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Re: How to look up historical time zones by date and location

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  Re: How to look up historical time zones by date and location Joel Goldstick <joel.goldstick@gmail.com> - 2014-08-18 09:51 -0400
    Re: How to look up historical time zones by date and location Rustom Mody <rustompmody@gmail.com> - 2014-08-18 08:41 -0700
    Re: How to look up historical time zones by date and location pecore@pascolo.net - 2014-08-18 22:31 +0200

#76477 — Re: How to look up historical time zones by date and location

On Mon, Aug 18, 2014 at 9:12 AM, luofeiyu <elearn2014@gmail.com> wrote:
> I found that it is a concept LMT local mean time can express my meaning.

Local Mean Time is time based on the actually astronomical position of
the sun.  It is defined as 12 noon when the sun is at its high point,
directly south in the sky.  This is the time you get when you read a
sundial!
So each town or village set their clocks differently.  That all
changed with the railroad industry.  Once trains began traveling, time
zones were invented so that everyone knew exactly what time it was in
order to keep trains from meeting on the same tracks and colliding.
Trains need time schedules.  Time zones make this possible.

Since the advent of time zones, you can be pretty well assured that
the your LMT will be within a half hour or so (east or west) of the
Time zone your location is assigned.  But time zones are drawn for
political reasons, and so that may not be precisely the case.  In
Indiana, USA there are (or were) several regions in different time
zones.   In the summer, they would change again, but not in step, so
some places didn't switch to 'daylight savings time', and some did.
Again, this had mostly to do with who the local business did business
with, to keep time common for common trading partners.

Off topic --  please remember to use plain text.


>
> import pytz,datetime
> tz1 = pytz.timezone('Asia/Shanghai')
> tz1
> <DstTzInfo 'Asia/Shanghai' LMT+8:06:00 STD>
>>>> str(tz1)
> 'Asia/Shanghai'
>
> tz2 = pytz.timezone('Asia/Urumqi')
> tz2
> <DstTzInfo 'Asia/Urumqi' LMT+5:50:00 STD>
>
> the time difference between shanghai and Urumqi is about 2 hours in the form
> of LMT.
>
> now ,how can i get the output of `LMT+8:06:00` in <DstTzInfo 'Asia/Shanghai'
> LMT+8:06:00 STD>
>
> str(tz1) or str(tz2) can not do that.
>
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>



-- 
Joel Goldstick
http://joelgoldstick.com

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#76483

On Monday, August 18, 2014 7:21:53 PM UTC+5:30, Joel Goldstick wrote:
> On Mon, Aug 18, 2014 at 9:12 AM, luofeiyu  wrote:
> > I found that it is a concept LMT local mean time can express my meaning.

> Local Mean Time is time based on the actually astronomical position of
> the sun.  It is defined as 12 noon when the sun is at its high point,
> directly south in the sky.  This is the time you get when you read a
> sundial!
> So each town or village set their clocks differently.  That all
> changed with the railroad industry.  Once trains began traveling, time
> zones were invented so that everyone knew exactly what time it was in
> order to keep trains from meeting on the same tracks and colliding.
> Trains need time schedules.  Time zones make this possible.

Add to that the fact that any two places even say a kilometer apart,
will have different LMT.
Naturally if one chooses a least count, say 1 sec, then that distance will 
be larger.

40075 km equatorial circumference
86400 secs in a day (60×60×24)

40075/86400 = 2.1 

ie LMT changes by 1 sec for every 2.1 km E-W along the equator

And even here the distance would shrink going towards the poles.

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#76509

Joel Goldstick <joel.goldstick@gmail.com> writes:

> Local Mean Time is time based on the actually astronomical position
> of the sun.  It is defined as 12 noon when the sun is at its high
> point, directly south in the sky.  This is the time you get when you
> read a sundial!

a sundial measures the Apparent Time, where the duration between two
consecutive noons is different from 24*3600 s due to the variations in
the Sun apparent angular velocity, that are originated by the Earth's
orbit eccentricity and by the inclination of the Earth's rotation
axis

these variation are small but cumulative, so the AT can be fast or
slow with respect to the LMT by as much as ±15'

don't know if the same considerations apply also in Urumqi

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