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 equinoxes 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.
- Ian Ridpath, ed. (1997). "subsolar point". A Dictionary of Astronomy. Oxford; New York: Oxford University Press. ISBN 0-19-211596-0. "The point on the Earth, or other body, at which the Sun is directly overhead at a particular time."
- Nancy Alima Ali (May 11, 2010). "Noon sun not directly overhead everywhere". Honolulu Star-Bulletin. Retrieved November 12, 2010.
- Day and Night World Map (shows location of subsolar point for any user-specified time)
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