Ruth Stack of Palmerston North asks :-
Why does the direction of the sun rise vary during the year. For the Manawatu, what are the extremes during the year?
Alan Gilmore, an astronomer at the University of Canterbury's Mt John Observatory, responded.
Through the year the noonday altitude of the sun changes. This gives the seasons. The higher the sun in the sky, the more intense the light and heat on the ground and the warmer the weather. A low sun spreads the light and heat over a larger area, so temperatures are cooler.
The change in altitude of the sun also causes its rise and set azimuth to vary over the year. At the summer solstice, around December 21st, the sun rises 122 degrees from true north, roughly in the southeast, seen from the Manawatu. At equinox, March 21 or 22, the sunrise is due east. At the winter solstice, June 21, the sun rises 59 degrees from due north, roughly northeast.
The sunset angles are the same, measured from due north toward the west. The summer solstice sun sets in the southwest; the equinoctial sun in the west, and winter solstice sun in the northwest. These different tracks of the sun make our days longer or shorter. The summer solstice sun takes nearly 15 hours to cross the sky. The winter solstice sun takes just 9 hours. So not only is winter sunlight weaker but we get it for a shorter time.
The changes in rise/set azimuths and noonday altitude are caused by the tilt of the earth's axis to its orbital plane. If the earth's axis was vertical to the orbit plane then we wouldn't have seasons: the sun would always rise in the east and set in the west and be in the sky for 12 hours. In fact the axis is tilted 23 degrees from the vertical. So in December-January the southern hemisphere is tilted toward the sun giving us summer and northerners winter. On the other side of Earth's orbit, in June-July, the northern hemisphere is tilted toward the sun giving them summer and us winter.