The tilt of the Earth’s axis of rotation and the Earth’s rotation around the sun cause the declination angle, represented as, to change periodically. The declination would always be 0° if the Earth’s axis of rotation weren’t slanted. However, because of the Earth’s tilt, which is 23.45°, there is some variability in the declination angle.
The declination angle is just 0° at the spring and fall equinoxes. The angle formed between the equator and a line drawn from the centre of the Earth to the centre of the sun is known as the sun’s declination.
What is the Formula of Deviation Angle?
The formula: can be used to determine the declination angle.
δ=−23.45°×—cos(360/365×—(d+10))
where d is the day of the year, and d = 1 on January 1st.
The declination is zero on March 22 and September 22 at the equinoxes, positive in the summer and negative in the winter in the northern hemisphere. The declination is at its highest point on June 22 (summer solstice in the northern hemisphere) and its lowest point on December 21–22, when it is 23.45°. (winter solstice in the northern hemisphere).
The fact that the winter solstice falls before the year’s commencement accounts for the +10 in the calculation above. The equation also makes the assumption that the sun’s orbit is a perfect circle. The conversion of the day number to an orbital location uses the factor 360/365.
Also Read: What is a Conduction Band?
What is the Declination Angle Variance?
A sine wave with an amplitude of 23.44 will look similar to a line graph representing the Sun’s declination over the course of a year. Since the Earth’s orbit is elliptical, its motion around the sun is faster in early January near the perihelion than in early July near the aphelion.
Due to this, solar declination variation occurs far more quickly in January than in July. Also, the minima and maxima become slightly asymmetrical, and the change rate is not really equal before and after, because perihelion and aphelion do not occur on the same dates as the solstices.
