fer j. de vries wrote:
> Tad Dunne added to look to the most accurate sundial and with correction
> for the equation of time.
> To my opinion a dial with EoT correction can't be a winner.
>
> Suppose I have 2 dials with in principle the same accurate scale and the
> same type of shadow casting device, one for real suntime and one for
> civil time, thus with EoT correction.
> In that case I prefer the dial for suntime.
>
> The one with EoT correction has in a 4 years period errors in the
> reading by the change of the EoT, unless if I callibrate the sundail
> every year.
> For example at 26 december the EoT in 4 years varies between -9 and -46
> seconds of time. This gives an error in the reading also.
> In further future the EoT changes and with it new errors occur in the
> reading of the dial.
>
> The sundial for suntime automatically corrects for the EoT..........
> This also is the reason why suntime hours are unequal of length.....
> This sundial has a 'built in corrector' for this and always uses the
> correct length of each hour.
Fer,
You mention above that for 12-26 there is a variation in the EoT
between -9 and -46 seconds, a 37 sec delta, over a four year period. Which
4 year period did you calculate for? I have calculated and included below
both the solar day length and EoT values for 12-26 over a twenty year
period. The max delta between succeeding EoT values and the 1995 value,
column G, over the twenty year period reaches 23.5 secs in 2012. It can also
be seen that on periods of four years from the starting point in 1995 the
delta reaches only 1.6 secs after twenty years! I used the 1995 USNO
formulas as listed in section C page 24. Perhaps you can let me know which
methods you used to calculate the 37 sec delta and over what period.
Regards,
Luke Coletti
Columns:
A: number of days in the given year
B: year
C: day of year evaluated
D: number of days from J2000
E: solar day length of evaluated day (secs)
F: EoT value at evaluated day (secs)
(solar day length & EoT = TA-TM @12h UT)
G: delta between evaluated EoT value
and 1995 value (secs) i.e., Fn-F1
A | B | C | D | E | F | G
------------------------------------------------------------
365 1995 360 -1467.5 -29.7542 -7.9874 +0.000000
366 1996 361 -1101.5 -29.6892 -30.3253 -22.337959
365 1997 360 -736.5 -29.7112 -22.9917 -15.004361
365 1998 360 -371.5 -29.7312 -15.6522 -7.664840
365 1999 360 -6.5 -29.7492 -8.3073 -0.319886
366 2000 361 +359.5 -29.6835 -30.6409 -22.653520
365 2001 360 +724.5 -29.7057 -23.3088 -15.321366
365 2002 360 +1089.5 -29.7259 -15.9706 -7.983245
365 2003 360 +1454.5 -29.7441 -8.6270 -0.639645
366 2004 361 +1820.5 -29.6779 -30.9563 -22.968932
365 2005 360 +2185.5 -29.7003 -23.6256 -15.638229
365 2006 360 +2550.5 -29.7207 -16.2889 -8.301515
365 2007 360 +2915.5 -29.7390 -8.9467 -0.959276
366 2008 361 +3281.5 -29.6722 -31.2716 -23.284193
365 2009 360 +3646.5 -29.6948 -23.9423 -15.954950
365 2010 360 +4011.5 -29.7153 -16.6070 -8.619649
365 2011 360 +4376.5 -29.7339 -9.2662 -1.278779
366 2012 361 +4742.5 -29.6665 -31.5867 -23.599304
365 2013 360 +5107.5 -29.6892 -24.2589 -16.271527
365 2014 360 +5472.5 -29.7100 -16.9250 -8.937647
365 2015 360 +5837.5 -29.7288 -9.5855 -1.598154
