Why are the days longer in summer than in winter?

The axis of rotation of the Earth is tilted, and this can be seen clearly in a globe. 

Around  June 21,the axis points clearly towards the sun (see the figures).As a result a large part of the Northern hemisphere is illuminated by a strong sun and day time remains long till the rotation of the Earth cause this area to move away from the direct glory of sun light. The place, thus, has long hours of sun light and the days are long.In fact, the sun shines over the North pole continuously for several weeks without setting even once. This period is knowns as the 'polar day '.

During Christmas 🎄, the axis of the Earth points away from the sun. During these days, the Northern hemisphere remains dark for a longer period of time and a 'polar night 'sets in at the North pole.On the other hand, the southern hemisphere enjoys long hours of pun.