Sun's declination is the angular distance from north to south of the celestial equator. The delineations of the sun change from 23.5 degrees North to 23.5 degrees South and back again during a year.
As the seasons change the time the sun stays at the earth atmosphere also changes from day to night like at the time of Solstice in winter and summer. The dates of these solstices change from time to time according to the rotation of the earth.
As te places on the earth latitude have delineated over the period that has caused the coordinates to change continuously. There is an increase and then decrease of this definition from east to west in some latitudes and west to est in others related to the north and south pole alignments of the earth.
