What latitude line marks the northernmost point where the sun can be directly overhead?

The Tropic of Cancer is the northernmost latitude where the Sun can appear directly overhead.

This happens because Earth’s axis is tilted about 23.4 degrees relative to its orbit. At the June solstice, the Northern Hemisphere tilts toward the Sun, placing the Sun’s subsolar point—the location where its rays strike most directly—near the Tropic of Cancer, at about 23.4° north latitude.

The Tropic of Capricorn is the corresponding southern limit, while the Equator lies midway between the two tropics. The Arctic Circle is not the northernmost overhead-Sun limit: it marks the approximate boundary of 24-hour daylight or darkness at the solstices.

The line’s name comes from the constellation Cancer. Because of the slow precession of Earth’s axis, the June-solstice Sun is now seen against Taurus rather than Cancer, although the geographic name remains unchanged.