Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!rutgers!usc!wuarchive!emory!athena.cs.uga.edu!mcovingt
From: mcovingt@athena.cs.uga.edu ( Michael A. Covington)
Newsgroups: sci.electronics
Subject: Re: Sidereal Time Clock
Message-ID: <1990Dec13.045944.15919@athena.cs.uga.edu>
Date: 13 Dec 90 04:59:44 GMT
References: <1833@umriscc.isc.umr.edu> <1990Dec12.214854.19076@swbatl.sbc.com> <10633@uhccux.uhcc.Hawaii.Edu>
Distribution: sci.electronics
Organization: University of Georgia, Athens
Lines: 21

In article <10633@uhccux.uhcc.Hawaii.Edu> ressler@galileo.ifa.hawaii.edu (Mike "IR" Ressler) writes:
>In article <1990Dec12.214854.19076@swbatl.sbc.com> ken@swbatl.sbc.com (Ken Gianino 5-9081) writes:
>>In article <1833@umriscc.isc.umr.edu> robf@mcs213j.cs.umr.edu (Rob Fugina) writes:
>>>The clock has to count from 00:00:00 to 23:56:03, then reset back to zero.
>>
>> Why 23:56:03?   Doesn't sidereal time use 24 hours and just lose 4 min/day?
>
>I'm glad someone caught this. Sidereal time is indeed at 24 thing, it's just
>that the hours are slightly shorter - 1.002737909 times shorter (23h 56m
>4.09053s to the sidereal day). You just need to design a normal 24 hour clock
>that uses a clock frequency shifted up by this amount. Very vague
>recollections say that someone actually made 1.002738 MHz crystals, but I have
>no idea who. Good luck.

You are right. Sidereal time (defined as the right ascension of the meridian)
does go from 00:00 to 24:00 just like ordinary time; the units (day, hour,
minute, second, etc.) are a wee bit shorter.

There are many companies, such as JAN Crystals, that will custom-grind a
crystal to *any* frequency for under $10. Look in the back of any
electronics magazine.