On a previous show we discussed how, every 250,000 years or so, the north and south poles switch places. Not that the places themselves move, rather, the entire magnetic field of the earth flips around, resulting in the pole we now call north being on the southern tip of the planet, and vice versa. Why does this happen? Learn more on this Moment of Science.
A sextant is a hand-held gadget that looks like the outline of a large piece of pizza. It is essential for navigation since it helps determine degrees of latitude, telling sailors how far to the north or south of the equator they are located.