Ross McCluney wrote: ..... > EOT = .170 sin (4*pi*(J - 80)/373) - .129 sin (2*pi*(J - 8).355) > > where the arguments of the sine functions are in radians and J is the > number of days since December 31, and EOT is given in decimals hours. > .....
Dear Ross, I received your formula for the EoT as above. I assume the last term must be ( J - 8 ) / 355. I was curious about this formula, because I didn't expect the numbers 373 and 355 on those places. I expected the number of days in a year. ( 365 or 365.25 ). So I calculated the results of the formula and my computer compared them with the results of my procedures. The + and - differences are shown below for the years 1997 - 2012. When you accept this accuracy you may use this formula during a long time. ( My value - your value ) 1997 19.38 sec at day 1.5 -45.34 sec at day 365.5 1998 26.37 sec at day 1.5 -38.26 sec at day 365.5 1999 33.37 sec at day 1.5 -31.17 sec at day 365.5 2000 40.39 sec at day 1.5 -24.30 sec at day 366.5 2001 19.12 sec at day 1.5 -45.61 sec at day 365.5 2002 26.10 sec at day 1.5 -38.54 sec at day 365.5 2003 33.10 sec at day 1.5 -31.45 sec at day 365.5 2004 40.12 sec at day 1.5 -24.57 sec at day 366.5 2005 18.86 sec at day 1.5 -45.89 sec at day 365.5 2006 25.83 sec at day 1.5 -38.82 sec at day 365.5 2007 32.83 sec at day 1.5 -31.74 sec at day 365.5 2008 39.85 sec at day 1.5 -24.84 sec at day 366.5 2009 18.59 sec at day 1.5 -46.16 sec at day 365.5 2010 25.57 sec at day 1.5 -39.10 sec at day 365.5 2011 32.56 sec at day 1.5 -32.02 sec at day 365.5 2012 39.57 sec at day 1.5 -25.12 sec at day 366.5 Lateron in the century the max error isn't always at the first or last day but can fall on another day. See example for 2097. 2097 26.41 sec at day 71.5 -52.29 sec at day 364.5 The change in the error from year to year shows the change in the real EoT, because your formula always give the same values. Don't look at the decimals, the computer just printed them as well. Fer J. de Vries.
