Failure to calculate equation of time and declination of the sun

[dwaynie]

Calculating the equation of time and the declination of the sun

Hi,

I'm trying to calculate the equation of time and the declination of the sun in the prettiest way possible:

https://gist.github.com/1278755"

But right now I'm getting some unexpected values:

1) Failure:
test_suns_declination(TestSolarCalculations):
Expected -3.18, not -0.8773192601265396.

2) Failure:
test_equation_of_time(TestSolarCalculations):
Expected 2011-10-01 10:23:00 +0100, not 301.80925318673167.

Can anybody see what's wrong?

--Dwayne

 

[dwaynie]

Getting closer, still one month off though:

1) Failure:
test_equation_of_time(TestSolarCalculations):
Expected 2011-10-01 10:23:00 UTC, not 2011-10-28 17:02:35 UTC.

2) Failure:
test_suns_declination(TestSolarCalculations):
Expected -3.18, not 1.380604820284565.

 

[BobG]

When your computer calculates sine and cosine, is it calculating trig functions for an angle in radians or an angle in degrees?

(Excel, for example, has to have the angles converted into radians before calculating the sine or cosine.)

 

[dwaynie]

Cool! So I added a degrees to radians converter. But whereas my declination of the sun is getting really close, my equation of time has gotten way off by 10 months!

1) Failure:
test_equation_of_time(TestSolarCalculations):
Expected 2011-10-01 10:23:00 UTC, not 2011-01-06 01:08:11 UTC.

2) Failure:
test_suns_declination(TestSolarCalculations):
Expected -3.18, not -3.2087920449753007.

Any ideas? I hope my script remains readable.

https://gist.github.com/1278755"

Have you seen this by the way?

http://www.youtube.com/watch?v=y2R3FvS4xr4"

--Dwayne

 

[dwaynie]

I realized I forgot to convert my sun's mean longitude back to degrees before calculating the equation of time. Now I'm back to being just a month off.

1) Failure:
test_equation_of_time(TestSolarCalculations):
Expected 2011-10-01 10:23:00 UTC, not 2011-10-28 10:59:31 UTC.

2) Failure:
test_suns_declination(TestSolarCalculations):
Expected -3.18, not -3.2087920449753007.

--Dwayne