The
subsolar point on a
planet is where its sun is perceived to be directly overhead (in
zenith); that is where the sun's
rays are hitting the planet exactly
perpendicular to its surface. It can also mean the point closest to the sun on an object in space, even though the sun might not be visible. For planets with an orientation and rotation similar to the
Earth's, the subsolar point will move westward, circling the
globe once a day, but it will also move north and south between the
tropics over the course of a year. The
December solstice occurs when the subsolar point is on the
Tropic of Capricorn and the
June solstice is at the instant when the subsolar point is on the
Tropic of Cancer. The
March and
September equinoxes occur when the subsolar point is on the
equator. The subsolar point is frequently used in
celestial navigation and the coordinates of the subsolar point at various times throughout the year (often every hour) can be found in a
nautical almanac. When the point passes through
Hawaii, it is known as
Lahaina Noon.