How does your latitude determine which constellations are circumpolar when viewed from your location?

Answer 1

Assume Earth is a perfectly smooth sphere with no atmospheric haze to obscure vision. If you stand on the equator of this polished Earth you will see the pole star sitting on the northern horizon and the southern celestial pole will sit on the southern horizon. There will be no circumpolar stars at that location.

If you go ten degrees north, the pole star will be ten degrees above the horizon. Since the stars appear to rotate around the pole star, and star less than ten degrees from that star will never set, because when it reaches the lowest point in the sky it will lie between the pole star and the horizon. In effect there is a ten degree circle around the pole star, any star or constellation within which will be circumpolar. If you go to a latitiude of twenty degrees the circle will expland to twenty degrees. If you go to the pole, 90 degrees north, the circle expands to 90 degrees, and that circle contains the entire northern sky, so everything is circumpolar.