Earth's position relative to heliocentric equatorial plane or helio ecliptic plane..

[Benjamin Brink]

Hi, 

How can one determine the relative orientation of the solar equator to a position at Earth's core for a given time?

This is for interpreting equatorial dynamics of images of the solar disk from Earth.

I understand the Sun is tilted (has Obliquity to ecliptic) of 7.25 degrees per http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html

I've tried a few queries at JPL Horizon's, but am not seeing the 7+ degree difference at any time in a year's worth of data. My queries are asking for something else. :-/

I wrote a Keplerian ephemeris using http://ssd.jpl.nasa.gov/?planet_pos  thinking that the orbits would be transformed to or from a heliocentric orientation (or poles or heliocentric equatorial plane) compared to Earth's plane of ecliptic. The instantaneous angle could then be calculated. However, results show it computes per Earth's J2000 ecliptic plane. 

If Kepler orbital parameters for the sun are available, it might still work.. the Sun's orbital parameters would be a tight, inclined orbit to the sol system barycenter.

AFAICT, this is a place to ask this question. If not, please suggest another.

Thank you.

[Benjamin Brink]

Franz and Harper's"Heliospheric coordinate systems" appears to also reference the Earth ecliptic orbital plane for the Heliocentric coordinate systems with references to "GEI J2000". Table 6 includes the Sun with same coordinate system.

Oh, hmm. Section 3.2.1. "Solar Pole and prime meridian" on page 4 provides some parameters that might work:

"Heliographic coordinate systems use the position of the solar rotation axis which is defined by its declination and the right ascension with respect to the celestial pole (GEIJ 2000 + Z)."

Now to decipher.. ;-)  

Thank you for your time.

-----

 ( M. Franz, D. Harper / Planetary and Space Science 50 (2002) 217–233 . 221 retrieved from http://jsoc.stanford.edu/doc/keywords/coordinates/Franz_Harper_2002.pdf )

[Benjamin Brink]

I'm having difficulty decoding the terminology in this Franz-Harper paper. 

What is GEI j2000? I know j2000, just not sure of the GEI.

In section 3.2.1, the paper states solar polar orientation is 

  Declination 63.87degrees; Right Ascension 286.13 degrees for GEI j2000. 

I'm unable to visualize the Sun's polar orientation as being 63.87 degrees from anything geocentric including if GEI = Geocentric Equatorial Inclination.  Is GEI  Galactic Ecliptic Inclination? ?

I don't think I've ever seen the solar equator vary by more than maybe 15 degrees even from space probes in heliocentric orbit (except Ulysses).

Can anyone recommend another resource?  Or provide another description of the relation of the solar polar orientation to Earth polar orientation? 

I'm just looking for the tilt of the Sun relative to Earth for a given time (this century).  Something that can be used to project a virtual heliocentric grid, such as shown in the lower right image at http://www.nso.edu/current_images.html

[Benjamin Brink]

Nevermind. Found answer.  GEIJ 2000 = Geocentric Earth Equatorial.

will work with that.

[Derek Lamb]

On Mar 13, 2016, at 11:12 PM, Benjamin Brink <xdc...@gmail.com> wrote:

Hi, 

How can one determine the relative orientation of the solar equator to a position at Earth's core for a given time?

Go to http://ssd.jpl.nasa.gov/horizons.cgi.  Select the "Observer" Ephemeris type, "Sun" as the target body, "Geocentric" for the observer location, and in Table Settings make sure you have at least #14 "Observer sub-lon & sub-lat" selected.  If you select the default time range, you'll get today + 30 days, and you'll see the observer sub longitude is about -7.16 deg and increasing, which is correct: Earth is south of the solar equator at the moment.

I've tried a few queries at JPL Horizon's, but am not seeing the 7+ degree difference at any time in a year's worth of data. My queries are asking for something else. :-/

You didn't say what was in your queries.  Without knowing that, it's hard to guess what you were doing incorrectly.

AFAICT, this is a place to ask this question. If not, please suggest another.

It is _a_ place, but not really _the_ place, as you've probably figured by the lack of response thus far.  This is a mailing list for SunPy, a Python package for solar physics data analysis.  I am not sure where a better place would be, though.  Guess you got lucky this time! :-)

cheers,

Derek

Thank you.

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[Benjamin Brink]

On 3/14/16 8:21 PM, Derek Lamb wrote:

>
>> On Mar 13, 2016, at 11:12 PM, Benjamin Brink wrote:
>>
>> Hi,
>>
>> How can one determine the relative orientation of the solar equator to
>> a position at Earth's core for a given time?
>
> Go to http://ssd.jpl.nasa.gov/horizons.cgi. Select the "Observer"
> Ephemeris type, "Sun" as the target body, "Geocentric" for the observer
> location, and in Table Settings make sure you have at least #14
> "Observer sub-lon & sub-lat" selected. If you select the default time
> range, you'll get today + 30 days, and you'll see the observer sub
> longitude is about -7.16 deg and increasing, which is correct: Earth is
> south of the solar equator at the moment.

Thank you! Now I have references to check calcs.

>
>> I've tried a few queries at JPL Horizon's, but am not seeing the 7+
>> degree difference at any time in a year's worth of data. My queries
>> are asking for something else. :-/
>
> You didn't say what was in your queries. Without knowing that, it's
> hard to guess what you were doing incorrectly.
>

For example:
Target body name: Earth (399) {source: DE431mx}
Center body name: Sun (10) {source: DE431mx}
Center-site name: BODYCENTRIC
with:
hEcl-Lon hEcl-Lat
or
Obsrv-lon Obsrv-lat
or
Sl-lon Sl-lat

>> AFAICT, this is a place to ask this question. If not, please suggest
>> another.
>
> It is _a_ place, but not really _the_ place, as you've probably figured
> by the lack of response thus far. This is a mailing list for SunPy, a
> Python package for solar physics data analysis. I am not sure where a
> better place would be, though. Guess you got lucky this time! :-)
>

Indeed. It's relevant to studying solar dynamics, and AFAICT, Python is
a bit like tcl --my preferred coding language. Not too far off ;-)

Thank you, Derek.