The Earth showing the Tropic of Cancer at 23.5 degrees north of the equator.

The Tropic of Cancer is a parallel of latitude on the Earth, 23.5 degrees north of the equator.

On the northern summer solstice/southern winter solstice (around the 21st June each year), the Sun reaches its most northerly declination of +23.5 degrees. At this time, the Sun is directly overhead for an observer on the Tropic of Cancer. 3,000 years ago, this occured when Sun was in the zodiac constellation Cancer, and even though this is not longer the case (due to the precession of the equinoxes), the name remains.

The declination of the Sun and the latitude of the a Tropic of Cancer are equal to the obliquity of the ecliptic, the angle that the ecliptic makes with the celestial equator.