Archaeoastronomy - The Zenith Passage of the Sun

The tropics are the regions of the Earth that lie between the latitude lines of the Tropic of Cancer and the Tropic of Capricorn. In this zone of the Earth, we have the opportunity to see the zenith passage of the sun, that is, we can see the sun passing at noon directly overhead. 
The zenith passage happens on two days in the year. These days depend upon the latitude of the place of observation. Let us note that, at the Tropic of Cancer, the zenith passage happens on the day of the June solstice and at the Tropic of Capricorn on that of the December solstice; at the equator, the zenithal sun is observed on the two equinoxes.
When the sun passes overhead, the shadows disappear and the days when this happens assume a sacred significance for the people that live and lived within the tropics. Being the zenith passage so important, it is not surprising that we can find it evidenced by the local architectures too. We have, for instance, that some monuments possess a "zenith tube" at their apex, such as  at Angkor Wat, Cambodia. It is a vertical sighting tube inserted in the vault of the structure, which produces in a dark chamber a perfectly perpendicular beam of light when the sun is at the local zenith.
As we will see, alignments of monuments are also possible: we observed them in Sanchi, India,  at the Lion Rock in Sri Lanka, in Angkor Wat and at the Sewu, Prambanan and Borobudur Temples in Java. We can observe alignments at the Mesoamerican Sites of Tula and Chichen Itza. Here we also show alignments to the sunrise of the zenithal sun at the Shwedagon Pagoda and in the plan of Brasilia.