converting star coordinates to x,y,z

I'm working on a project of modeling the stars of the constellations in
3-D; not for their positions relative to Earth, but relative to any
given person being at 0,0,0.

Is there a simple formula for this? ...or better yet, do you know
anyone who has them on the net or in a book?

Thanks!

Rick.

wrote:
I'm working on a project of modeling the stars of the constellations in
3-D; not for their positions relative to Earth, but relative to any
given person being at 0,0,0.

Is there a simple formula for this? ...or better yet, do you know
anyone who has them on the net or in a book?

It's going to be very messy. Star positions practically BEG for
spherical coordinates, (which is what they are really), so converting to
Cartesian you are looking for trouble.

I don't know if anyone has been masochistic enough to try it, but you
could conceivably do it. Open any Calculus book and apply the conversion
formulas found there, although I suspect that you'd be better off if you
situated Earth's center at (0,0,0). That way, you avoid the problem of
those coordinates changing (even more slightly) everytime the season
changes and the observer's position changes on the surface of the Earth.

Since the celestial dome appears "spherical", be prepared to be
bombarded with thousands of sin's and cos's.

Good luck!

Thanks!

Rick.
--
I. N. G. --- http://users.forthnet.gr/ath/jgal/

Clarification:
I see that I too hastily posted the question. 0,0,0 would be Earth.
The
figure for 'x' would need to be the distance from Earth, with y and z
being
taken from RA and DEC...is that right?

If we use the stars of Orions belt as an example, can you help me put
them
to x,y,z?

Alnitak: 400ly, RA 05 40 45.5, DEC -01 56 34
Alnilam: 1340ly, RA 05 36 12.7, DEC -01 12 07
Mintaka: 600ly, RA 05 32 00.3, DEC -00 17 57

PS: I AM a masochist and will do what it takes to create these models.
I appreciate any and all of who will hang in there with me on this. It
will be so cool!
(Am I the only one who thinks so??)
Rick.

wrote:
I'm working on a project of modeling the stars of the
constellations in
3-D; not for their positions relative to Earth, but relative to any
given person being at 0,0,0.

Is there a simple formula for this? ...or better yet, do you know
anyone who has them on the net or in a book?

Ioannis responded:

It's going to be very messy. ...
Since the celestial dome appears "spherical", be prepared to be
bombarded with thousands of sin's and cos's.

Yikes! You make this sound like a major undertaking; it's actually
a problem in elementary trigonometry that any kid in a high-school
pre-calculus class should be able to solve in 5 minutes.

Conversion from RA/Dec to rectangular coordinates requires two sines
and two cosines -- or two and three, depending how you count.

My only question is about the meaning of the phrase "relative not to
Earth but to a person at 0,0,0". I've been searching for 0,0,0 all
my life, and I still haven't found it!

- Tony Flanders

wrote in message
ups.com...
I'm working on a project of modeling the stars of the constellations in
3-D; not for their positions relative to Earth, but relative to any
given person being at 0,0,0.

Search for the program "Celestia" on Google and download it. It's free. It
knows both the direction (RA and Dec) *and* distance (LY) of many stars and
allows you to position yourself anywhere in 3D space and see how things look
from there. If you go to the Navigation / StarBrowser menu item it brings up
a list of up to 500 stars giving, among other things, their distance in LY
from earth. Using these 3 polar coordinates (RA, Dec, LY) for any star you
can transform these polar coordinates into Cartesian coordinates (probably
using Z-axis is declination 90 degrees, X-axis is RA of zero hours, Y-axis
is RA of 6 hours). With these 3 computed X, Y, Z coordinates you would then
subtract a translation vector (delta-X, delta-Y, delta-Z) of a viewpoint
somewhere other than earth and you now have the X, Y, Z coordinates of your
chosen star *relative* to the new viewpoint.

Unfortunately, Celestia does not show you any of its own mathematics, but
this is essentially what it's doing.

I'm working on a project of modeling the stars of the constellations in
3-D; not for their positions relative to Earth, but relative to any
given person being at 0,0,0.

And WHERE is the location of 0,0,0 exactly???
Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

wrote:
[snip]
Ioannis responded:


It's going to be very messy. ...
Since the celestial dome appears "spherical", be prepared to be
bombarded with thousands of sin's and cos's.


Yikes! You make this sound like a major undertaking; it's actually
a problem in elementary trigonometry that any kid in a high-school
pre-calculus class should be able to solve in 5 minutes.

Conversion from RA/Dec to rectangular coordinates requires two sines
and two cosines -- or two and three, depending how you count.

My only question is about the meaning of the phrase "relative not to
Earth but to a person at 0,0,0". I've been searching for 0,0,0 all
my life, and I still haven't found it!

My impression was that he wanted a conversion for a person situated on
the surface of the Earth for EACH such position.

Since there are going to be so many such positions (taken as 0,0,0), I
thought he wanted a model that would simultaneously provide for every
position, as the Earth rotates.

For example, what are the rectangular coordinates of Alnitak with 0,0,0
taken at my position in Spring in Athens and at your position in Winter?

If this wasn't the case, I seem to have misunderstood him.

- Tony Flanders
--
I. N. G. --- http://users.forthnet.gr/ath/jgal/

I don't want to be negative but its not that hard. Its not a three
dinensional
problem but a 2-dimensional problem.

I do believe that the person said x,y,z, which means that distance from 0,0,0
would count. That makes it 3-D. Though of course the display itself might be
2-d or the person might have a new sort of display in mind that shows true
depth as well as width and height.

Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

Check out the books by Jean Meeus - there may be something there you could
adapt for your purpose.
Clear, Dark, Steady Skies!
(And considerate neighbors!!!)