Hello Mike,
This is a bit confusing because I'm not sure I can tell what type of
hour-lines are being considered here. Perhaps Ron was referring to the
fact that if one constructs the hour-lines from the projection of the
Analemma itself AND includes the delta in local longitude from the
longitude of the standard meridian, then, the solar projection will
indeed cross zero four times per year(?). I think this may be the more
intuitive way of constructing such a sundial too, for the very reason
that this thread makes clear.
Regards,
Luke Coletti
The Shaws wrote:
>
> Ron wrote:
> <<I've never built a ceiling dial, but something doesn't sound right about
> the advice that you got. The days that you choose should be days where the
> "equation of time is 0 (sun time and watch time agree). This happens 4
> times a year. April 15, June 14, Sept 1, Dec 25.>>
>
> But clocks and dials DON'T coincide on these dates UNLESS you just happen to
> live on your prime meridian.
>
> If you want to apply the "normal" Equation of Time correction, you will have
> to work out which days coincide at your own longitude.
> Where I live (3 degrees West of Greenwich) clock and dial only coincide on 2
> days a year.
> If you live more than about 5 degrees away from your meridian, they will
> never coincide.
>
> See:
> http://homepage.ntlworld.com/jmikeshaw/
> and follow the link to "Equation of Time slide rule" first,
> and then "Noon Mark"
>
> Mike Shaw
>
> N 53º 21' 24"
> W 03º 01' 47"
> Wirral, UK.
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.307 / Virus Database: 168 - Release Date: 11/12/2001
