Re: [APML] Calculating time zone offset

[Gene Horr <genehorr@texas.net>]

"Leo S." wrote:
> 
> I am trying work out how to set my time zone offset for my mount.
> 
> Can someone please tell me if i have worked this out correctly - im pretty
> sure the answer i have got is wrong!?!
> 
> my Lat. is  50.52N
> my Long. is 4.25W
> 
> I've divided my Long. by 15 which gives:
> 
> 4.25/15 = 0.28333
> 
> My GMT offset is 0 so :
> 
> 0.28333 - 0 = 0.28333
> 
> ...but in the final calculation i have to multiply x15 which gets me back
> to 4.25 ?!!!
> 
> 0.28333 x 15 = 4.25

The reason is because you are in the "first" time zone.  So your offset is
your longitude.  What you are trying to find is how far away you are from
the 1 hour "time zone" (there's probably a technical term for it, but I don't
know what it is.)  Here's a comparison between your location and one in the
"second time zone":

Longitude	GMT Offset	Time Zone Offset

 4.25		0		4.25
19.25		1		4.25

Both locations are 4.25 degrees west of the time zone "edge".  But since
your "edge" is valued at zero, your longitude is your offset.

Rather than go by the divide by/multiply by 15 method IMO an easier way is
to just take your longitude - 15 * (GMT Offset).  IMO this better describes
what you are doing.

Additional useless information - the divide by 15 comes from 360 degrees /
24 time zones = 15 degrees/time zone.

Gene Horr
genehorr@texas.net

--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>