Tropic of Cancer Marks Tower

Recently, my wife and I went on a tour to Santou, a city in the Guangdong province of China. We came across a place where the Tropic of Cancer Marks Tower was built. As the Marks Tower was hidden from the highway, we missed it on our way to Meizhou ( the ancestral town of the Hakka people). On the return trip, we finally arrived at the site where a tower of a globe was built.

Tropic of Cancer Marks Tower

There is a cylindrical channel in the middle of the Globe which pierced the Globe from top to bottom. There is a small circle marked on the floor where the hole falls vertically below it. If one stands on this circle and looks up on 23rd of March at 12 noon of the year, the sun will appear directly above his head and no shadow will be cast on the floor.

A cylindrical channel that runs from top to bottom of the Globe

The entrance to the Tower

Signage at the site

The Tropic of Cancer, also referred to as the Northern tropic, is the circle of latitude on the Earth that marks the most northerly position at which the Sun may appear directly overhead at its zenith. This event occurs once per year, at the time of the June solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent. As of 2013^[update], it lies at 23° 26′ 15.143″ (23° 26′ 16″) north of the Equator.

The imaginary line is called the Tropic of Cancer because when the Sun reaches the zenith at this latitude, it is entering the tropical sign of Cancer (summer solstice in the northern hemisphere). When it was named, the Sun was also in the direction of the constellation Cancer (Latin for crab). However, this is no longer true due to the precession of the equinoxes. According to NASA observations, the Sun is now in Gemini at the June solstice. 

 According to sidereal astrology, which divides the zodiac into 12 equal parts, the Sun is in Gemini at that time. However, according to tropical astrology, which divides the ecliptic in twelve 30° sectors, starting with the vernal equinox, the Sun is always entering Cancer at this time, as the Earth's axial tilt is most inclined towards the Sun. The word "tropic" itself comes from the Greek tropos, meaning turn, referring to the fact that the sun appears to "turn back" at the solstices. (Text from Wikipedia)