What is  Sub-Solar Point?

A sub-solar point is a location on any planet which, at some time of a year, comes directly under the sun or the the sun is at the zenith.

The sun-light at the sub-solar point hits the surface, perpendicularly.

The sub-solar point can also be perceived as the the location closest to the sun.

Significance of Sub-Solar Point:

The sub-solar pint defines the locations of Tropic of Cancer and Tropic of Capricorn on Earth. The tropics are the two latitudes which mark the extreme North and South movement of sub-solar point throughout the year.

On Summer Solstice (21 June) the sub-solar point is on the tropic of cancer whereas on winter solstice (22 December) the sub-solar point is on the tropic of Capricorn. Moreover the sub-solar point always remains between the two tropics and reaches the equator, two times a year known as equinoxes.


The Tropics:

The tropics are two latitudes on the surface of earth that correspond to the maximum and minimum solar declination angle throughout the year.
The maximum declination angle occurs on June 21 and is equal to +23.4 degrees whereas the minimum declination angle occurs on December 21 and is equal to -23.4 degrees.