The Earth showing the Tropic of Capricorn at 23.5 degrees south of the equator.

On the northern winter solstice/southern summer solstice (around the 22nd December each year), the Sun reaches its most southerly declination of -23.5 degrees. At this time, the Sun is directly overhead for an observer on the Tropic of Capricorn. 3,000 years ago, this occurred when Sun was in the zodiac constellation Capricorn, and even though this is not longer the case (due to the precession of the equinoxes), the name remains.