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hippy4christ
Skeptic Friend
193 Posts |
 Posted - 07/17/2003 : 15:35:37
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Hi
How come the moon's rotation is so perfect that it always shows one side? How could something like that just happen?
Hippy
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Faith is believing what you are told, whether it's by a priest or a scientist. A person's scientific beliefs are ones based on personal observation and experimentation.
Lists of Logical Fallacies |
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Slater
SFN Regular
USA
1668 Posts |
Posted - 07/17/2003 : 15:58:45 [Permalink]
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| What's so odd about it? Mercury does the same thing |
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Randy
SFN Regular
USA
1990 Posts |
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NubiWan
Skeptic Friend
USA
424 Posts |
Posted - 07/17/2003 : 18:27:23 [Permalink]
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| Well OK, will bite, how come and how did it happen? |
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ktesibios
SFN Regular
USA
505 Posts |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 07/17/2003 : 19:43:14 [Permalink]
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quote:
Originally posted by ktesibios
Incidentally, the moon's rotation isn't quite "perfect". The moon's rotational axis wobbles slightly with respect to its orbital plane; as a result, even before spacecraft were able to send back images of the parts of the moon's surface that are hidden from Earth, astronomers had been able to map approximately 59% of the moon's surface.
And here's a simple animation of the moon's libration...
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"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
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hippy4christ
Skeptic Friend
193 Posts |
Posted - 07/18/2003 : 15:02:22 [Permalink]
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Okay, I guess I was assuming that the rotation had been constant. Thank you.
Hippy |
Faith is believing what you are told, whether it's by a priest or a scientist. A person's scientific beliefs are ones based on personal observation and experimentation.
Lists of Logical Fallacies |
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hippy4christ
Skeptic Friend
193 Posts |
Posted - 07/18/2003 : 15:09:22 [Permalink]
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On another note, does anyone know how fast a magnetic field decays? Another argument I've heard used is that if the earth were 14 billion years old, its magnetic field would have decayed by now. I have no knowledge of this, but does anyone else?
Hippy |
Faith is believing what you are told, whether it's by a priest or a scientist. A person's scientific beliefs are ones based on personal observation and experimentation.
Lists of Logical Fallacies |
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Phobos
New Member
USA
47 Posts |
Posted - 07/18/2003 : 16:12:47 [Permalink]
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quote:
Originally posted by Slater
What's so odd about it? Mercury does the same thing
Note that most of the other moons in the solar system have the same situation.
excerpt from http://www.seds.org/billa/tnp/luna.html
quote:
The same thing has happened to most of the other satellites in the solar system. Eventually, the Earth's rotation will be slowed to match the Moon's period, too, as is the case with Pluto and Charon.
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Phobos
New Member
USA
47 Posts |
Posted - 07/18/2003 : 16:19:31 [Permalink]
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quote:
Originally posted by hippy4christ
On another note, does anyone know how fast a magnetic field decays? Another argument I've heard used is that if the earth were 14 billion years old, its magnetic field would have decayed by now. I have no knowledge of this, but does anyone else?
Hi hippy4christ
For starters, the Earth is about 4.5 billion years old. It's the universe that is about 14 billion years old. (I know...honest mistake)
I'll have to check some references for the decay time of a planetary magnetic field. I doubt that is an easy answer (depends on planetary size, composition, rotation, etc.). |
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Darwin Storm
Skeptic Friend
87 Posts |
Posted - 07/18/2003 : 16:45:07 [Permalink]
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quote:
Originally posted by hippy4christ
On another note, does anyone know how fast a magnetic field decays? Another argument I've heard used is that if the earth were 14 billion years old, its magnetic field would have decayed by now. I have no knowledge of this, but does anyone else?
Hippy
Magnetic fields don't really decay. Current theory holds that the earth's magnetic field is generated a molten core of various metals, that are rotating a different speed then the crust. It essentially makes the earth a huge spinning magnet. However, the molten core is fluid, and thus can shift. It is believed that occasionally the magnetic pole can reverse itself. However, while the process is not super commmen, it is believed to have occured several times in the past. As the molten core shifts, the strenght of the filed may weaken. As it switches, the magnetic strength is believed to drop off greatly, before essentially flip-flopping, at which point the magnetic filed strenght should return to normal.
I have seen some research on how the magnetic north pole is actually wobbling, and has been drifting south. It could either be a minor disturbance of the core, and thus a tempory shift, or it could be the prelude to a magnetic reversal. Either way, the erratic shift should cause some weakening the field, according to current theory.
By the way, if you are interested in magnetic fields, look up some research on the sun's magnetic field. Supposedly, its field is so strong it acts a sort of a huge force field for our solar system, and diverts alot of dangerously charged cosmic particles and radiation. |
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walt fristoe
SFN Regular
USA
505 Posts |
Posted - 07/18/2003 : 17:06:45 [Permalink]
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quote:
Originally posted by Randy
And here's a simple animation of the moon's libration...
Hey, thanks for that image Randy! That's pretty cool, and I've never seen it before. |
"If God chose George Bus of all the people in the world, how good could God be?"
Bill Maher |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 07/18/2003 : 17:58:20 [Permalink]
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quote:
Originally posted by hippy4christ
Okay, I guess I was assuming that the rotation had been constant. Thank you.
Hippy
Hey Hippy,
Just to add, -- Earth does a similar little wobble/libration "dance" in tune, so to speak, with the moon. As far as I know, so does the Sun and other planets, along with the entire solar system. Everything just spinning in a seemingly wimbly, wambly, wobbly sort of way, - in relation to one another; sort of like a kid's spinning top that's starting to loose spin. Course, the whole orchestrated event is ridigly governened by the laws of gravity. It ain't nuthin' bud-da thing.
Here's a bit more from another astronomy site:
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Libration in latitude is due to the Moon's axis being slightly inclined relative to the Earth's. Each of the lunar poles will appear to be alternately tipped slightly toward the terrestrial observer over a roughly four week cycle.
Diurnal libration is due to the observer being on the surface of the Earth, up to four thousand miles to one side of the Earth-Moon axis, a significant proportion of the centre-to-centre distance. The difference in perspective between the rising and setting of the Moon appears as a slight turning of the Moon first to west and then to east.
Libration of longitude is an effect of the Moon's varying rate of travel along its slightly elliptical orbit. Its rotation on its own axis is more regular, the difference appearing again as a slight east-west oscillation.
Although the Moon always presents the same face towards the Earth, due to its rotation and revolution being locked to the same period, the combined effect of these different librations allows us over time to see some 59% of its surface.
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quote:
Originally posted by walt frisco
Hey, thanks for that image Randy! That's pretty cool, and I've never seen it before.
Your welcome, Walt. I found it thru an astronomy webring some time ago. You can see the Moon's visible size change between its perigee (farthest) and apogee (closest).
Here's a larger gif, plus added bonus of a lunar sunrise..
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"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
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walt fristoe
SFN Regular
USA
505 Posts |
Posted - 07/19/2003 : 17:00:16 [Permalink]
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What can I say Randy?
Awesome! |
"If God chose George Bus of all the people in the world, how good could God be?"
Bill Maher |
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Randy
SFN Regular
USA
1990 Posts |
Posted - 07/19/2003 : 18:44:27 [Permalink]
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I slowed the animation a bit. Gives a better study, I think....
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"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
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jmcginn
Skeptic Friend
343 Posts |
Posted - 07/21/2003 : 10:38:11 [Permalink]
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quote:
However, while the process is not super commmen, it is believed to have occured several times in the past.
Actually it is quite common at least in the geological time scale and appears to flip on a regular basis.
http://image.gsfc.nasa.gov/poetry/ask/amag.html for a full list of Q&A
and
http://image.gsfc.nasa.gov/poetry/ask/a10866.html for a detailed answer (about 60 reversals in the last 20 million years) with reversals occuring on average every 100,000 years.
quote:
I have seen some research on how the magnetic north pole is actually wobbling, and has been drifting south.
Yes this is quite true and there is enough sedimentary data to track its wobbling over the last 40,000 years or so. In fact in recent sediments dating can be done by how the sediments are aligned pointing to where the magnetic pole wobbled.
quote:
By the way, if you are interested in magnetic fields, look up some research on the sun's magnetic field. Supposedly, its field is so strong it acts a sort of a huge force field for our solar system, and diverts alot of dangerously charged cosmic particles and radiation.
Also of interest in the link above in relation to the sun's magnetic field is that it reversals are very short, only 11-12 years. Hey I learned something today :> |
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