Subject: Re: Velocity components

From: Peter R Newman <[email-masked]>
Date: 12 May 1998 08:43:06 -0500

Randy Stegemeyer wrote about his radio telescope:

First, a big well done on what you have so far!

>
>      What I want to do now is to correct the doppler shifts for the
> motion of the earth moving around the sun, and for the rotation of the
> earth itself.  I find all kinds of information on coordinate systems
> and converting between them, but I have not found any formulas for
> actually calculating the velocity components in various directions.
[snip]
>      If someone could direct to a reference, or provide the formulas
> themselves,

The book "Observational Astronomy" by D. Scott Birney (1991, Cambridge
University Press) gives a fairly complete guide to the reduction of
radial velocities on pages 216-223.  This is a good undergraduate level
text in general, although primarily aimed at optical observations.

Also, I think any edition of the Astronomical Almanac (a US Naval
Observatory/HMSO publication) will give the equations you need, plus all
the constants, but I don't have a copy to hand to check.

Good luck, and do continue to publish your results!

Pete
-- 
http://sa1.star.uclan.ac.uk/~prn
Happy is he who has been able to learn the causes of things - Virgil

---

From: [email-masked] (John Chandler)
Date: 12 May 1998 08:48:18 -0500

Randy Stegemeyer ([email-masked]) wrote:
:      What I want to do now is to correct the doppler shifts for the
: motion of the earth moving around the sun, and for the rotation of the
: earth itself.

What about the motion of the Sun with respect to the LSR or the LSR
with respect to the Galaxy or...  Even leaving those aside, the
question is not so simple.  You have to specify what level of
precision you want, in order to know what sorts of approximations will
be acceptable (and you probably want to use all the approximations you
can).  For example, the rotational velocity on the Earth's surface is
less than .5 km/s -- if you don't need the velocity to that level, you
can ignore the rotation entirely.

--
John F. Chandler             [email-masked]