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Converting RA/Dec to earth centered coordinates? (Correction)
How many times will this verbose boor receive a polite response to his
deliberate idiocy? 1000 times. 10,000 times? Do you value your time, or ours, so cheaply? Forget the telescope. The deliberate cretin does not believe in telescopes. Magnification is the work of the devil. He made that up too. Tie the dunce firmly to a post with another tall, slender post set out some distance before him. Place several accurate stop watches, with seconds indication, just out of reach in front of him. Point out a bright star accurately aligned with the distant post from his fixed position. Now start the watches. Ensure he understands which pattern the star belongs to so there is no confusion next time around, and the next. Particularly when he is tired, bored, hungry and thirsty. Martyrs are two a penny and no more valuable to anybody sane on this earth. Now leave him there for as long as it takes. He may be instantly released, at any time, only on admission of his deliberate stupidity and endless trolling. His freedom lies entirely in his own hands. No further explanations are remotely necessary. Nor required. The stars do not lie. They have not lied since classical times when the Earth's rotation was judged to be 23:56:04 within the tolerance of their instrumentation. If you want to make it more entertaining you could offer food and drink at 23:56:04 precisely. He has only 3 minutes and 50 seconds to accept the meal but not a moment longer. Acceptance of the meal will be an open admission of his own deliberate idiocy and his wasted years of pathetic, infantile trolling. Refusal will mean another 23:56:04 tied to his dunce's post before the meal is offered again. He will then have another 3 minutes and 50 seconds to accept or decline the meal. Do the stars lie? You can take a boor to knowledge but you cannot make him think. http://en.wikipedia.org/wiki/Earth%27s_rotation |
#12
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Converting RA/Dec to earth centered coordinates? (Correction)
On May 6, 5:59*am, oriel36 wrote:
On May 6, 1:34*am, Bill Owen wrote: This absolutely blows me away that guys with NASA and Harvard monikers attached to their posts are no better or worse than the other nuisances ,it takes literally nothing to look at a telescope tracking stellar circumpolar motion and conclude that the axis of the rotation is not the telescope sweeping out the rotation of the Earth as it turns around its mount but merely a homocentric convenience where the number of returns of a star follow days and dates of the calendar system.References for geocentricity don't even exist as the Earth's dynamics are split into daily and annual cycles,normally referenced to the central Sun as cause and effects,this business of dumping everything into Right Ascension is generating horrifying results and moreso in that your kind insist that it is the basis for both daily and orbital dynamics. Not enough intelligence to pull back,not enough courage to move in a direction to set the matter straight,the result is ignominy for everyone and make no mistake about it,despite the carefully constructed language that operates on the basis of Ra/Dec reckoning,it still amounts to a civilization ending conclusion that a 24 hour rotation does not match a daylight/darkness cycle.You have no idea of the implications attached to the attempt to create an imbalance between primary cause and effect but I assure you that I do. |
#13
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Converting RA/Dec to earth centered coordinates? (Correction)
On Mon, 02 May 2011 18:48:38 -0700, "W. eWatson"
wrote: On 5/2/2011 2:28 PM, Steve Willner wrote: In , "W. writes: My xy plane is in the plane of the equator, and its projection into the sky represents the celestial equator. Declination is measured +/- from the celestial equator to each pole along great circle lines that pass through each pole. Somewhere on the celestial equator is point from where RA is measured. To go from RA/Dec to an x,y,z unit vector is just simple trignometry: x = cos(dec)*cos(RA) y = cos(dec)*sin(RA) z = sin (dec) Make sure to convert RA/dec to degrees or radians (whatever units your calculator or program uses). It's easy to forget to multiply hours by 15 to get degrees. The zero point of RA is the place where the ecliptic and celestial equator intersect with the equinox heading north. Both this zero point and the location of the celestial poles changes with respect to the stars because of precession. If you want a _current_ x,y,z unit vector, you need to start from current RA/Dec coordinates rather than coordinates at a standard "ecliptic and equinox" (B1950 or J2000). The Meeus book will tell you how to do that calculation. Ah, the obliquity of the ecliptic (e) is what I need. Don't see why you need that. Did you mean ecliptic coordinates rather than celestial? Whoops, I posed the question backwards. I have the x,y,z coordinates of a vector and I want to convert them to ra/dec. In a unit sphere I think of z as pointing through the north pole, x pointing south through 1,0,0, and y pointing east through 0,1,0. In my case, precession does not enter into matters. I'm constructing a simulation that is mostly grounded in az/el and lat/lng. I wrote a program that produces the path of a fake meteor moving in a straight line. Time is not yet useful as a consideration yet. The direction of the line points to the radiant point in the sky. Meteors lie on a great circle, hence pass their plane passes through the earth's center (spherical earth). My program has not yet needed ra/dec, which is usually the measure of the radiant point in the sky and is given in ra/dec. However,I have the data from a similar program, and they provide the radiant as ra/dec. internally, my program seems sound when I sort of run it backwards. I get agreeable results. I want to see if the independent source and I agree. You may never be happy with your equations as they stand because you have chosen the X axis to point south and Y pointing east, so the positive values of X will run backwards i.e. down. You can still have a right-hand system with X pointing east and Y pointing north. Then envision a pitch over yaw gimbal set, like a theodolite, to do your pointing and let Y be the "look vector". Now you can read the declination D on the pitch axis and right ascension A on the yaw axis, CCW positive. X and Y will then "lay out" normally. This gimbal set P/Y is the only one that is congruent to the longitude latitude geometry. The XYZ coordinates are the result of swinging the "look" vector, y = (010), through D1 (declination on X axis) In combination with swiveling R3 (right ascension on Z). The validity of the physical result is ensured by the rigidity of the gimbal set where the concept of temporal order is trivialized. It is only in matrix multiplication that order is important. If we use row vectors we get U2D1A3 = V, U2 = (010) or with column vectors V = A3D1U2 The result I get is X = - cosDsinA Y = cosDcosA Z = sinD Thus you can invert for angles A = atan(-x/y) D = asin(z) I am quite certain that you need to follow this scheme if you want to stay out of trouble. John Polasek |
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Converting RA/Dec to earth centered coordinates? (Correction)
On May 6, 11:06*pm, John Polasek wrote:
Then envision a pitch over yaw gimbal set, like a theodolite, to do your pointing and let Y be the "look vector". Now you can read the declination D *on the pitch axis and right ascension A *on the yaw axis, CCW *positive. X and Y will then "lay out" normally. This gimbal set P/Y is the only one that is congruent to the longitude latitude geometry. The XYZ coordinates are the result of swinging the "look" vector, *y = (010), through D1 (declination on X axis) In combination with swiveling R3 (right ascension on Z). The validity of the physical result is ensured by the rigidity of the gimbal set where the concept of temporal order is trivialized. How sweet,there is a good reason why I have yet to find individuals capable of discussing the issue of planetary dynamics insofar as empiricists insist on using the daily rotational characteristics to define both daily and orbital characteristics off Right Ascension.When I see the time lapse footage of Uranus where daily rotational characteristics to the Sun run North/South and parallel with the Equatorial rings,at least to the viewers perspective,while the planet turns to the central Sun East/West on a separate travelling axis - http://astro.berkeley.edu/~imke/Infr..._2001_2005.jpg The necessity of two separate cycles,one where a planet turns to the central Sun in terms of intrinsic rotation and variations in latitudinal speeds and set off against the orbital turning to the central Sun requires clear thinking.I know none of you can compete and I suggest you do not bother,interpretative astronomy is at a compositional level rather than a commentary level and however colorful you write your descriptions to impress an audience,it is charming to me for all the wrong reasons. |
#15
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Converting RA/Dec to earth centered coordinates? (Correction)
Ultimately this is all forensics and no matter how interesting it may
be,sort of like stopping an intellectual runaway train,it doesn't actually address the many positives that arise from disentangling the Earth's daily and orbital dynamics from Right Ascension.If you all would excuse me while I comment on some loose ends. The arithmetical progression of 24 hour days forms the basis of the calendar system hence the additional 24 hour rotational cycle of Feb 29th to square away the nearest proportion to a full 24 hour rotation matching an orbital circuit calculated at 365 1/4 rotations per circuit,in this case, 1461 rotations to 4 orbital circuits.This is what makes Ra/Dec homocentric rather than geocentric as the equatorial coordinate system using Ra/Dec maintains a steady progression of 24 hour days and rotations with the number of returns of a circumpolar star match the number of rotations as days and dates within the calendar system,people may fool themselves that there is a 3 minute 56 second divergence to 24 hours but this is mere trivia as all it takes is the ability to count. At one time I could say it amounted to people not doing their jobs but presently I have taken a different view and really unfortunately it would come down to criminal incompetence,it has to be considering the braking mechanism for the number of rotations in an orbital circuit of within context of the calendar system relies solely on cause and effect,in this case ,24 hours of rotation for each corresponding daylight/darkness cycle. The bottom to all this was reached quite some time ago and readers,indifferent or not,now wake up to astronomy as it should be practiced and specifically in this thread where researchers are really discussing homocentric ideologies rather than geocentric or to put it in another way - only an astronomer would know the difference. |
#16
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Converting RA/Dec to earth centered coordinates? (Correction)
On Mon, 02 May 2011 18:48:38 -0700, "W. eWatson"
wrote: On 5/2/2011 2:28 PM, Steve Willner wrote: In , "W. writes: My xy plane is in the plane of the equator, and its projection into the sky represents the celestial equator. Declination is measured +/- from the celestial equator to each pole along great circle lines that pass through each pole. Somewhere on the celestial equator is point from where RA is measured. To go from RA/Dec to an x,y,z unit vector is just simple trignometry: x = cos(dec)*cos(RA) y = cos(dec)*sin(RA) z = sin (dec) Make sure to convert RA/dec to degrees or radians (whatever units your calculator or program uses). It's easy to forget to multiply hours by 15 to get degrees. The zero point of RA is the place where the ecliptic and celestial equator intersect with the equinox heading north. Both this zero point and the location of the celestial poles changes with respect to the stars because of precession. If you want a _current_ x,y,z unit vector, you need to start from current RA/Dec coordinates rather than coordinates at a standard "ecliptic and equinox" (B1950 or J2000). The Meeus book will tell you how to do that calculation. Ah, the obliquity of the ecliptic (e) is what I need. Don't see why you need that. Did you mean ecliptic coordinates rather than celestial? Whoops, I posed the question backwards. I have the x,y,z coordinates of a vector and I want to convert them to ra/dec. In a unit sphere I think of z as pointing through the north pole, x pointing south through 1,0,0, and y pointing east through 0,1,0. In my case, precession does not enter into matters. I'm constructing a simulation that is mostly grounded in az/el and lat/lng. I wrote a program that produces the path of a fake meteor moving in a straight line. Time is not yet useful as a consideration yet. The direction of the line points to the radiant point in the sky. Meteors lie on a great circle, hence pass their plane passes through the earth's center (spherical earth). My program has not yet needed ra/dec, which is usually the measure of the radiant point in the sky and is given in ra/dec. However,I have the data from a similar program, and they provide the radiant as ra/dec. internally, my program seems sound when I sort of run it backwards. I get agreeable results. I want to see if the independent source and I agree. See if this explanation regarding nomenclature will help clarify things and perhaps bring an end to the random and inexplicable outbursts of vituperation. You have written a program that simply calculates the path of a meteor in XYZ coordinates whose origin is in the equatorial plane. From the XYZ coordinates you want to calculate the pitch and yaw or elevation and azimuth as measured on an equatorial mount that would point at the meteor. You apparently raised the hackles of purists by using the terms right ascension and declination which have specific astronomical meaning and are measured from the point of Aries if I recall correctly, and therefore has no place in your problem. I think you will find that the equations I gave you will give you the correct result. John Polasek |
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