From: Xavier Noria <fxn@...>
Date: 2010-08-27T19:14:47+09:00
Subject: Re: Time.local and offsets

On Fri, Aug 27, 2010 at 12:11 PM, Brian Candler <b.candler@pobox.com> wrote:

> Brian Candler wrote:
>>>> Time.parse("1 jan 1847")
>> => Fri Jan 01 00:00:00 -0001 1847
>>>> Time.parse("1 jan 1848")
>> => Sat Jan 01 00:00:00 +0000 1848
>>>> Time.local("1847").utc_offset
>> => -75
>>>> Time.local("1848").utc_offset
>> => 0
>>
>> Sorry, I can't explain that one. I've heard of half-hour time zones and
>> even quarter-hour ones, but not a minute and a quarter :-)
>
> I think I have it:
> http://en.wikipedia.org/wiki/Time_zone
>
> It wasn't until 1847 that Greenwich Mean Time was widely used across the
> UK. Before then, everyone used "solar time", which means that clocks at
> different points of the country (east to west) hit noon at different
> times. The difference would be 60 minutes for every 15 degrees of
> longitude.
>
> So if you were standing at St Paul's Cathedral, say, noon would be
> slightly later compared to noon in Greenwich, which is a bit to the
> East.
>
> In your case: Madrid has a longitude of 3 degrees 42 mins West. So the
> offset of Madrid solar time from GMT is:
>
> irb(main):001:0> -(3.0 + 42.0/60.0) / 15.0 * 60.0
> => -14.8
>
> and that's exactly what you saw. tzdata rules :-)

Awesome!!!

Thank you very much :)