superball Posted November 16, 2011 Posted November 16, 2011 Hi all. New to forum, my first goal is to follow the rules, and act in a respectful manor. My question is related to a torque induced precession vs. a Torque-free precession. It is said that earth is precessing as we speak. my valid reasoning is the earth axis has shifted two time in two years. This is verified by Nasa, and also an Italian research team. This statement is true, or false? My second question is if this is a fact, then does the precession follow the tourque induced precession, or the Torque-free precession? When you comment, and i hope you will, include what precession model you support.
swansont Posted November 16, 2011 Posted November 16, 2011 It's my understanding that the axis is continually changing. If you have two specific instances in mind, you should probably include a link to each example. http://maia.usno.navy.mil/whatiseop.html
superball Posted November 16, 2011 Author Posted November 16, 2011 Greetings science geeks. http://www.jpl.nasa.gov/news/news.cfm?release=2010-071 http://www.jpl.nasa.gov/news/news.cfm?release=2011-080 I have included the 2010 results, and also the 2011 results for Earth axial shift from a reliable source. This is another touchy subject, and I don't want to convince you as to the cause, only that it has happened as described. We can add more information that is scientifically sound, and elaborate on it further. A good starting point would be to add information related by other philosophers of the past. Einstein, and Galileo Galilei comes to mind. As students of life, and science I believe we could from our observation, and special study convey our teachings in a respectful knowledgeable manner. Not an easy task alone, but with help from others adding we could meet the required data needed to form a conclusive answer. The question torque induced, or torque free Precession? Another goal of this thread is to swing the vote either way, and use factual evidence, and science to do that. Please add your concerns, together we can increase knowledge that supports a solution most likely to occur during Earth precession period. peace.
swansont Posted November 24, 2011 Posted November 24, 2011 Earthquakes are internal, so there is no external torque. You redistribute mass and you will change the axis. One must note that the numbers here are from models, not measurements. They assume nothing else has happened but the motion from the earthquake. When I asked about this, my colleagues in Earth Orientation have told me that they had never measured shifts after the major earthquakes. The net effect is too small to measure. Meanwhile, the axis has shifted continually all this time. I have no clue as to why you think this is a "touchy subject"; it's actually vital for the continued operation of satellites, so that they "know" where they are and what direction they are pointing relative to the earth. Errors in that information give rise to errors in e.g. GPS positioning and timing.
superball Posted November 24, 2011 Author Posted November 24, 2011 (edited) Earthquakes are internal, so there is no external torque. You redistribute mass and you will change the axis. One must note that the numbers here are from models, not measurements. They assume nothing else has happened but the motion from the earthquake. When I asked about this, my colleagues in Earth Orientation have told me that they had never measured shifts after the major earthquakes. The net effect is too small to measure. Meanwhile, the axis has shifted continually all this time. I have no clue as to why you think this is a "touchy subject"; it's actually vital for the continued operation of satellites, so that they "know" where they are and what direction they are pointing relative to the earth. Errors in that information give rise to errors in e.g. GPS positioning and timing. Greetings all. Happy thanks Giving. I located the mix up. I thank you for the relocation of the data. Respectfully, Super-ball. Edited November 24, 2011 by superball
Guest Zachery1 Posted December 8, 2011 Posted December 8, 2011 According to my astronomy book the precession of the Earth is actually caused by the Sun and also the moon, another exoplanets have an impact but it's really small. The blueprints it has exhibits the actual precession within the other direction associated with rotation. When they talked about sidereal days versus. solar times, the sidereal day is shorter. My personal interpretation: The actual sidereal day time is smaller because Earth is turning round the Sun in the exact same path that it's revolving, so that the Earth needs to rotate much less for that superstars to be in exactly the same placement as defined by the sidereal day; if the Planet is actually revolving in the other direction the solar day time would be smaller than the sidereal day since the Earth needs to revolve less for the Sun to stay in the same placement. Textbook: Now the book additionally states that because of the precession, the sidereal 12 months is longer than the tropical/calendar 12 months. This is why the actual solstices and also the equinoxes alter over the years. My personal interpretation: The same logic applies to the year along with the day. In the same path the actual sidereal year should be smaller as the Planet needs to move slightly more to pay for that moving placement of the Sunlight (through belief) because the Sun is actually actively playing get caught up. Whilst in the opposite direction the sun's rays ought to be in the place somewhat faster, which is what we should notice. Consider all of us turn as well as center one way, and that we precess another way based on my thinking, that presents a mysterious, at least to me. Unsure if that was clear whatsoever, I would put up pictures but I can't till I've Twenty posts. But when you go to search engines and type in "sidereal versus. solar day" as well as "rotation precession" you need to get some images that look like what I'm talking about.
D H Posted March 5, 2012 Posted March 5, 2012 (edited) This post is a reply to three posts, the original post, post #2, and post #7. My question is related to a torque induced precession vs. a Torque-free precession. It is said that earth is precessing as we speak. my valid reasoning is the earth axis has shifted two time in two years. This is verified by Nasa, and also an Italian research team. This statement is true, or false? False, and it doesn't answer your homework question. You are talking about the calculated response of the Earth to two recent large earthquakes, the 2004 Indian Ocean earthquake and the 2010 Chile earthquake. The small external torques on the Earth can be ignored over the short time span of an earthquake. Those earthquakes changed the Earth's inertial tensor by a slight bit, and thus the Earth's angular velocity had to change by a corresponding tiny bit to conserve angular momentum. (Note: It is angular momentum, not angular velocity, that is conserved in the absence of external torques.) These effects are tiny, tiny, tiny. They were not observed because they were below our ability to measure them. Even if they were observed, this has nothing to do with your homework question. This was a one-time shift in orientation, not a precession or a nutation. Your homework question is more than a couple months old, so I have no qualms answering it. The principle behavior of the Earth's rotation is that of torque induced precession. It's called the lunisolar precession. Because the Earth is not a perfect sphere, the inverse square gravity of the Moon and the Sun create external torques on the Earth. Because the Earth is rotating, these external torques manifest as a precession. There are many, many terms (2,000+ terms!) in the modern description of the Earth's orientation and rotation. The largest of these is the lunisolar precession. This dominant term is huge compared to all of the other terms. So the first answer, and second, and 2,000+ answer is that it the Earth undergoes a torque induced precession. It's my understanding that the axis is continually changing. If you have two specific instances in mind, you should probably include a link to each example. http://maia.usno.navy.mil/whatiseop.html That article talks about polar wander. Polar wander is the difference between the Earth's orientation as calculated by the SOFA (Standards of Fundamental Astronomy) model and the observed orientation. The article misses the mark of answering the OP's question. It doesn't talk about lunisolar precession, or the smaller nutations that the SOFA model describes quite well. The SOFA rotation model is semi-analytic. There are some small effects that the model currently does not capture. They instead have to be captured after the fact, based on observation. The largest of these unmodeled effects is the Chandler wobble, which is a torque-free precession. It can't be modeled analytically (yet) because the Earth is not a rigid body. The Chandler wobble exhibits some weird behaviors because the Earth is instead an elastoplastic body. A little different, my vote is for torque free 'illusionary' wobble of the tilt of the Earths axis. ... This entire post was one line of nonsense followed by another. The lunisolar precession is not illusionary. It is quite real, and it is very well explained by physics. Newton was the first to give an explanation for why this well-known precession occurs. Edited March 5, 2012 by D H
zorro Posted March 5, 2012 Posted March 5, 2012 (edited) Hi all. New to forum, my first goal is to follow the rules, and act in a respectful manor. My question is related to a torque induced precession vs. a Torque-free precession. It is said that earth is precessing as we speak. my valid reasoning is the earth axis has shifted two time in two years. This is verified by Nasa, and also an Italian research team. This statement is true, or false? False. The precession of the earth is produced by the moon and sun acting on the earth's bulge in the equatorial zone. This bulge moves the center of mass away from the center of the earth thus causing a torque. http://www.math.nus....ONOFTHEMOON.htm Incidentally this precession is why the zodiac moves and we are at the "Dawning of the Age of Aquarius". http://en.wikipedia....Age_of_Aquarius My second question is if this is a fact, then does the precession follow the tourque induced precession, or the Torque-free precession? When you comment, and i hope you will, include what precession model you support. No. The precession model is shown in the reference. ...http://www.math.nus.edu.sg/aslaksen/gem-projects/hm/0102-1-phase/ORIENTATIONOFTHEMOON.htm Edited March 5, 2012 by zorro
swansont Posted March 6, 2012 Posted March 6, 2012 ! Moderator Note Precession vs motion topic from ThorHammaraxx has been split: http://www.scienceforums.net/topic/64861-precession-or-motion/page__pid__662815#entry662815
superballs Posted November 19, 2013 Posted November 19, 2013 This post is a reply to three posts, the original post, post #2, and post #7. False, and it doesn't answer your homework question. You are talking about the calculated response of the Earth to two recent large earthquakes, the 2004 Indian Ocean earthquake and the 2010 Chile earthquake. The small external torques on the Earth can be ignored over the short time span of an earthquake. Those earthquakes changed the Earth's inertial tensor by a slight bit, and thus the Earth's angular velocity had to change by a corresponding tiny bit to conserve angular momentum. (Note: It is angular momentum, not angular velocity, that is conserved in the absence of external torques.) These effects are tiny, tiny, tiny. They were not observed because they were below our ability to measure them. Even if they were observed, this has nothing to do with your homework question. This was a one-time shift in orientation, not a precession or a nutation. Your homework question is more than a couple months old, so I have no qualms answering it. The principle behavior of the Earth's rotation is that of torque induced precession. It's called the lunisolar precession. Because the Earth is not a perfect sphere, the inverse square gravity of the Moon and the Sun create external torques on the Earth. Because the Earth is rotating, these external torques manifest as a precession. There are many, many terms (2,000+ terms!) in the modern description of the Earth's orientation and rotation. The largest of these is the lunisolar precession. This dominant term is huge compared to all of the other terms. So the first answer, and second, and 2,000+ answer is that it the Earth undergoes a torque induced precession. That article talks about polar wander. Polar wander is the difference between the Earth's orientation as calculated by the SOFA (Standards of Fundamental Astronomy) model and the observed orientation. The article misses the mark of answering the OP's question. It doesn't talk about lunisolar precession, or the smaller nutations that the SOFA model describes quite well. The SOFA rotation model is semi-analytic. There are some small effects that the model currently does not capture. They instead have to be captured after the fact, based on observation. The largest of these unmodeled effects is the Chandler wobble, which is a torque-free precession. It can't be modeled analytically (yet) because the Earth is not a rigid body. The Chandler wobble exhibits some weird behaviors because the Earth is instead an elastoplastic body. This entire post was one line of nonsense followed by another. The lunisolar precession is not illusionary. It is quite real, and it is very well explained by physics. Newton was the first to give an explanation for why this well-known precession occurs. I will very carfully explain this false assumtion you claim. first you said false. and try to justify that answer by saying. qoutte "The small external torques on the Earth can be ignored" therfore you have exludid the only factor that is used to make that determination.
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