The Sun can be seen at the zenith twice during the year. North circumpolar stars are seen. The Sun can be seen at the zenith only once during the year. North celestial pole seen at the zenith. All stars rise and set.
All northern stars are circumpolar.
Celestial poles are seen on the horizon. South celestial pole is seen at the zenith. All southern stars are circumpolar. The ecliptic can be seen directly overhead at local noon on June 21. The ecliptic can be seen directly overhead at local midnight on December 21.