Sun position code

[Chris]

Hello,

I'm hoping someone here can save me a bunch of time: I need to compute the obliquity of the ecliptic, mean longitude of the Sun, and mean anomaly of the Sun at some epoch. It does not need to be very accurate. I would really prefer to use existing code for this and not try to cobble something together myself, as I am not an astronomer. I've seen sunpos.jl in AstroLib.jl, but it's not usable in its current form. Does this exist somewhere?

Thanks in advance,

Chris

[nirinA]

have a look at:

https://github.com/JuliaAstro/ERFA.jl

there are eraObl06 and eraObl80 for the obliquity of the ecliptic,
and eraFaxx03 for mean longitude and anomaly of orbiting bodies.

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nirinA

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[Chris]

Thanks. I knew about ERFA.jl, I should've checked that a little more thoroughly. I see eraFalp03, which returns mean anomaly of the Sun (according to the SOFA doc, at least), but I can't find a function that returns mean longitude.

> <mailto:julia-astro+unsub...@googlegroups.com>.

[nirinA]

eraFaom03 - eraFad03 ?

note that the fundamental arguments relative to the planets
are their mean heliocentric ecliptic longitudes.

--
nirinA

Chris wrote:
> Thanks. I knew about ERFA.jl, I should've checked that a little more
> thoroughly. I see eraFalp03, which returns mean anomaly of the Sun
> (according to the SOFA doc, at least

> <http://www.iausofa.org/2008_0301/sofa/sofa_lib.lis>), but I can't

[Chris]

Hmm, "elongation" is a new term to me. Thanks for your help.

[Mosè Giordano]

Hi Chris,

2016-05-16 18:13:32 GMT+2 Chris:

Hello,

I'm hoping someone here can save me a bunch of time: I need to compute the obliquity of the ecliptic, mean longitude of the Sun, and mean anomaly of the Sun at some epoch. It does not need to be very accurate. I would really prefer to use existing code for this and not try to cobble something together myself, as I am not an astronomer. I've seen sunpos.jl in AstroLib.jl, but it's not usable in its current form. Does this exist somewhere?

Why do you say that sunpos function in AstroLib.jl is not usable?  It can't be used alone because it relies on other functions part of the library, but the whole library is self-sufficient.  If you mean that there isn't a tagged version providing that function, I can release a new one.

Bye,
Mosè

[Chris]

Admittedly I did not spend much time trying to get it working, but I checked out master and included sunpos.jl, but I still got an error. I did not pursue it further.

[Mosè Giordano]

2016-05-18 17:25 GMT+02:00 Chris:

Admittedly I did not spend much time trying to get it working, but I checked out master and included sunpos.jl, but I still got an error. I did not pursue it further.

So you only issued

include("/path/to/sunpos.jl")

?  If so, this is definitely a problem, AstroLib.jl is intended to be used as a package (like any other Julia package I know), not a collection of independent (and sometimes inconsistent) functions like IDL AstroLib.  AstroLib.jl's functions are in different files just for convenience.

Instead, if you loaded the whole package and got an error it would be great to know which error ;-)

Bye,
Mosè

[Chris]

Well, no, I did some combination of using AstroLib and the include statement, one problem is that sunpos.jl is not included when the module is loaded. I can tell you that trying it again now (`using AstroLib`, that is), I get the following error:

iERROR: LoadError: LoadError: SystemError: opening file C:\Users\cbinz\.julia\v0.4\AstroLib\src\..\deps\NP.xy: No such file or directory

 in open at iostream.jl:90

 in open at iostream.jl:112

 in readdlm_auto at datafmt.jl:45

 in readdlm at datafmt.jl:39

 in readdlm at datafmt.jl:36

 in anonymous at C:\Users\cbinz\.julia\v0.4\AstroLib\src\common.jl:13

 in include at boot.jl:261

 in include_from_node1 at loading.jl:320

 in include at boot.jl:261

 in include_from_node1 at loading.jl:320

 in require at loading.jl:259

while loading C:\Users\cbinz\.julia\v0.4\AstroLib\src\common.jl, in expression starting on line 11

while loading C:\Users\cbinz\.julia\v0.4\AstroLib\src\AstroLib.jl, in expression starting on line 15

[Chris]

I see now that sunpos.jl is included via utils.jl, so I was wrong about that.

[Mosè Giordano]

2016-05-18 18:50 GMT+02:00 Chris:

Well, no, I did some combination of using AstroLib and the include statement, one problem is that sunpos.jl is not included when the module is loaded. I can tell you that trying it again now (`using AstroLib`, that is), I get the following error:

iERROR: LoadError: LoadError: SystemError: opening file C:\Users\cbinz\.julia\v0.4\AstroLib\src\..\deps\NP.xy: No such file or directory

 in open at iostream.jl:90

 in open at iostream.jl:112

 in readdlm_auto at datafmt.jl:45

 in readdlm at datafmt.jl:39

 in readdlm at datafmt.jl:36

 in anonymous at C:\Users\cbinz\.julia\v0.4\AstroLib\src\common.jl:13

 in include at boot.jl:261

 in include_from_node1 at loading.jl:320

 in include at boot.jl:261

 in include_from_node1 at loading.jl:320

 in require at loading.jl:259

while loading C:\Users\cbinz\.julia\v0.4\AstroLib\src\common.jl, in expression starting on line 11

while loading C:\Users\cbinz\.julia\v0.4\AstroLib\src\AstroLib.jl, in expression starting on line 15

It seems that the build script hadn't been run (how did you install the package?  This is done automatically when installing the package with Pkg.add("AstroLib")), so the file NP.xy wasn't there.  But it is used only in a function, it isn't fundamental, I'll had a check about existence of that file: if it's missing there will be not error, just a warning.  Thanks for pointing this out!  Anyway, you can run the build script manually with

Pkg.build("AstroLib")

and then everything should work just fine.

Bye,
Mosè

[Chris]

I think I see what happened: I installed v0.0.5 with the usual `Pkg.add("AstroLib")``, but that version does not include `sunpos`. So I checked out `master`, but did not re-build the package after doing so. Checking out `master` and manually building works. A new tagged version would be useful. Thanks for your help.

[Mosè Giordano]

Hi Chris,

2016-05-18 20:20 GMT+02:00 Chris:

A new tagged version would be useful.

 
AstroLib 0.0.6 is now out there ;-)

Bye,
Mosè