Re: Astronomical coordinates

In article <43CAD338.6D1FA770@xxxxxxxxxxxxxxxxx>,
Jake <jakmal@xxxxxxxxxxxxxxxxx> wrote:

> Paul Schlyter wrote:
>>
>> In article <43C8918A.BA533D8A@xxxxxxxxxxxxxxxxx>,
>> Jake <jakmal@xxxxxxxxxxxxxxxxx> wrote:
>>
>>> Paul Schlyter wrote:
>>>>
>>>> In article <43C7D988.46F6843@xxxxxxxxxxxxxxxxx>,
>>>> Jake <jakmal@xxxxxxxxxxxxxxxxx> wrote:
>>>>> Paul Schlyter wrote:
>>>>>
>>>>>> In article <43C7084E.434C2110@xxxxxxxxxxxxxxxxx>,
>>>>>> Jake <jakmal@xxxxxxxxxxxxxxxxx> wrote:
>>>>>>
>>>>>>> Because I wanted to convert from celestial coordinates (aka equatorial
>>>>>>> coordinates) to heliographic coordinates, which AFAIK are always
>>>>>>> heliographic _ecliptic_ coordinates. I don't see the point of
>>>>>>> heliographic equatorial coordinates, although such an oddity may exist
>>>>>>> so maybe I should have been more specific.
>>>>>>
>>>>>> Your terminology seems a bit confused....
>>>>>>
>>>>>> First, the term "celestial coordinates" is vague and ambiguous - it merely
>>>>>> means something like "coordinates in the sky", and as you're aware of
>>>>>> there are several different ways to define such coordinates. Presumably
>>>>>> you mean geocentric equatorial coordinates.
>>>>>
>>>>> AFAIK "celestial coordinates" always refers to geocentric equatorial
>>>>> coordinates. I've never seen it used to refer to geocentric ecliptic
>>>>> coordinates.
>>>>
>>>> Check out:
>>>>
>>>> http://en.wikipedia.org/wiki/Celestial_coordinates
>>>
>>> I hope you don't routinely use wikipedia as a definitive source. It's
>>> not scholarly reviewed. For example, check out this silly account on
>>> Laplace's "sphere of influence" that defines it as both solar-specific
>>> and erroneously spherical:
>>>
>>> http://en.wikipedia.org/wiki/Sphere_of_influence_%28astrodynamics%29
>>>
>>> --
>>> Jake
>>
>> Wikipedia isn't the only source who doesn't think "Celestial Coordinates"
>> always is geocentric equatorial coordinates. Check out e.g.:
>>
>> http://archive.stsci.edu/fits/users_guide/node59.html
>>
>> This web page (which is hosted by the Space Telescope Science Institute)
>> mentions five different kinds of Standard Celestial Coordinates:
>>
>> - equatorial coordinates
>> - galactic coordinates
>> - ecliptic coordinates
>> - supergalactic coordinates
>> - helioeclipitic coordinates
>
> Incorrect. Celestial coordinates refer to the celestial sphere, which
> by definition is geocentric. Heliocentric ecliptic coordinates do not
> refer to the celestial sphere, hence are not celestial coordinates.

It said "helioecliptic", not "heliocentric". Helioecliptic
coordinates are geocentric. You can find the definition of
helioecliptic coordinates, and how it differs from normal ecliptic
coordinates, in this scholary reviewed paper:

http://www.atnf.csiro.au/people/mcalabre/WCS/ccs.pdf

> I agree that the definition may be stretched to include all geocentric
> systems,

....and not just geocentric systems: since no-one lives at the center
of the earth, all of us live on the Earth's surface, I see no reason
to not also include topocentric (= observer centered) coordinates
among the "celestial coordinates".

> but it most commonly refers to the most "natural" or logical of the
> geocentric systems: the equatorial coordinate system.

Dunno 'bout that -- one should use words like "natural" with some
caution. The most "natural" celestial coordinate system to the
average layperson here on Earth would most likely be horizontal
topocentric coordinates. Most people on Earth probably don't even
know what equatorial celestial coordinates is.

Anyway, since you demanded a "scholary reviewed" source from me, you
must have had scholars in astronomy (= professional astronomers) in
your mind. And the pro's frequently use other celestial coordinates
than equatorial coordinates.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
.

Relevant Pages

  • Re: Astronomical coordinates
    ... Wikipedia isn't the only source who doesn't think "Celestial Coordinates" ... always is geocentric equatorial coordinates. ... professional astronomers. ... pausch at stockholm dot bostream dot se ...
    (sci.astro)
  • Re: Astronomical coordinates
    ... >> Paul Schlyter wrote: ... >> I hope you don't routinely use wikipedia as a definitive source. ... > Wikipedia isn't the only source who doesn't think "Celestial Coordinates" ...
    (sci.astro)