Crossing another imaginary line…The Tropic of Cancer, also referred to as the Northern Tropic, is the most northerly circle of latitude on the Earth at which the Sun may appear directly overhead at its culmination. This event occurs once per year, at the time of the Northern solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent. As of 16 March 2015, it lies at 23°26′14.3″ north of the Equator. The Tropic of Capricorn and the Tropic of Cancer are two of the five major degree measures or major circles of latitude that mark maps of the Earth. The positions of these circles of latitude (other than the Equator) are dictated by the tilt of the Earth’s axis of rotation relative to the plane of its orbit. The Tropic of Cancer position is not fixed, but varies in a complicated manner over time. It drifts south almost half a second (0.47″) of latitude per year (it was at exactly 23° 27′ in year 1917).