Since Zenith angle= latitude of interest- solar declination
Latitude of interest=40 degree N
Solar declination=-231/2 degree S
Therefore zenith angle=40- 23/12
=16.5
Since the zenith angle is equal to the latitude separating the
person at 40 degree latitude and the place recieving direct sun
light. Therefore the value of this angle is 16.5 degree.
Now, declination angle= sin-1 sin(23.5 degree) sin
360/365(d-81)
where d= no of days=??
-231/2=sin-1sin(23.5 degree)sin 360/365( d-81)
-23/12=sin-1(0.398)sin0.98(d-81)
-231/2=sin-1(0.398)(0.017)(d-81)
-231/2=sin-1(0.00676)(d-81)
-231/2=0.387(d-81)
(231/2)/(0.387)=d-81
60.7=d-81
d=60.7+81
=141.7
=142
Therefore 142 will be either 22th or 23 th of May starting d=1
as January 1st.
3.Solar elevation angle= 90-zenith angle
=90-19.5
=73.5 degree
