Subsolar point
What is the subsolar point?
It is the one place on Earth where the Sun is straight overhead right now — where a flagpole casts no shadow. It is the yellow dot on the day/night map, and it is where the Sun-centre to Earth-centre line hits the surface.
A lap a day, a bounce a year
Earth turns. The overhead point therefore races west, once around the planet each day, at the speed of the ground under it — about 1,670 km/h at the equator.
It also drifts north and south with the seasons, because of the tilt. In June it reaches the Tropic of Cancer. In December it reaches the Tropic of Capricorn. It never leaves that band.
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How this page finds it
The map does not look up a table of “where the Sun is.” It solves a low-precision solar series (the same one used for sunrise on this site): the Sun’s apparent ecliptic longitude, the obliquity, then declination and right ascension. Declination is the latitude of the subsolar point. Greenwich sidereal time turns right ascension into longitude.
That is why the yellow dot and the side-view hit are the same number. One series, two pictures.