Why the northern and southern tips of the hemisphere is both light and dark six months of the year?

Question

Why the northern and southern tips of the hemisphere is both light and dark six months of the year?

Answer 1

The Earth's axis of rotation isn't straight up and down with respect to the orbit.  It's tilted. As the Earth goes around the Sun, it keeps pointing in the same direction - the North pole points near the star Polaris all the time.

In the northern hemisphere summer, the north pole is tipped towards the Sun.  If you're far enough North, like at the pole, the Sun never sets.  You can try this with a flashlight and a globe.  And at this time, it's winter in the South, and the south pole is always in darkness because that half of the Earth is tipped away from the Sun.

Now as the Earth goes around to the other side of the Sun, it's axis stays the same, but now the North is pointing away from the Sun and the South is pointing towards the Sun.  So the North gets no Sun at all, and the South gets it all the time.

In Spring and Fall, both hemispheres get day and night as usual.  So it's not six months of light and dark, but more like three.

Answer 2

Because the Earth is titled on its axis with respect to the Sun. So for half the orbit, one pole or the other is pointing away from the sun.

Answer 3

Because of the tilt of the Earth's axis.

Answer 4

Though you did not mention, it is presumed that your hemisphere are Earth's northern & southern hemispheres.

Tilted at 23.45d, they bend towards or away (after 6 months) from Sun.

As the tip looks at the Sun while revolving, a cap of 23.45d  is always exposed to Sun. This translates to, that the Sun is always shining there or it is daylight in that cap. The tip being at 90d, the cap extends down from it to 90 - 23.45 = 66.55 degrees that is called either Arctic circle or Antarctic circle that is the limit of the midnight Sun or 6 month winter area.

If the tip points away, the other (southern) tip points now to the Sun with the same consequences there.