Compute the declination angle of the sun for the given date.

    Uses the Spencer Formula
    (found at http://www.illustratingshadows.com/www-formulae-collection.pdf)

    :param day: The datetime.date to compute the declination angle for
    :returns: The angle, in degrees, of the angle of declination

def sun_declination(day):
    """Compute the declination angle of the sun for the given date.

    Uses the Spencer Formula
    (found at http://www.illustratingshadows.com/www-formulae-collection.pdf)

    :param day: The datetime.date to compute the declination angle for
    :returns: The angle, in degrees, of the angle of declination
    """
    day_of_year = day.toordinal() - date(day.year, 1, 1).toordinal()
    day_angle = 2 * pi * day_of_year / 365
    declination_radians = sum([
        0.006918,
        0.001480*sin(3*day_angle),
        0.070257*sin(day_angle),
        0.000907*sin(2*day_angle),
        -0.399912*cos(day_angle),
        -0.006758*cos(2*day_angle),
        -0.002697*cos(3*day_angle),
    ])

    return degrees(declination_radians)