Re: Sideral Time

From: Chris L Peterson (clp_at_alumni.caltech.edu)
Date: 03/03/05 

Date: Thu, 03 Mar 2005 13:38:44 GMT

On Thu, 3 Mar 2005 08:49:13 +0100, Paul Schlyter
<pausch.NO@SPAM.saaf.se> wrote:

>However, local time usually refers to the time at some time zone you
>reside in. That makes it more complicated for the watch to translate
>local time to sidereal time -- besides the GPS one would need time zone
>border information programmed into the watch, plus the rules about when
>to start and end daylight savings time in different parts of the world.
>Plus the ability to modify this information whenever political decisions
>change the time zone, or the daylight savings time rules (both have been
>changed due to political decisions within the last 10-15 years).

Well, since the OP asked for "local apparent sidereal time", none of
this matters. All you need is the longitude and the universal time, both
of which a GPS will provide nicely.

>Finally, a GPS receiver has one major drawback here: it won't work
>indoors. And it may not work well outdoors either, if you're in
>a city with tall buildings, or in the country inside a forest.

Many GPS units now work fairly well indoors, and almost certainly work
under a heavy forest canopy (and with the new satellite block, this will
only get better). I've been doing some development work on a project to
track stolen material, and what these devices are capable of is
remarkable. However, there isn't actually any need for the GPS unit to
work all the time if you want to use if to make a sidereal watch. The
GPS can be used to control and train an ordinary sidereal clock. Unless
you travel for miles underground, it is likely that you will have
moments of GPS coverage that allow the clock to get corrected. That's
how the emergency location system (E911) of some cell phones works- if
you are inside a building dense enough to block the GPS, the phone
simply takes your location as the outside of the building- the last
place it got a location signal.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

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