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algorithms related to calculating equinoxes and solstices



 
 
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  #1  
Old April 20th 11, 06:32 AM posted to sci.astro.amateur
Difei
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Posts: 2
Default 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
  #2  
Old April 20th 11, 11:48 AM posted to sci.astro.amateur
Paul Schlyter[_3_]
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Posts: 1,344
Default 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  
Old April 20th 11, 06:24 PM posted to sci.astro.amateur
oriel36[_2_]
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Posts: 8,478
Default 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.







  #4  
Old April 20th 11, 08:21 PM posted to sci.astro.amateur
Ben[_2_]
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Posts: 181
Default 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






  #5  
Old April 20th 11, 09:09 PM posted to sci.astro.amateur
Ben[_2_]
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Posts: 181
Default 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.
  #6  
Old April 21st 11, 05:00 AM posted to sci.astro.amateur
oriel36[_2_]
external usenet poster
 
Posts: 8,478
Default 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.



  #7  
Old April 21st 11, 06:30 AM posted to sci.astro.amateur
Ben[_2_]
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Posts: 181
Default 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?
  #8  
Old April 21st 11, 08:28 AM posted to sci.astro.amateur
Quadibloc
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Posts: 7,018
Default 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  
Old April 21st 11, 04:29 PM posted to sci.astro.amateur
oriel36[_2_]
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Posts: 8,478
Default 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.











  #10  
Old April 21st 11, 04:44 PM posted to sci.astro.amateur
Ben[_2_]
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Posts: 181
Default 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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