import math


def solar_declination(doy):
    """Solar declination for the day of the year in radians
    
    Example (1 October is the 274th day of the year):
    >>> print("%.6f" % solar_declination(274))
    -0.075274
    """
    return 0.409 * math.sin(2.0 * math.pi * doy / 365 - 1.39)