Answer :
because the earth is tilted towards the poles,so in summers the north pole will have continuous daylight for 6 months and south pole will have night for 6 months.Then in winters it will be reversed i.e. north pole will have night for the other 6 months and south pole will have continuous day light for 6 months. this proves that the poles experience day for 6 months and other 6 months they experience night.
