Unit vector to Right Ascension/Declination

[Scott S]

OK, I'm really rusty on this.

I need to convert a unit vector to right ascension and declination.
I believe I recall the formulae correctly, as I seem to have gotten 1 as my radius.
So, that's good.

In the pic I have my unit vector (P2), my actual answer below, my expected answer in red and the formulae I (believe) I need in blue shaded cells.

Any help greatly appreciated.

 

[chiro]

Hey Scott S.

Can you point out a wiki or some other resource that outlines the concept you are talking about for ascension and declination?

 

[Scott S]

Right, sorry.
Right Ascension and Declination are spherical coordinates for stars etc., where declination equals latitude and right ascension longitude.

http://en.wikipedia.org/wiki/Celestial_coordinate_system

 

[chiro]

A quick google search gave me this which discusses a lot of common transformations.

http://www2.astro.psu.edu/users/rbc/a501/positional_astronomy.pdf

If you wanted to derive the results yourself you should derive the metric tensor that goes between two systems and check if the tensor you derive gives the same results.

The metric tensor is related to the Jacobian transformation between the two systems and you can learn it by reading about tensor mathematics or differential geometry.

 

[Scott S]

Got it, thanks.

Wrong formulae.