[time-nuts] Information on the Danjon Astrolab

[Magnus Danielson]

From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] Information on the Danjon Astrolab 
Date: Tue, 08 Aug 2006 08:33:32 +0000
Message-ID: <53594.1155026012 at critter.freebsd.dk>

> In message <20060808.102323.-861060158.cfmd at bredband.net>, Magnus Danielson wri
> tes:
> 
> >> You would really need to know the direction of local gravity for
> >> this to be any good...
> >
> >Down? :-)
> 
> There's a big difference between "down enough that cows don't easily
> tip over" and "passes through the center of the earth".

Hence the smiley.

> I know the Carlsberg Meridian had to take it into account when
> it was moved down to the Canary Islands.

Ofcourse they would have to, they moved down on the longitude on an ellipsoid
and then ofcourse they have a different local gravity and the gradient of that
will differ (and hence the angle of the gravity will differ slightly from that
of the normal on the ellipsoid). Ever looked at a gravity map of the earth?

> >Wouln't a number of measurements and comparision with other methods and
> >measurements help to reveal such deviations? Then again, question is if the
> >deviation is so large that it has a real impact.
> 
> Obviously, it all depends how precise you want it.

Indeed.

Cheers,
Magnus