On any spot on Earth, you can see only half the sky. Think of a sphere surrounding the Earth. Imagine the stars are drawn on the inside of this sphere (even though stars, of course, sit in space at varying distances—this is a thought experiment). An observer standing at the top of the sphere can't see the view down under—only half the sphere can be seen.

This celestial sphere surrounding Earth is split into northern and southern halves, called hemispheres. An observer at the North Pole can only see stars and constellations in the northern half of the celestial sphere. An observer living at mid-northern latitudes, between the North Pole and the equator, can see into about half the Southern Hemisphere.

Only on Earth's equator can the lucky stargazer see the highlights of both the northern and southern halves of the celestial sphere.

The southern sky is full of interesting objects, many of which are close to the south celestial pole and hidden from view to stargazers north of the equator. If you live in the north and are planning a trip south, things surprisingly familiar yet utterly strange await you.