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#11
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Celestial sphere image?
Skywise wrote:
Dave Typinski wrote in news Something to do with the Earth's axis tilting. Seems we're doing the same thing. ;-) Well then. Seems I'll have ot finish up my work and then we can compare notes. Sounds like a plan. It's not like I'm doing this for hire. The down side is that I've 74,880 frames to render--and each one takes about 35 seconds on this dual core Opteron box. That's about a CPU-month of rendering out of Blender. At what resolution? 640x480. The reason it was taking so long is that I was doing a motion blur on each frame with 16 oversamples per frame. I decided I can cut that down to 5 oversamples and reduce the background stars resolution, which got it down to around 7.5 seconds per frame. My goal is HDTV 1920x1080, which take about 30 or so seconds per frame, but I do test runs at much lower resolutions so it only takes me a few minutes to check a scene for results. I'm shooting for the same final resolution, but then that'll get cut down for web presentation. What 3D app are you using? And what render engine? I've been tempted to try rendering via YafRay instead of Blender's internal engine. Haven't got the gumption up yet to do it, mostly because ray tracing, while producing incomparably superb results, takes approximately forever to render an image. Blender is a nice tool, but it's rather quirky. It doesn't always do what it's supposed to do, let alone what you want it to do. I've come close to starting over with a professional tool like Cinema4D--but the allure (i.e., price) of open source keeps me using Blender. But, that's on a Core2 duo 3Ghz. I also have a quad and when I'm ready for the final render I'll be doing a network render job. If you want long rendering times, do a full raytrace with caustics and index of refraction through complex glass objects. snooooooze No thanks. I've avoided ray traced materials in this project for that very reason. I read an article about the rendering involved in making the movie "Iron Man"--it claimed that the scenes with lots (3,000+) of animated elements took eight hours per frame to render--although they didn't say whether that was on a render farm or how many nodes there were in the network. I heard back from the man who made those star map images to which you linked. Here's the process to create a UV-mappable celestial sphere, according to him: Take screenshots from your favorite astronomy software by positioning the virtual telescope all around the sky. He used images with an angular view of around 42° or so, but there's no reason one couldn't go smaller or larger depending on the final output resolution needed. Assume those screen caps are normal rectilinear projections. They may not be, but close enough. Use stitching software like PTGui (payware) or hugin (open source) to internally wrap the separate images onto a spherical surface and produce an equirectangular projection of that sphere as the output. That output is then suitable for UV mapping in 3D modeling software. -- Dave |
#12
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Celestial sphere image?
On May 11, 9:34*am, oriel36 wrote:
How intelligent does a person need to be to see that extending the Earth's spherical geometry *into the celestial arena *via a calendar driven Ra/Dec convention and without any qualifiers whatsoever will produce a celestial sphere geometry ?. It is true that when we talk about directions from the Earth, these directions form a "celestial sphere". But this does not mean that using such a construct implies we must believe in a literal firmament, and deny that the distant galaxies are much farther away than the near stars. The possible directions away from the Earth correspond to the points on a sphere; such a correspondence does not require an actual sphere to exist. Whatever drives people to believe that daily rotation to a stationary celestial sphere does not retain the architecture of the apparent motion about Polaris I do not know, but using a celestial sphere to justify daily rotation has consequences which close to being a dishonorable to human intelligence as it is possible to get - You may have your rhetoric, but this is not seen. In order to retain daily rotation to a rotating celestial sphere as the reference for everything in the Universe and subsequently rotational orientation to Polaris,they had to introduce a wandering analemma Sun to blur the original distinction between daily rotation and its true reference - natural noon. Natural noon, as you point out, is unequal in the duration from one natural noon to the next because of the Equation of Time. The Earth's orbital motion is the source of that inequality, as you yourself stated in a recent post: (begin quote) The natural noon benchmark which creates the seamless transition from one 24 hour day to the next contains the natural inequalities which arising from the orbital motion of the Earth. (end quote) If we try to refer the unequal natural noon to a 24-hour uniform rotation, then the result would be the cosmology of Tycho Brahe, *with* a "wandering analemma Sun"; absent orbital motion of the Earth around the Sun, the Sun would have to wiggle around in an actual motion corresponding to the shape of the analemma. But the Sun does not do this - it remains at the center, and the Earth moves around the Sun in an orbit. If we consider the Earth'a axial rotation _from the same perspective_ as the Earth's orbit, we see the uniform axial rotation which when combined with the Earth's orbital motion yields the complicated compound motion that is natural noon. This is simple, clear, and straightforward. It does not insult human intelligence; it reflects the thinking of Copernicus and Kepler. Only your own confusion leads you to think otherwise. Call it what you will,a nightmare or a crisis, Ah, yes, the old headline trick: Isaac Newton: threat or menace? John Savard |
#13
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Celestial sphere image?
On May 12, 3:58*am, palsing wrote:
On May 10, 10:50*pm, oriel36 wrote: How is it possible that in the 21st century that a person can knowingly and without the expectation of any objection can discuss celestial sphere things as actual instead of the horror that it is ?.I am sure some know by now ******************* And I am just as sure that you are just about the only person on the planet who thinks this way. It must be lonely at the top... very lonely... Tell me how long does it take Polaris to return to your meridian and I will tell you that imposing the Earth's geometry into the celestial arena is what people are doing by following Flamsteed ,they do not know they are doing it and seriously do not believe they are retaining the astrological architecture but that is what you get when you create a solar vs sidereal fiction which has no basis in principle never mind in observation and then justifying it using daily rotation and orbital motion. If participants wants to the quasi- holographic image of what they believe by linking the daily rotation of the Earth directly to a stationary celestial sphere or a rotating celestial sphere to a stationary Earth in 23 hours 56 minutes 04 seconds then here it is - http://www.opencourse.info/astronomy...phere_anim.gif With the first sign that holographic imaging will play an enormous role in translating observations through powerful imaging,I am still stuck here with those who have enclose the universe in a celestial sphere bubble by projecting the Earth's spherical geometry into space with matching concepts !. I wish people would give up the pretense that it is not a crisis,deal with the matter and move on to actual productive astronomy ,instead,I have to deal with people,who at best, sound like they drink cups of vinegar so sullen are the responses. |
#14
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Celestial sphere image?
In sci.astro.amateur message
, Sun, 10 May 2009 20:57:16, Dave Typinski posted: As I've mentioned before, I'm making some animations to show Earth's rotation, orbit, precession, and all that other fun rotational stuff. Blame it on Oriel. As you know how to do that sort of thing ... There are plenty of maps of the Celestial Sphere showing the positions of stars & nebulae, and sometimes of other things real and artificial - sun, moon, planets, the ecliptic, lines of celestial lat & long, constellation borders, constellation figures. But I don't recall one primarily showing orbital and rotational axes projected on to the Sphere. Those for the major Solar System objects must be well enough known, as is that for at least our Galaxy. ISTM that such a map would be of interest; it would have also some indication of lat and long, the ecliptic, and perhaps the shapes of three of four zodiacal constellation, and of UMa/UMi, and of whatever seems best for the South Pole (the Cross & the Clouds?), for indicating orientation. There would be room to indicate the paths of precession, too. -- (c) John Stockton, nr London, UK. Turnpike v6.05. Web URL:http://www.merlyn.demon.co.uk/ - w. FAQish topics, links, acronyms PAS EXE etc : URL:http://www.merlyn.demon.co.uk/programs/ - see 00index.htm Dates - miscdate.htm moredate.htm js-dates.htm pas-time.htm critdate.htm etc. |
#15
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Celestial sphere image?
On May 12, 6:25*am, oriel36 wrote:
Tell me how long does it take Polaris to return to your meridian The answer to your question as you have asked it is, of course, that it never leaves the meridian. Actually, since Polaris is some slight distance away from the north celestial pole, the "real" answer is the same 23 hours 56 minutes and 4 seconds as any other star, though, which I must note or some people here will correct me. If participants wants to the quasi- holographic image of what they believe by linking the daily rotation of the Earth directly *to a stationary celestial sphere or a rotating celestial sphere to a stationary Earth in 23 hours 56 minutes 04 seconds then here it is - The URL you provide showed an animated .GIF which illustrates the Ptolemaic view of the Universe, with the stars on a sphere which revolves around the Earth. That certainly is wrong, and it would be a bad thing to believe that. The stars are enormously far away, so of course it would be silly to have them move around the Earth once a day. But it would also be silly to have them move around the Earth *once a year*. If we let the distant stars remain fixed, then this means we must accept that the actual rotational period of the Earth is what is referenced to them. Thus, it is the 23 hour, 56 minute, and 4 second view that lets the stars remain unmoving. instead,I have to deal with people,who at best, sound like they drink cups of vinegar so sullen are the responses. I understand you are only trying to help bring clarity and understanding, but you are mistaken, so you cannot achieve that goal until you stop and examine your own mistakes. John Savard |
#16
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Celestial sphere image?
Quadibloc wrote:
If we let the distant stars remain fixed, then this means we must accept that the actual rotational period of the Earth is what is referenced to them. Thus, it is the 23 hour, 56 minute, and 4 second view that lets the stars remain unmoving. A proof closer to home is to examine the relationship of satellite orbit altitude and orbit period. Geostationary satellites live at an orbit radius of 42,165 km, plus or minus a couple kilometers. Given Earth's mass and that orbit radius and Newton's laws of motion and gravitation, they orbit in one sidereal day plus or minus a few seconds. To do a full orbit in one solar day, they'd have to be either a) higher by about 80 km or b) the Earth would have to be lighter by about 3x10^19 metric tons. Since they aren't higher and Earth isn't lighter, they don't orbit in one solar day, but in a sidereal day. Since they're geostationary, the Earth itself must complete one rotatation in one sidereal day, not in one solar day. QED. Rotation is only absolute when referenced to the fixed stars. Rotation referenced to other frames is valid and useful, but it's relative rotation, not absolute. A nifty resource: http://www.1728.com/kepler3a.htm -- Dave |
#17
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Celestial sphere image?
Dr J R Stockton wrote:
In sci.astro.amateur message , Sun, 10 May 2009 20:57:16, Dave Typinski posted: As I've mentioned before, I'm making some animations to show Earth's rotation, orbit, precession, and all that other fun rotational stuff. Blame it on Oriel. As you know how to do that sort of thing ... There are plenty of maps of the Celestial Sphere showing the positions of stars & nebulae, and sometimes of other things real and artificial - sun, moon, planets, the ecliptic, lines of celestial lat & long, constellation borders, constellation figures. But I don't recall one primarily showing orbital and rotational axes projected on to the Sphere. Those for the major Solar System objects must be well enough known, as is that for at least our Galaxy. True enough. One could embellish the sphere with all sorts of celestial equators and rotational axes. Good project for the future; thanks for the idea. ISTM that such a map would be of interest; it would have also some indication of lat and long, the ecliptic, and perhaps the shapes of three of four zodiacal constellation, and of UMa/UMi, and of whatever seems best for the South Pole (the Cross & the Clouds?), for indicating orientation. There would be room to indicate the paths of precession, too. Yep. All sorts of nifty visualizations can be included. -- Dave |
#18
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Celestial sphere image?
Dave Typinski wrote in
: I'm shooting for the same final resolution, but then that'll get cut down for web presentation. My plan as well. In fact, I recently purchased some video editing software to help me in such endeavors. If you want long rendering times, do a full raytrace with caustics and index of refraction through complex glass objects. snooooooze No thanks. I've avoided ray traced materials in this project for that very reason. I use POVRay as well and I have a project I've been wanting to render...errr...ray-trace for quite some time. I made a simple scene of various sized diamonds sitting on a mirrored turntable. I have done single frame renders and they took forever it seemed, but look really good. I want to do a full 360 degree rotation animation, but I think I calculated that my quad core system would take at least a month to render it, and that's running 24/7 flat out. I heard back from the man who made those star map images to which you linked. Here's the process to create a UV-mappable celestial sphere, according to him: Sniopola Use stitching software like PTGui (payware) or hugin (open source) to internally wrap the separate images onto a spherical surface and produce an equirectangular projection of that sphere as the output. Sweet. Thanks for the info. I have hugin already for my digital panorama photography. Never even occured to me to use it for this. That actually opens up a LOT of possibilities. Now if only I didn't work 50+ hours a week.... Brian -- http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html Sed quis custodiet ipsos Custodes? |
#19
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Celestial sphere image?
On May 12, 11:27*pm, Dave Typinski wrote:
Quadibloc wrote: If we let the distant stars remain fixed, then this means we must accept that the actual rotational period of the Earth is what is referenced to them. Thus, it is the 23 hour, 56 minute, and 4 second view that lets the stars remain unmoving. A proof closer to home is to examine the relationship of satellite orbit altitude and orbit period. * The 'sidereal time vs solar time' fiction which uses the motions of the Earth to justify itself is easily disproved,the independent daily rotation of the Earth through 360 degrees in 23 hours 56 minutes 04 seconds is the astronomical equivalent of Piltdown man,even in principle,the value requires two additional qualifiers and cannot be proposed as an independent fact,,the qualifiers being that a star returns to a meridian in 23 hours 56 minutes 4 sec based on the 24 hour average day within the equable 365/366 day calendar system. Since they aren't higher and Earth isn't lighter, they don't orbit in one solar day, but in a sidereal day. *Since they're geostationary, the Earth itself must complete one rotatation in one sidereal day, not in one solar day. *QED. The Earth must not do anything,that is just the sound of numbskulls trying to force a round peg into a square hole where the bridge between the fictional sidereal vs solar day is expressed in 3 minutes 56 second orbital terms - http://en.wikipedia.org/wiki/Sidereal_day In comparative terms,this is astronomical 'ground zero',the first attempt to take a known and stable astronomical principle which rely on raw observations of the natural noon inequality and fudge the observations to fit the conclusions.It is happening today with conclusions based on carbon dioxide and global warming but fundamentally it all began with Flamsteed and his ill-considered conclusion by using the return of the star Sirius to his meridian as a gauge to judge daily and orbital motions - "... our clocks kept so good a correspondence with the Heavens that I doubt it not but they would prove the revolutions of the Earth to be isochronical..." John Flamsteed 1677 Rotation is only absolute when referenced to the fixed stars. What you are trying to say is that the rotation of the Earth through 360 degrees can be expressed as an independent fact aside from orbital motion hence these insane individual leap second corrections linked to variations in daily rotation.What you do not know is that ,inherent in the conclusion of Flamsteed which reflects your statement, is the astrological architecture which projects the Earth's spherical geometry into the celestial arena as a structural fact - http://www.opencourse.info/astronomy...phere_anim.gif Your absolute rotation and your absolute universe looks like that,if you can't figure out the reasoning why the astrological architecture infects all reasoning ahead of it and especially the further distortions introduced by Newton,then you will hardly understand the genuine consequences which surface in the inability to deal with climate issues properly. Rotation referenced to other frames is valid and useful, but it's relative rotation, not absolute. A nifty resource:http://www.1728.com/kepler3a.htm -- Dave This is not an exercise in convincing people they are wrong,this is a call for astronomers who can provide the platform for stable conceptual approaches to astronomy and the effects of planetary dynamics on terrestrial disciplines such as climate and geology.It is clear that the majority cannot grasp the cross currents of arguments,some historical,some ideological but mostly technical which have contributed to the current crisis however there are always people,even those who were originally hostile,who have the intelligence and the courage to deal with the matter effectively . You can,in the 21st century, openly reason that the Earth rotates through 360 degrees in 23 hours 56 minutes 04 without fear of objection and that is pretty shocking.I can tell those who may wish to return to the restore point of the natural noon inequality that nobody is required to know the exact technical and historical details of how the 24 hour day emerged through the variations in length of time it took the Sun to return to a meridian,only that the convenience of transferring the average 24 hour day to 'constant' daily rotation is just a quirk and advantage of the original system hence there is no external celestial reference for daily rotation as an independent motion. |
#20
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Celestial sphere image?
On May 13, 4:00*am, oriel36 wrote:
the qualifiers being that a star returns to a meridian in 23 hours 56 minutes 4 sec based on the 24 hour average day within the equable 365/366 day calendar system. How is this a problem? The 24 hour average day is a consequence of us wanting our clocks to register noon when the Sun is in fact high in the sky. So we choose the size of our uniform unit of time to correspond to that. That the Earth's rotation has a certain odd length when measured by that clock - and the Earth's revolution around the Sun has another odd length when measured by that clock - is to be expected. It seems that you're trying to say that since the hour, minute, and second are derived from natural noon, by averaging it, one can't then turn around and say that natural noon is derived from this time scale; that's going around in circles, or pulling yourself up by your own bootstraps. We don't look at it that way, and in fact, your objection is sufficiently unintelligible to us that without you spelling it out, it's hard to see what it even consists of. Uniform time, instead of being *derived* from natural noon, is fundamental, resting on the motions of pendulums or other devices from which a mechanical clock can be built. Only the size of the unit arose from comparisons with natural noon, and this for convenience in use for customary civil purposes. The Earth must not do anything,that is just the sound of numbskulls trying to force a round peg into a square hole Ah, yes; all this stuff about centrifugal force balancing gravity and being equal to velocity squared over the radius or angular velocity squared times the radius is just Newtonian empiricism. What you are trying to say is that the rotation of the Earth through 360 degrees can be expressed as an independent fact aside from orbital motion You've got it. And it works; Sirius still does return to the meridian at a uniform time by our clocks (except for variations which are very much smaller than those in the Equation of Time, which have their own explanations). What you do not know is that ,inherent in the conclusion of Flamsteed which reflects your statement, is the astrological architecture which projects the Earth's spherical geometry into the celestial arena as a structural fact *- Angles and directions exist without a spherical shell. that the convenience of transferring the average 24 hour day to 'constant' daily rotation is just a quirk and advantage of the original system hence there is no external celestial reference for daily rotation as an independent motion. Galileo discovered that the period of a pendulum does not change much as it swings less widely; thus, pendulums were particularly useful for making mechanical clocks. Using mechanical clocks, and rulers with a uniform standard of length, we found that we could derive simple rules for the behavior of moving objects. This meant using the mechanical clock as the standard, as the starting point; later, when it became possible to understand the motions of the heavenly bodies, they were explained in terms of a uniform time scale. Natural noon was not uniform. The return of a star did conform to the behavior of mechanical clocks - and so, since, until recently, the Earth's rotation was more uniform than our best mechanical clocks, it was the return of a star that was used to calibrate Ephemeris Time, the uniform time scale which gave rise to the size of a second in the atomic clock time scale (which does not quite fit the average length of the natural noon cycle at present, hence leap seconds). The motion which is uniform by the mechanical clock is the one that is simple, hence it is the appropriate one to regard as independent if we seek understanding of the causes of the motions of the heavenly bodies. You would lead us away from understanding, not towards it, if we followed your advice. John Savard |
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