The Tropic of Cancer is the line of latitude at about 23.5 degrees north that crosses Mexico, Egypt, and India.
It marks the northernmost latitude at which the Sun can appear directly overhead at noon. This occurs around the June solstice, when the Northern Hemisphere is tilted toward the Sun.
The line is not fixed perfectly at 23.5 degrees because Earth’s axial tilt changes slowly over long periods. Its modern position is roughly 23 degrees 26 minutes north, and it gradually shifts because of variations in Earth’s obliquity.
The name comes from the constellation Cancer, where the Sun appeared during the June solstice in ancient times. Because of precession, the Sun no longer appears in Cancer at that solstice, but the geographic name remains.