# pvlib.solarposition.declination_cooper69¶

pvlib.solarposition.declination_cooper69(dayofyear)[source]

Solar declination from Duffie & Beckman [1] and attributed to Cooper (1969)

Warning

Return units are radians, not degrees.

Declination can be expressed using either sine or cosine:

$\delta = 23.45 \sin \left( \frac{2 \pi}{365} \left(n_{day} + 284 \right) \right) = -23.45 \cos \left( \frac{2 \pi}{365} \left(n_{day} + 10 \right) \right)$
Parameters

dayofyear (numeric) –

Returns

declination (radians) (numeric) – Angular position of the sun at solar noon relative to the plane of the equator, approximately between +/-23.45 (degrees).

References

[1] J. A. Duffie and W. A. Beckman, “Solar Engineering of Thermal Processes, 3rd Edition” pp. 13-14, J. Wiley and Sons, New York (2006)

[2] J. H. Seinfeld and S. N. Pandis, “Atmospheric Chemistry and Physics” p. 129, J. Wiley (1998)

[3] Daryl R. Myers, “Solar Radiation: Practical Modeling for Renewable Energy Applications”, p. 4 CRC Press (2013)