Question

The altitude of the earth at a place varies according to the seasons

Answer 1

because of the tilt of Earth's axis. During the summer the northern hemisphere is tilted toward the sun so it has summer and the southern hemisphere has winter, and during the winter it tilts the opposite way so the SH has summer and the NH has winter. This also makes the sun's altitude appear to change, as we move toward and away from it. The axis tilt is also responsible for the length of the days. 

Answer 2

because of the tilt of Earth's axis. During the summer the northern hemisphere is tilted toward the sun so it has summer and the southern hemisphere has winter, and during the winter it tilts the opposite way so the SH has summer and the NH has winter. This also makes the sun's altitude appear to change, as we move toward and away from it. The axis tilt is also responsible for the length of the days.