Re: length of day

Paul: I appreciate the time you've taken to seriously deal with my question
(as opposed to dismissing it with an argument based on the equation of
time).

Is there a program out there that I can use to get accurate times for
sunrise/sunset? If your calculations are correct, then obviously I cannot
depend on the one I've been using.

Jeff



"Paul Schlyter" <pausch.NO@xxxxxxxxxxxx> wrote in message
news:1115476273.41fb1e534f0666649efedf5ada8f2710@xxxxxxxxxxx
> In article <H56dnalyy_lMueHfRVn-og@xxxxxxxxxx>, jeff-n@xxxxxxxxxx
> says...
>>Paul: Thank you for responding. Here are some data, as you requested:
>>
>>2005
>>Vernal equinox is Mar. 20. Sunrise is 7:21, sunset 7:29, interval is
>>12:08.
>>Autumnal equinox is Sept. 22. Sunrise is 7:04, sunset 7:16, interval is
>>12:12.
>>
>>2006
>>Vernal equinox is Mar. 20. Sunrise is 7:22, sunset 7:29, interval is
>>12:07.
>>Autumnal equinox is Sept. 23. Sunrise is 7:05, sunset 7:15, interval is
>>12:10.
>>
>>2007
>>Vernal equinox is Mar. 21. Sunrise is 7:20, sunset 7:30, interval is
>>12:10.
>>Autumnal equinox is Sept. 23. Sunrise is 7:05, sunset 7:15, interval is
>>12:10.
>>
>>2008
>>Vernal equinox is Mar. 20. Sunrise is 7:21, sunset 7:29, interval is
>>12:08.
>>Autumnal equinox is Sept. 22. Sunrise is 7:05, sunset 7:16, interval is
>>12:11.
>>
>>2009
>>Vernal equinox is Mar. 20. Sunrise is 7:21, sunset 7:29, interval is
>>12:08.
>>Autumnal equinox is Sept. 22. Sunrise is 7:04, sunset 7:16, interval is
>>12:12.
>>
>>Jeff Nadir
>
> First, a quote of your original question:
>
> # A table of sunrise/sunset times for Toronto shows that the interval
> # between sunrise and sunset is always a few minutes longer on the first
> # day of autumn than on the first day of spring. Why?
>
> Your own figures above show that this does not ALWAYS happen, not even
> in the table you used. It didn't happen in 2007 for instance...
>
> Next, we need the longitude, latitude and time zone of Toronto. From
> a world atlas I got:
>
> Lon 79d 20' W
> Lat 43d 39' N
>
> Timezone Eastern Time which is UT-5h winter time and UT-4h summer Time
>
> Next we check when the equinoxes did occur. In UT we get:
>
> March eq. September eq.
>
> 2005 March 20, 12:34 Sept 22, 22:23
> 2006 March 20, 18:26 Sept 23, 04:03
> 2007 March 21, 00:07 Sept 23, 09:51
> 2008 March 20, 05:48 Sept 22, 15:44
> 2009 March 20, 11:44 Sept 22, 21:19
>
> Let's convert this to Toronto time by subtracting 4 or 5 hours (it's
> DST on the September equinox but not on the March equinox):
>
> 2005 March 20, 08:34 Sept 22, 17:23
> 2006 March 20, 14:26 Sept 22, 23:03
> 2007 March 20, 20:07 Sept 23, 04:51
> 2008 March 20, 01:48 Sept 22, 10:44
> 2009 March 20, 07:44 Sept 22, 16:19
>
>
> I computed rise/set times myself for Toronto for your dates, and got
> these results (your figures appear within parentheses):
>
> 2005
> Mar 20 Sunrise 6:20 (7:21) set 18:30 (7:29) interval is 12:10 (12:08)
> Sep 22 Sunrise 7:05 (7:04) set 19:14 (7:16) interval is 12:09 (12:12)
>
> 2006
> Mar 20 Sunrise 6:21 (7:22) set 18:30 (7:29) interval is 12:09 (12:07)
> Sep 23 Sunrise 7:05 (7:05) set 19:13 (7:15) interval is 12:08 (12:10)
>
> 2007
> Mar 20 Sunrise 6:21 (----) set 18:29 (----) interval is 12:08 (-----)
> Mar 21 Sunrise 6:19 (7:20) set 18:31 (7:30) interval is 12:12 (12:10)
> Sep 23 Sunrise 7:05 (7:05) set 19:13 (7:15) interval is 12:08 (12:10)
>
> 2008
> Mar 20 Sunrise 6:20 (7:21) set 18:30 (7:29) interval is 12:10 (12:08)
> Sep 22 Sunrise 7:05 (7:05) set 19:14 (7:16) interval is 12:09 (12:11)
>
> 2009
> Mar 20 Sunrise 6:20 (7:21) set 18:30 (7:29) interval is 12:10 (12:08)
> Sep 22 Sunrise 7:05 (7:04) set 19:14 (7:16) interval is 12:09 (12:12)
>
> As you can see, in my computations the effect you reported vanishes
> and gets replaced with an opposite effect - the interval appears to
> be smaller during the "first day of autumn", but only by a minute
> so it could very well be a round-off effect or something. The only
> exception is the year 2007 - but in the year 2007 you selected March 21
> as "the first day of the spring" even though the March equinox occurred
> on March 20, Toronto time (but on March 21, Universal Time). If I in
> 2007 use March 20 instead, I get an exact match to the minute!
>
>
> So my explanation to the effect you reported is that it's due to some
> fairly small but systematic errors on the computation of the sunrise/set
> time in the table you consulted. What kind of errors? I don't know, it
> could be a lot of different things. And to try to find that out, you
> must contact the people responsible for those computations. If you
> don't want to trouble yourself with that, just consider that table
> somewhat unreliable.
>
>
>
>>--------------------------
>>
>>
>>"Paul Schlyter" <pausch.NO@xxxxxxxxxxxx> wrote in message
>>news:1115405917.357764c13b81d150dff7eb0e9661b432@xxxxxxxxxxx
>>> In article <LZCdnQKm9KoL5ebfRVn-pw@xxxxxxxxxx>, jeff-n@xxxxxxxxxx
>>> says...
>>>>Ray,
>>>>
>>>>Thanks for responding to my post so quickly and clearly.
>>>>
>>>>I know about the equation of time. I think I understand how the
>>>>variation
>>>>between sundial time and regular time affects the times of sunrise and
>>>>sunset given in the tables.
>>>>
>>>>What I don't understand is why the equation of time should affect the
>>>>INTERVAL between sunrise and sunset. If sundial and regular times differ
>>>>by
>>>>x minutes on the day of the vernal equinox shouldn't this just shift the
>>>>times of sunrise and sunset equally by x minutes in the same direction
>>>>leaving the length of the day unaffected? If sundial and regular time
>>>>differ
>
> --
> Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
> e-mail: pausch at saaf dot se
> WWW: http://stjarnhimlen.se/
> http://home.tiscali.se/pausch/


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