<P> The graph of apparent solar declination is therefore different in several ways from a sine wave . Calculating it accurately involves some complexity, as shown below . </P> <P> The declination of the Sun, δ, is the angle between the rays of the Sun and the plane of the Earth's equator . The Earth's axial tilt (called the obliquity of the ecliptic by astronomers) is the angle between the Earth's axis and a line perpendicular to the Earth's orbit . The Earth's axial tilt changes slowly over thousands of years but its current value of about ε = 23 ° 26' is nearly constant, so the change in solar declination during one year is nearly the same as during the next year . </P> <P> At the solstices, the angle between the rays of the Sun and the plane of the Earth's equator reaches its maximum value of 23 ° 26' . Therefore δ = + 23 ° 26' at the northern summer solstice and δ = − 23 ° 26' at the southern summer solstice . </P> <P> At the moment of each equinox, the center of the Sun appears to pass through the celestial equator, and δ is 0 ° . </P>

Based on the location of the sun which drawing is most accurate