archive: SETI Re: Doppler Shift

SETI Re: Doppler Shift

Walt Williams ( (no email) )
Sat, 22 Aug 1998 16:53:53 +0000

Hello David,

I am puzzled. What does this mean?

>>DW
The catch here is that the moon doesn't actualy orbit the earth, but,
to a two body approximation, the centre of gravity of the earth moon
system, which I estimate to be within the earth but fairly near the
surface.

Especially the moon part?

Would you please explain this again for me?

Thank you.

Walt Williams, 98.08.22
dfheli@pacificne.net
============================================

------- Forwarded Message Follows -------
From: David Woolley <david@djwhome.demon.co.uk>
Subject: Re: SETI Doppler Shift
To: n6tx@setileague.org (Dr. H. Paul Shuch)
Date: Sat, 22 Aug 1998 00:41:19 +0100 (BST)
Cc: seti@sni.net

>
> At 23:54 08/19/1998 +0100, David Woolley wrote:
>
> >
> >I'd therefore say that the galactic component can be ignored from a
> >chirp point of view.

On the other hand, there is another component that is not ignorable,
for some purposes, the one due to the earth moon system. The catch
here is that the moon doesn't actualy orbit the earth, but, to a two
body approximation, the centre of gravity of the earth moon system,
which I estimate to be within the earth but fairly near the surface.

I think this will be around 1,000 to 1,500 down on the equatorial
value for the earth's rotation for chirp rate, although only 30 to 50
down for peak to peak excursion. As such it would be on the edge of
detectability for a drift scan system at the 50 (or was it 20) mHz
bandwidth suggested as a practical limit.