story goes that Newton ran through the streets nude shouting "Eureka!! Eureka!!" His discovery helped him determine that the crown was not 100% gold, but rather some other metal with a layer of gold on the exterior. This was determined before he tore the crown open to confirm his theory.
example 2: The guys who found a key exchange algorithm for quantum encyption keys. They had a chance meeting with each other at a train station after one of their trains ran late. Standing on the platform, they had, as Simon Singh put it in his book The Code Book, "one of those eureka moments" where they figured out the trick needed.
If the moon is receding, something is pulling it away; you can't "back calculate" that because it would be some kind of idiosyncratic effect. By default, the moon would simply spiral into the earth.
Well, if you consider that the Earth/Moon system is not the only gravity well in the solar system, you might come to the conclusion that the Sun and/or Jupiter and/or any other massive object might have a cumulative pulling effect. Because the orbits and masses of these objects is known, it would be relatively easy to calculate this effect.
To address two different points in these messages:
- Why would the moon "spiral into the earth" by default? There's nothing moving it in either direction in an ideal system.
- The moon recedes from Earth because of "tidal drag". The moon and the earth each deform each others' surfaces (creating the tides that we know so well, among other things). The net effect of this is that if one or both of the bodies are spinning, you get angular momentum transferred. The earth's rotation slows down, and the angular momentum the earth loses goes into the moon's tangential motion about the earth, which pushes it into a higher orbit.
This is what caused the moon to be tidally locked to us in the first place (i.e. always showing the same face to us).
We can calculate the rate of momentum transfer, but I don't have the numbers for that off the top of my head.
2) the Earth's rotation is slowing.
These phenomena are connected. The speed of the Moon orbiting around the Earth is increasing as the Earth's angular momentum is transferred to the Moon's orbital kinetic energy.
What's happening is the Earth-Moon system is connected by gravitational force which distorts the shape of the oceans from being roughly spherical into being a bulge pointed towards the Moon. The Earth rotates faster than the Moon orbits around the Earth. This means the tidal bulge is always being pulled forwards because of the frictional forces between oceans and Earth. This slight shift in the bulge slightly alters the overall gravitational field of the Earth thus pulling on the Moon and weakly accelerating it in its orbit to higher speed and causing it to drift slowly away from Earth at about 4cm/year. This is also explained well here.
Will
Why oil price increase equals economic trouble (Score: Interesti
...Greek for, "This bath is too hot." - Dr. Who
If I had moderator points that would definitely have got an "informative" but I guess there are a couple of points I can add to justify a response.
Firstly, it is rather sad that such a basic yet interesting fact as this angular momentum transfer seems to be completely missing from the standard education curriculum.
Secondly, I've been trying to get to first base in compiling some data on the energy storage and rate of use in major planet-wide systems (down to, say, the gravitational potential of elevated water and ice stores) but am stuggling to find clear data.
Even in such an obvious area as total solar radiation the ratio between what the Sun is claimed to radiate (386 billion billion megawatts) and what the Earth is claimed to receive (4.4 x 1016 watts) seems to fly in the face of simple geometry which seems to me should have the earth intercepting one part in 1.1 billion of the Sun's radiation.
Digging for data on other energy systems, there is a total mess of approaches and even units used by different specialties that are going to make even a basic comparison table hard work to draw together, unless of course I am willing to become a "Creation Scientist".
-- Our systemic servants do not good masters make.
Even in such an obvious area as total solar radiation the ratio between what the Sun is claimed to radiate (386 billion billion megawatts [seds.org]) and what the Earth is claimed to receive (4.4 x 1016 watts [nasa.gov]) seems to fly in the face of simple geometry which seems to me should have the earth intercepting one part in 1.1 billion of the Sun's radiation.
;).
:).
The number I keep hearing for solar energy flux is between 1 and 1.5 kW/m^2 at the Earth's distance from the sun, which gives between 1.5e17 and 2e17 watts for the whole earth. The amount that reaches the surface is less, and the amount that could be captured by any practical harnessing scheme would be much less, but I digress. This is roughly in line with the NASA numbers.
At this flux, total solar energy output is between 3e23 and 4e23 watts. SEDS claims 4e26, so they probably switched "million" and "billion" somewhere.
Digging for data on other energy systems, there is a total mess of approaches and even units used by different specialties that are going to make even a basic comparison table hard work to draw together
What gets me is conversion to/from ergs with old articles
My suspicion is that solar power flux dwarfs most of the mechanical potential energy stored on Earth's surface features. Earth's angular momentum holds one heck of a lot of energy, though, as does that of the earth-moon system, so tidal will work for quite a while.
Wind is recycled solar. Ditto anything involving growing crops.
Energy stored in wind at a given time can be estimated by assuming an average velocity (maybe look up the speed of the trade winds). Mass of the atmosphere is easy to calculate (about 10 tonnes per square metre of the earth's surface; it's just the atmospheric pressure).
I have no idea how much energy is stored in hydrocarbon reserves. You can probably get an upper limit by looking at the elemental abundance of carbon in the earth's crust, and assuming that the upper km is accessible.
The other big source is geothermal, which is driven by radioactive decay in the earth's core. I'm afraid I don't have numbers for the energy flux offhand, but it should be straightforward to calculate. Anything that's still fissioning now will have a long enough half-life to last for billions of years more.
Fissionables on the earth's surface will be dwarfed by geothermal, which effectively makes all radioactives on the planet available for harvesting (albeit over quite a long time).
Good luck with your search, in any event