[time-nuts] telling time without a clock

Neville Michie namichie at gmail.com
Sat Jan 28 18:14:03 EST 2012

Surely the proximity of the Moon to the surface of the Earth
makes the timing of an occultation dependent on where you are on the  
Earth's surface. (Parallax error)
The calculations to correct for this must make it a mathematicians  
Nevil Maskelyne, tormentor of John Harrison, advocated "lunar  
distances" but it was not practical,
as is demonstrated by it never being used.

Telling the time on the Earth's surface was commonly done with a sun  
dial, and these can be refined to a fraction
of a minute. With about 30 years of observations this should be able  
to discipline an atomic clock to a second or better,
and reach the limit of stability of the atomic clock.

cheers, Neville Michie

On 29/01/2012, at 3:46 AM, aartmolsen at comcast.net wrote:

> The star catalog specifically designed for lunar occultations is  
> the XZ (I'm guessing it stands for eXtended Zodiacal) Catalog from  
> the US Naval Observatory. It's based on the earlier ZC and covers  
> the band of brighter stars that can be occulted by the moon. Simbad  
> should have these catalogs.
> Aart Olsen
> ----- Original Message -----
> From: "Chris Albertson" <albertson.chris at gmail.com>
> To: jfor at quikus.com, "Discussion of precise time and frequency  
> measurement" <time-nuts at febo.com>
> Sent: Thursday, January 26, 2012 10:42:00 PM
> Subject: Re: [time-nuts] telling time without a clock
> "simbad" is a catalog of catalogs with a built in web based search
> engine. It is pretty much what "everyone" uses to search. You can
> define a shape and ask for all objects that meet some criteria that
> are within that shape. Other software can plot the result for you as
> a chart If it is not in Simbad you have likely discovered something
> new.
> http://simbad.u-strasbg.fr/simbad/
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