For the March Equinox:
JD = 1721139.2855 + 365.2421376 Y + 0.0679190 y^2 - 0.0027879 y^3
For the September Equinox:
JD = 1721325.6978 + 365.2425055 Y -0.1266890 y^2 + 0.0019401 y^3
where Y = the year ( 1996, 1997 etc) and y = Y/1000
After you have computed the above Julian Date, you can convert this data into a month, day and year using:
Add 0.5 to JD above.
Set I = integer part of JD
Set F = fractional part of JD
If I is larger than 2299160 calculate:
A = integer part of ( I - 1867216.25)/36524.25
B = I + 1 + A - integer part of (A/4)
otherwise, set A = I
Now calculate C = B + 1524
Calculate D = integer part of (C - 122.1)/365.25
Calculate E = integer part of 365.25 x D
Calculate G = integer part of ( C - E)/30.6001
Calculate d = C - E + F - integer part of (30.6001 x G)
This is the day of the month including its decimal fraction
Calculate m = G - 1 if G is less than 13.5
or m = G - 13 if G is more than 13.5
This is the month number
Calculate y = D - 4716 if m is more than 2.5
y = D - 4715 if m is less than 2.5
This is the year.
To predict the dates of the Winter and Summer Solstices, use the above procedure for the equinoxes, but with the Julian Dates defined as:
Summer:
JD = 1721233.2486 + 365.2417284 Y - 0.0530180 Y^2 + 0.0093320 Y^3
Winter:
JD = 1721414.3920 + 365.2428898 Y - 0.0109650 Y^2 - 0.0084885 Y^3
Copyright 1997 Dr. Sten Odenwald
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