# Unit vector to Right Ascension/Declination

1. Feb 20, 2013

### 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.

#### Attached Files:

• ###### UNIT VECTOR.jpg
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2. Feb 20, 2013

### 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?

3. Feb 20, 2013

### Scott S

4. Feb 20, 2013

### 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 [Broken]

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.

Last edited by a moderator: May 6, 2017
5. Feb 20, 2013

### Scott S

Got it, thanks.

Wrong formulae.

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