In the nothern hemisphere, the north star (and circumpolar stars) are visible any night of the year. The reason the southern constellations vary with the seasons is due to earth's orbit of the sun. In winter the earth is on the opposite side of the sun as it is in the summer, thus the winter night sky is very different from the summer night sky. The winter day sky resembles more closely the summer night sky, if the sun weren't there to block instreaming starlight.