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algorithms related to calculating equinoxes and solstices
Greetings all,
In Chapter.26 of Jean Meeus's Astronomical Algorithms, he introduced a way to calculate the JDE of the equinoxes and solstices of a given year. And we all know the apparent longitude of the Sun corresponding to these calculated JDEs would be 0, 90, 180 and 270 degrees, respectively. My question is how can I calculate the JDEs corresponding to other apparent longitudes, say, 15, 30, 45, 60 degrees, etc. Any idea would be helpful, thanks in advance. Cheers, Difei |
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algorithms related to calculating equinoxes and solstices
On Tue, 19 Apr 2011 22:32:53 -0700 (PDT), Difei
wrote: Greetings all, In Chapter.26 of Jean Meeus's Astronomical Algorithms, he introduced a way to calculate the JDE of the equinoxes and solstices of a given year. And we all know the apparent longitude of the Sun corresponding to these calculated JDEs would be 0, 90, 180 and 270 degrees, respectively. My question is how can I calculate the JDEs corresponding to other apparent longitudes, say, 15, 30, 45, 60 degrees, etc. Any idea would be helpful, thanks in advance. Cheers, Difei Meeus describes in that book how to compute the Sun's longitude åt a given date and time. I would apply either the secant method or a Newton-Rhapson iteration to that to fond the diverse (date+time of a given longitude). If you're unfamiliar with any of these words, look it up in Wikipedia. |
#3
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algorithms related to calculating equinoxes and solstices
On Apr 20, 7:32*am, Difei wrote:
Greetings all, In Chapter.26 of Jean Meeus's Astronomical Algorithms, he introduced a way to calculate the JDE of the equinoxes and solstices of a given year. And we all know the apparent longitude of the Sun corresponding to these calculated JDEs would be 0, 90, 180 and 270 degrees, respectively. My question is how can I calculate the JDEs corresponding to other apparent longitudes, say, 15, 30, 45, 60 degrees, etc. Any idea would be helpful, thanks in advance. Cheers, Difei The title of the thread should be 'how to use the calendar based Ra/ Dec system' which predicts rather than calculates different celestial events from solstices to solar eclipses ect. Solstices and equinoxes are orbital events and although it is fine for the man on the street to talk in terms of Spring equinox,summer solstice and things like that,in astronomical terms these things disappear and the events are demarcated as the December solstice or the September equinox as these relate to specific orbital characteristics as the planet turns through 360 degrees to the central Sun in generating a single orbital daylight/darkness cycle. You want to be a mechanical monkey then good for you,the system you are using is based on a proportion of 1461 rotations for 4 orbital circuits but more importantly,it is grouped in batches of 365 and 366 rotations rather than the raw rotational orbital proportion of 365 1/4 rotations to 1 orbital cycle. In case you are wondering,what you are asking is a step below geocentricity which is homocentricity,you will know this as the axis of a telescope tracking a circumpolar star,which unfortunate people imagine substitutes for constant and steady rotation,creates its own individual axis of rotation and far removed from the North/South Polar coordinates which reader here believe they are witnessing.You need to be an astronomer to know the differences,some of these things are intricate and empiricists often exploit these intricacies for obfuscation purposes and therein is the tragedy,the timekeeping system we inherited is incredible,even the convenience of the Ra/Dec system has its purposes but there are limits to what that system represents. |
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algorithms related to calculating equinoxes and solstices
On Apr 19, 10:32*pm, Difei wrote:
Greetings all, My question is how can I calculate the JDEs corresponding to other apparent longitudes, say, 15, 30, 45, 60 degrees, etc. Any idea would be helpful, thanks in advance. Difei, It is *very* difficult to cherrypick your way through Meuss to find specific 'ad hoc' calculations that you may need for any observations, projects etc. Some things you may be able to get from JPL Horizons http://ssd.jpl.nasa.gov/horizons.cgi or from the Harvard MPL. http://www.minorplanetcenter.net/iau/MPEph/MPEph.html I would suggest that you byte the bullet and reconcile yourself to the fact that you are going to have to do your very own Excel spreadsheet. This is because Meeus is constantly referring you back to earlier chapters and this is a pain "ol wazoo". But Meeus is addictive and once you start getting the terms in place you will want to keep after it. In spite of the fact that 'Astronomical Algorithms' comes from the Golden Age of desktop computing (Basic, Quick Basic etc) it lends itself to spreadsheet calculation readily. If you don't have Excel you can get it in "Open Office" for free. If you don't know how to operate in Excel you can learn it by doing the calculations in "Astronomical Algorithms". ( I did.) So do you have Excel? Ben |
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algorithms related to calculating equinoxes and solstices
On Apr 20, 12:21*pm, Ben wrote:
On Apr 19, 10:32*pm, Difei wrote: Greetings all, PS Paul Schlyter mentions an iteration method (with which I am not familiar) and iteration is the key to performing many these calculations from Meuss. *You can bypass many of the formulas he gives by simply iterating conjugate (+/-) terms and get more accurate results!* This is especially true of rising/setting/transit calculations or in dealing with planetary distances at oppositions. The calculations dealing with Kepler's formula require several iterations which are easily accomplished on Excel by extending the iterations with a mouse click and drag. Do a few cell entries *every day* and in a couple of months you will have most of Astronomical Algorithms in place and functioning. |
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algorithms related to calculating equinoxes and solstices
On Apr 20, 9:21*pm, Ben wrote:
On Apr 19, 10:32*pm, Difei wrote: Greetings all, My question is how can I calculate the JDEs corresponding to other apparent longitudes, say, 15, 30, 45, 60 degrees, etc. Any idea would be helpful, thanks in advance. Difei, * * It is *very* difficult to cherrypick your way through Meuss to find specific 'ad hoc' calculations that you may need for any observations, *projects etc. *Some things you may be able to get from JPL Horizonshttp://ssd.jpl.nasa.gov/horizons.cgi or from the Harvard MPL.http://www.minorplanetcenter.net/iau/MPEph/MPEph.html I would suggest that you byte the bullet and reconcile yourself to the fact that you are going to have to do your very own Excel spreadsheet. *This is because Meeus is constantly referring you back to earlier chapters and this is a pain "ol wazoo". *But Meeus is addictive and once you start getting the terms in place you will want to keep after it. *In spite of the fact that 'Astronomical Algorithms' comes from the Golden Age of desktop computing (Basic, Quick Basic etc) it lends itself to spreadsheet calculation readily. If you don't have Excel you can get it in "Open Office" for free. *If you don't know how to operate in Excel you can learn it by doing the calculations in "Astronomical Algorithms". ( I did.) So do you have Excel? Ben Here you go Ben,here is something which brings you into the realm of interpretation rather than impressing yourselves - http://www.jpl.nasa.gov/education/index.cfm?page=123 As the moon orbits the Earth while having no intrinsic rotation,you can see the phases as sometimes the Earth intervenes between the orbiting moon and the Sun and sometimes the moon is between the Earth and the Sun(New Moon). Don't know why it is happening in not having another living human being who can simply affirm basic astronomical facts and the moon orbiting the Earth without latitudinal variations in rotation speed is one of them even after the engineering feat of landing men on the moon hence the inability to intepret lunar motion cancels out any achievement in send people there. |
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algorithms related to calculating equinoxes and solstices
On Apr 20, 9:00*pm, oriel36 wrote:
On Apr 20, 9:21*pm, Ben wrote: Don't know why it is happening in not having another living human being who can simply affirm basic astronomical facts and the moon orbiting the Earth without latitudinal variations in rotation speed is one of them even after the engineering feat of landing men on the moon hence the inability to intepret lunar motion cancels out any achievement in send people there. Gerald, once again your text is reading like it came from a bot. I mean look at that last paragraph. It is a trophy run-on sentence. I know you can write better than that because I've read better than that from you. Are you getting "sloshed" again? |
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algorithms related to calculating equinoxes and solstices
On Apr 20, 10:00*pm, oriel36 wrote:
you can see the phases as sometimes the Earth intervenes between the orbiting moon and the Sun and sometimes the moon is between the Earth and the Sun(New Moon). That would be eclipses. Phases come from the Moon intervening between the surface of the Moon and the Sun. John Savard |
#9
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algorithms related to calculating equinoxes and solstices
On Apr 21, 7:30*am, Ben wrote:
On Apr 20, 9:00*pm, oriel36 wrote: On Apr 20, 9:21*pm, Ben wrote: Don't know why it is happening in not having another living human being who can simply affirm basic astronomical facts and the moon orbiting the Earth without latitudinal variations in rotation speed is one of them even after the engineering feat of landing men on the moon hence the inability to intepret lunar motion cancels out any achievement in send people there. Gerald, once again your text is reading like it came from a bot. Don't worry child,I am not going to ask you if the moon rotates because I know you believe it does hence personal insults are meaningless when you can't interpret something so fundamental to human understanding like the fact that the moon has an orbital motion of the Earth but no rotation,if you have any difficulties then the NASA website should explain to you using a simple analogy how lunar dynamics using the Earth and the Sun creates the observed phases. *I mean look at that last paragraph. *It is a trophy run-on sentence. I know you can write better than that because I've read better than that from you. *Are you getting "sloshed" again? You get the luxury of saying whatever you want as I rarely ask a reader a question as I asked you such as the proportion of rotations for 4 orbital circuits (1461 rotations) in order to establish where you stand ,you didn't affirm or reject the 1461 rotations which stretch across the calendar system so you become just another nuisance in a forum that has known many. What it must take to create an imbalance between the amount of rotations and the equivalent amount of day/night cycles,as this is where your algorithms lead to in following stellar circumpolar reasoning of 366 1/4 rotations must be a painful experience whereas the lack of affirmation of 1461 rotations and day/night cycles is merely temporarily dismaying so 'slosh' all you like,if you can manage to believe what you do,I wouldn't care what you had to say. |
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algorithms related to calculating equinoxes and solstices
On Apr 21, 8:29*am, oriel36 wrote:
On Apr 21, 7:30*am, Ben wrote: On Apr 20, 9:00*pm, oriel36 wrote: Gerald, once again your text is reading like it came from a bot. Don't worry child,I am not going to ask you if the moon rotates because I know you believe it does hence personal insults are meaningless when you can't interpret something so fundamental to human understanding like the fact that the moon has an orbital motion of the Earth but no rotation,if you have any difficulties then the NASA website should explain to you using a simple analogy how lunar dynamics using the Earth and the Sun creates the observed phases. Happy are they who can hear their detractions and set them to mending. Shakespeare mean look at that last paragraph. *It is a trophy run-on sentence. |
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